Journal of Vision Articles via MedWorm.com

Corrections to: Optimal stimulus encoders for natural tasks

Journal of Vision Articles — Fri, 26 Feb 2010 00:00:00 +0100

(Source: Journal of Vision Articles)

Corrections to: Top-down flow of visual spatial attention signals from parietal to occipital cortex

Journal of Vision Articles — Fri, 26 Feb 2010 00:00:00 +0100

(Source: Journal of Vision Articles)

Holistic perception of individual faces in the right middle fusiform gyrus as evidenced by the composite face illusion

Journal of Vision Articles — Fri, 26 Feb 2010 00:00:00 +0100

The perception of a facial feature (e.g., the eyes) is influenced by the position and identity of other features (e.g., the mouth) supporting an integrated, or holistic, representation of individual faces in the human brain. Here we used an event-related adaptation paradigm in functional magnetic resonance imaging (fMRI) to clarify the regions representing faces holistically across the whole brain. In each trial, observers performed the same/different task on top halves (aligned or misaligned) of two faces presented sequentially. For each face pair, the identity of top and bottom parts could be both identical, both different, or different only for the bottom half. The latter manipulation resulted in a composite face illusion, i.e., the erroneous perception of identical top parts as being d...

Distortions in recall from visual memory: Two classes of attractors at work

Journal of Vision Articles — Wed, 24 Feb 2010 00:00:00 +0100

In a trio of experiments, a matching procedure generated direct, analogue measures of short-term memory for the spatial frequency of Gabor stimuli. Experiment 1 showed that when just a single Gabor was presented for study, a retention interval of just a few seconds was enough to increase the variability of matches, suggesting that noise in memory substantially exceeds that in vision. Experiment 2 revealed that when a pair of Gabors was presented on each trial, the remembered appearance of one of the Gabors was influenced by: (1) the relationship between its spatial frequency and the spatial frequency of the accompanying, task-irrelevant non-target stimulus; and (2) the average spatial frequency of Gabors seen on previous trials. These two influences, which work on very different time scale...

(In) Sensitivity to spatial distortion in natural scenes

Journal of Vision Articles — Wed, 24 Feb 2010 00:00:00 +0100

The perception of object structure in the natural environment is remarkably stable under large variation in image size and projection, especially given our insensitivity to spatial position outside the fovea. Sensitivity to periodic spatial distortions that were introduced into one quadrant of gray-scale natural images was measured in a 4AFC task. Observers were able to detect the presence of distortions in unfamiliar images even though they did not significantly affect the amplitude spectrum. Sensitivity depended on the spatial period of the distortion and on the image structure at the location of the distortion. The results suggest that the detection of distortion involves decisions made in the late stages of image perception and is based on an expectation of the typical structure of nat...

Amplitudes and directions of individual saccades can be adjusted by corollary discharge

Journal of Vision Articles — Tue, 23 Feb 2010 00:00:00 +0100

There is strong evidence that the brain can use an internally generated copy of motor commands, a corollary discharge, to guide rapid sequential saccades. Much of this evidence comes from the double-step paradigm: after two briefly flashed visual targets have disappeared, the subject makes two sequential saccades to the targets. Recent studies on the monkey revealed that amplitude variations of the first saccade led to compensation by the second saccade, mediated by a corollary discharge. Here, we investigated whether such saccade-by-saccade compensation occurs in humans, and we made three new observations. First, we replicated previous findings from the monkey: following first saccade amplitude variations, the direction of the second saccade compensated for the error. Second, the change i...

Comparing reading speed for horizontal and vertical English text

Journal of Vision Articles — Tue, 23 Feb 2010 00:00:00 +0100

There are three formats for arranging English text for vertical reading—upright letters arranged vertically (marquee), and horizontal text rotated 90° clockwise or counterclockwise. Previous research has shown that reading is slower for all three vertical formats than for horizontal text, with marquee being slowest (M. D. Byrne, 2002). It has been proposed that the size of the visual span—the number of letters recognized with high accuracy without moving the eyes—is a visual factor limiting reading speed. We predicted that reduced visual-span size would be correlated with the slower reading for the three vertical formats. We tested this prediction with uppercase and lowercase letters. Reading performance was measured using two presentation methods: RSVP (Rapid Serial Visual Presenta...

Are discrimination thresholds a valid measure of variance for judgments of slant from texture?

Journal of Vision Articles — Tue, 23 Feb 2010 00:00:00 +0100

There have been many experiments reported in the literature that have employed discrimination procedures to estimate the variance of observers' slant judgments from texture and binocular disparity, both individually and in combination. The research described in the present article identifies two serious methodological flaws in these studies. Although discrimination thresholds can be influenced by the variance of observers' slant estimates, they can also be affected by systematic biases in observers' judgments, and the presence of 2D cues that are irrelevant to the perception of slant. A series of five experiments is reported to show that: (1) the slants of surfaces specified by texture gradients can be systematically underestimated; (2) surfaces specified by texture gradients appear signif...

Perceptual preferences in depth stratification of transparent layers: Photometric and non-photometric factors

Journal of Vision Articles — Tue, 23 Feb 2010 00:00:00 +0100

In three experiments, using a two-alternative forced-choice task, we obtained depth judgments of displays containing transparent regions. The regions varied in lightness, size, and animation. Observers nearly always strongly preferred one certain depth ordering among the regions, even though their lightness conditions were expected to give rise to ambiguity among possible orderings. This expectation was based on the contrast polarity model, which expects ambiguity in the absence of contrast polarity reversal. The expectation was founded also on a stronger condition based on the transmittance anchoring principle, which gives preference to the largest lightness contrast between regions. In the absence of contrast polarity reversal and in conditions of balanced regional contrast, preferences ...

Beauty and the beholder: Highly individual taste for abstract, but not real-world images

Journal of Vision Articles — Mon, 22 Feb 2010 00:00:00 +0100

How individual are visual preferences? For real-world scenes, there is high agreement in observer's preference ratings. This could be driven by visual attributes of the images but also by non-visual associations, since those are common to most individuals. To investigate this, we developed a set of novel abstract, visually diverse images. At the individual observer level both abstract and real-world images yielded robust and consistent visual preferences, and yet abstract images yielded much lower across observer agreement in preferences than did real-world images. This suggests that visual preferences are typically driven by the semantic content of stimuli, and that shared semantic interpretations then lead to shared preferences. Further experiments showed that highly individual preferenc...

Transfer of object learning across distinct visual learning paradigms

Journal of Vision Articles — Mon, 22 Feb 2010 00:00:00 +0100

We present the first study designed to investigate whether visual object learning is specific to the type of stimulus degradation used. Sixteen participants were trained to recognize common objects. Half of them was trained in a backward masking paradigm, the other half in a simultaneous noise addition paradigm. After five days, performance was measured in four tests: (1) the trained paradigm with the trained objects, (2) the trained paradigm with new objects, (3) the untrained paradigm with the trained objects and (4) the untrained paradigm with new objects. Training effects were specific for the trained objects. In addition, an object-specific transfer to the untrained paradigm was found. The group trained in the simultaneous noise addition paradigm showed a complete transfer of performa...

Adaptation-induced blindness to sluggish stimuli

Journal of Vision Articles — Wed, 17 Feb 2010 00:00:00 +0100

It is well known that prolonged observation of a dynamic visual pattern raises the contrast threshold for a subsequently presented static pattern. We found that if the post-adaptation test was presented gradually, so that its onset transient was weak, the test pattern was undetectable even at high contrast. Although the smooth-onset patterns were invisible, they caused apparent shifts in the orientation and contrast of neighboring stimuli, indicating the implicit processing of the target features. However, this strong aftereffect was not obtained if the target grating drifted rapidly or was onset abruptly. These results suggest that when human observers become less sensitive to transients in stimuli due to dynamic adaptation, they cannot consciously perceive sluggish stimuli containing wea...

Limits of peripheral direction discrimination of point-light walkers

Journal of Vision Articles — Wed, 17 Feb 2010 00:00:00 +0100

Many previous studies have used noise tolerance to quantify sensitivity to point-light walkers heading ±90° from straight-ahead. Here we measured the smallest deviations from straight-ahead that observers could detect (azimuth thresholds) in the absence of noise. Thresholds were measured at a range of stimulus sizes and eccentricities for (1) upright and (2) inverted walkers, (3) intact walkers, those without feet and those with only feet, and (4) in the presence and absence of a second, attention-absorbing task. At large stimulus sizes azimuth thresholds were very small (between 1 and 2°) except in the case of inverted walkers. Size scaling generally compensated for eccentricity dependent sensitivity loss, however in the case of inverted walkers the data were quite noisy. At large size...

Capacity limits during perceptual encoding

Journal of Vision Articles — Tue, 16 Feb 2010 00:00:00 +0100

When a unique stimulus is embedded in an otherwise homogenous display, it is thought to “pop-out” due to its relative increase in salience. We investigated whether the visual system has the ability to equally prioritize multiple salient pop-out items competing for awareness or whether this early stage of visual processing is constrained by capacity limits. We used signal detection (d′) methods to determine if sensitivity to a salient pop-out item decreases as function of the number of total salient items present in the visual display. Participants engaged in a signal detection task where they had to report the presence or absence of a simple display change that involved either a pop-out or a non-salient distractor stimulus. Results across four experiments consistently showed that sen...

Quantifying and modeling the strength of motion illusions perceived in static patterns

Journal of Vision Articles — Tue, 16 Feb 2010 00:00:00 +0100

The origin of motion illusions in simple black and white patterns such those as used by Op artists has been at the center of a lively scientific debate, relating motion processing mechanisms to involuntary eye movements that generate characteristic motion patterns. To overcome the limitations of using subjective ratings as a measure of illusory effects, we developed a new method to quantify the strength of the illusion for synthetic ‘riloids’ that were inspired by Bridget Riley's ‘Fall’. In a 2AFC paradigm, test stimuli were compared to a reference set of patterns that elicit illusory motion of variable strength. We found that pattern parameters influencing the distribution of local orientation in the riloids (the amplitude and the spatial period of the line undulation) systematica...

Human scotopic sensitivity is regulated postreceptorally by changing the speed of the scotopic response

Journal of Vision Articles — Tue, 16 Feb 2010 00:00:00 +0100

Sensitivity regulation enables the visual system to function effectively from the absorption of a few photons at the lowest visual threshold to the absorption of enough photons to bleach nearly all the light-sensitive photopigment in the eye. Here, we investigate sensitivity regulation in the rod (or scotopic) range from −3.8 to −0.8 log10 scotopic trolands. Over most of this range, the rate of photon absorption per rod is too low for sensitivity regulation to be practicable within the rod photoreceptor itself, so that regulation must occur postreceptorally. We measured adaptation-dependent changes in visual sensitivity and visual delay, which together provide a much more complete characterization of the effects of light adaptation than the usual method of measuring sensitivity changes...

Rod and cone contrast gains derived from reaction time distribution modeling

Journal of Vision Articles — Fri, 12 Feb 2010 00:00:00 +0100

Contrast gain reflects the rapidity of response amplitude increase with increase in stimulus contrast. In physiology, contrast gain can be measured directly as the initial slope of cell contrast response function. In psychophysics, contrast gain estimation is not straightforward. Further, rod and cone contrast gains have not been measured psychophysically at mesopic light levels where both rods and cones are active, due to the difficulty in producing stimuli that excite rods and cones separately at the same adaptation level. Here, we estimated rod and contrast gains by fitting reaction time distributions measured at a light level in which rods alone (scotopic), rods and cones (mesopic), or cones alone (photopic) mediate vision. The reaction time distributions were modeled by two different ...

Vision senses number directly

Journal of Vision Articles — Fri, 12 Feb 2010 00:00:00 +0100

We have recently suggested that numerosity is a primary sensory attribute, and shown that it is strongly susceptible to adaptation. Here we use the Method of Single Stimuli to show that observers can extract a running average of numerosity of a succession of stimuli to use as a standard of comparison for subsequent stimuli. On separate sessions observers judged whether the perceived numerosity or density of a particular trial was greater or less than the average of previous stimuli. Thresholds were as precise for this task as for explicit comparisons of test with standard stimuli. Importantly, we found no evidence that numerosity judgments are mediated by density. Under all conditions, judgements of numerosity were as precise as those of density. Thresholds in intermingled conditions, wher...

Visual motion detection sensitivity is enhanced by orthogonal induced motion

Journal of Vision Articles — Fri, 12 Feb 2010 00:00:00 +0100

We presented the central Gabor patch, which was barely moving to the left or right, together with a surrounding grating moving vertically. Subjects were asked to judge whether the central stimulus was moving left or right, and thus the illusory vertical motion itself was task-irrelevant. We found that the performance on the horizontal test was enhanced when it was combined with the induced vertical motion, which resulted in the central motion appearing slightly oblique rather than purely horizontal. Our results indicate that the later stage, in which motion integration and center–surround interaction appears, is critical for determining the perceptual limit of motion detection. (Source: Journal of Vision Articles)

Real and predicted influence of image manipulations on eye movements during scene recognition

Journal of Vision Articles — Thu, 11 Feb 2010 00:00:00 +0100

In this paper, we investigate how controlled changes to image properties and orientation affect eye movements for repeated viewings of images of natural scenes. We make changes to images by manipulating low-level image content (such as luminance or chromaticity) and/or inverting the image. We measure the effects of these manipulations on human scanpaths (the spatial and chronological path of fixations), additionally comparing these effects to those predicted by a widely used saliency model (L. Itti & C. Koch, 2000). Firstly we find that repeated viewing of a natural image does not significantly modify the previously known repeatability (S. A. Brandt & L. W. Stark, 1997; D. Noton & L. Stark, 1971) of scanpaths. Secondly we find that manipulating image features does not necessarily change th...

Temporal auditory capture does not affect the time course of saccadic mislocalization of visual stimuli

Journal of Vision Articles — Thu, 11 Feb 2010 00:00:00 +0100

Irrelevant sounds can “capture” visual stimuli to change their apparent timing, a phenomenon sometimes termed “temporal ventriloquism”. Here we ask whether this auditory capture can alter the time course of spatial mislocalization of visual stimuli during saccades. We first show that during saccades, sounds affect the apparent timing of visual flashes, even more strongly than during fixation. However, this capture does not affect the dynamics of perisaccadic visual distortions. Sounds presented 50 ms before or after a visual bar (that change perceived timing of the bars by more than 40 ms) had no measurable effect on the time courses of spatial mislocalization of the bars, in four subjects. Control studies showed that with barely visible, low-contrast stimuli, leading, but not trai...

Biological motion drives perception and action

Journal of Vision Articles — Thu, 11 Feb 2010 00:00:00 +0100

In this study, we investigate whether this biological motion perception network could influence the smooth pursuit response evoked by a point-light walker. We found that smooth eye velocity during pursuit initiation was larger in response to the point-light walker than in response to one of its scrambled versions, to an inverted walker or to a single dot stimulus. In addition, we assessed the proximity to the point-light walker (i.e. the amount of information about the direction contained in the scrambled stimulus and extracted from local motion cue of biological motion) of each of our scrambled stimuli in a motion direction discrimination task with manual responses and found that the smooth pursuit response evoked by those stimuli moving across the screen was modulated by their proximity ...

Neurophysiological evidence for the influence of past experience on figure–ground perception

Journal of Vision Articles — Wed, 10 Feb 2010 00:00:00 +0100

A fundamental aspect of perceptual organization entails segregating visual input into shaped figures presented against shapeless backgrounds; an outcome termed “figure–ground perception” or “shape assignment.” The present study examined how early in processing past experience exerts an influence on shape assignment. Event-related potential (ERP) measures of brain activity were recorded while observers viewed silhouettes of novel objects that differed in whether or not a familiar shape was suggested on the outside—the groundside—of their bounding edges (experimental versus control silhouettes, respectively). Observers perceived both types of silhouettes as novel shapes and were unaware of the familiar shape suggested on the groundside of experimental silhouettes. Nevertheless,...

Combining top-down processes to guide eye movements during real-world scene search

Journal of Vision Articles — Wed, 10 Feb 2010 00:00:00 +0100

Eye movements can be guided by various types of information in real-world scenes. Here we investigated how the visual system combines multiple types of top-down information to facilitate search. We manipulated independently the specificity of the search target template and the usefulness of contextual constraint in an object search task. An eye tracker was used to segment search time into three behaviorally defined epochs so that influences on specific search processes could be identified. The results support previous studies indicating that the availability of either a specific target template or scene context facilitates search. The results also show that target template and contextual constraints combine additively in facilitating search. The results extend recent eye guidance models by...

Positional priming of pop-out: A relational-encoding account

Journal of Vision Articles — Wed, 10 Feb 2010 00:00:00 +0100

Three experiments examined whether positional priming of pop-out is modulated by target salience. In Experiment 1, the singleton target appeared among variable numbers of distractors (2, 3, 5, 7; blocked presentation). While facilitation of target locations was not influenced by distractor number, inhibition of distractor locations was evident only with two distractors in the display. In Experiment 2, 3- and 6-item displays, with 2 and 5 distractors, respectively, were intermixed rather than blocked. It was found that, when the majority (but not the minority) of trials contained 3-item displays, there was carryover of distractor location inhibition from 3- to 6-item displays (but not vice versa). In Experiment 3 (1 target, 2 distractors), inhibitory priming of distractor locations could ev...

Visual learning with reliable and unreliable features

Journal of Vision Articles — Thu, 04 Feb 2010 00:00:00 +0100

Existing studies of sensory integration demonstrate how the reliabilities of perceptual cues or features influence perceptual decisions. However, these studies tell us little about the influence of feature reliability on visual learning. In this article, we study the implications of feature reliability for perceptual learning in the context of binary classification tasks. We find that finite sets of training data (i.e., the stimuli and corresponding class labels used on training trials) contain different information about a learner's parameters associated with reliable versus unreliable features. In particular, the statistical information provided by a finite number of training trials strongly constrains the set of possible parameter values associated with unreliable features, but only wea...

The effect of normal aging on closed contour shape discrimination

Journal of Vision Articles — Thu, 04 Feb 2010 00:00:00 +0100

Our experiments explore whether contour processing of closed shapes is altered by healthy aging. Contour processing was measured using a closed contour (circle or ellipse) constructed of Gabor elements. The contour was presented either on a blank background or embedded in noise (identical Gabor elements of random orientation). Twenty-one older (age range: 61–80 years) and 21 younger (age range: 22–38 years) adults participated in three experiments: 1) the number of Gabors comprising the contour was fixed (10, 12 or 15) and the threshold aspect ratio required to discriminate the shape (circle versus ellipse) was measured; 2) orientation jitter was added to the Gabor elements comprising the contour and shape aspect ratio discrimination thresholds were measured; and 3) the aspect ratio wa...

Inverting faces elicits sensitivity to race on the N170 component: A cross-cultural study

Journal of Vision Articles — Fri, 29 Jan 2010 00:00:00 +0100

Human beings are natural experts at processing faces, with some notable exceptions. Same-race faces are better recognized than other-race faces: the so-called other-race effect (ORE). Inverting faces impairs recognition more than for any other inverted visual object: the so-called face inversion effect (FIE). Interestingly, the FIE is stronger for same- compared to other-race faces. At the electrophysiological level, inverted faces elicit consistently delayed and often larger N170 compared to upright faces. However, whether the N170 component is sensitive to race is still a matter of ongoing debate. Here we investigated the N170 sensitivity to race in the framework of the FIE. We recorded EEG from Western Caucasian and East Asian observers while presented with Western Caucasian, East Asian...

Lengthy suppression from similar stimuli during rapid serial visual presentation

Journal of Vision Articles — Fri, 29 Jan 2010 00:00:00 +0100

The stimulus at any point in the visual field is rarely static during normal viewing: observer and object movement conspire to produce a continually changing series of stimuli. Our aim was to study both the short- and long-term interactions between responses to a series of stimuli presented at a single visual location. We used rapid serial visual presentation (RSVP) in which the stimuli were randomly oriented gratings delivered at the rate of 30 per second. Human subjects pressed a key whenever they saw a target orientation, for example horizontal. The results were analyzed by finding two orientations before each key-press. The first preceded the key-press by the reaction time, and the second preceded the first by an interval of variable duration. There were two main findings. First, the s...

Initiation of the optokinetic response (OKR) in mice

Journal of Vision Articles — Fri, 29 Jan 2010 00:00:00 +0100

To study the initial part of the mouse optokinetic response, OKR (~500 ms from the onset of visual stimulus motion), we recorded the ocular response to a vertical sinusoidal grating moving at a constant velocity. We found that the magnitude of the response monotonically increased as the stimulus contrast increased. The response showed a narrow band-pass property for the spatiotemporal frequency, with the largest sustained response observed at 0.125 cycle/deg and 1.5 Hz. We also found that temporal frequencies higher than 1.5 Hz elicited transient increase in the eye velocity, but weak or no sustained eye movements. Thus the initial OKR in mice is characterized by the spatiotemporal frequency of the visual stimuli. Our results suggest that the initial OKR contains two components: a transien...

Effects of task and coordinate frame of attention in area 7a of the primate posterior parietal cortex

Journal of Vision Articles — Wed, 27 Jan 2010 00:00:00 +0100

The activity of neurons in the primate posterior parietal cortex reflects the location of visual stimuli relative to the eye, body, and world, and is modulated by selective attention and task rules. It is not known however how these effects interact with each other. To address this question, we recorded neuronal activity from area 7a of monkeys trained to perform two variants of a delayed match-to-sample task. The monkeys attended a spatial location defined in either spatiotopic (world-centered) or retinotopic (eye-centered) coordinates. We found neuronal responses to be remarkably plastic depending on the task. In contrast to previous studies using the simple version of the delayed match-to-sample task, we discovered that after training in a task where the locus of attention shifted durin...

The Müller-Lyer Illusion: Investigation of a Center of Gravity Effect on the Amplitudes of Saccades

Journal of Vision Articles — Thu, 21 Jan 2010 00:00:00 +0100

Previous research has compared the effects of visual illusions on perception with their effects on action to investigate if the action system and the perceptual system use different or common codes. Appropriate conclusions based on this comparison rely on effects that reflect the internal parameter estimates of the action and of the perceptual system. We investigated an additional factor that can possibly change the amplitudes of saccades along the Müller-Lyer illusion, the center of gravity effect. It refers to the finding that the endpoints of saccades can be diverted from the target point in the direction of the center of gravity of a stimulus configuration. We measured the perceptual (adjustment method) and the action effects (amplitudes of saccades) of the illusion. In addition, we l...

Disparity sensitivity in man and owl: Psychophysical evidence for equivalent perception of shape-from-stereo

Journal of Vision Articles — Wed, 20 Jan 2010 00:00:00 +0100

In conclusion, our study establishes unprecedented experimental proof of a striking similarity in the prowess of humans and owls to achieve shape-from-stereo. (Source: Journal of Vision Articles)

A biologically plausible model of human shape symmetry perception

Journal of Vision Articles — Tue, 19 Jan 2010 00:00:00 +0100

Symmetry is usually computationally expensive to encode reliably, and yet it is relatively effortless to perceive. Here, we extend F. J. A. M. Poirier and H. R. Wilson's (2006) model for shape perception to account for H. R. Wilson and F. Wilkinson's (2002) data on shape symmetry. Because the model already accounts for shape perception, only minimal neural circuitry is required to enable it to encode shape symmetry as well. The model is composed of three main parts: (1) recovery of object position using large-scale non-Fourier V4-like concentric units that respond at the center of concentric contour segments across orientations, (2) around that recovered object center, curvature mechanisms combine multiplicatively the responses of oriented filters to encode object-centric local shape infor...

The reference frame of the tilt aftereffect

Journal of Vision Articles — Tue, 19 Jan 2010 00:00:00 +0100

Perceptual aftereffects provide a sensitive tool to investigate the influence of eye and head position on visual processing. There have been recent indications that the TAE is remapped around the time of a saccade to remain aligned to the adapting location in the world. Here, we investigate the spatial frame of reference of the TAE by independently manipulating retinal position, gaze orientation, and head orientation between adaptation and test. The results show that the critical factor in the TAE is the correspondence between the adaptation and test locations in a retinotopic frame of reference, whereas world- and head-centric frames of reference do not play a significant role. Our results confirm that adaptation to orientation takes place at retinotopic levels of visual processing. We su...

The face-in-the-crowd effect: When angry faces are just cross(es)

Journal of Vision Articles — Wed, 13 Jan 2010 00:00:00 +0100

This study aimed to discover if there might be alternative issues with schematic stimuli. The first study replicated the face-in-the-crowd threat advantage for schematic faces, but also measured a comparable effect using stimuli comprised of obliquely oriented lines. Similar results were achieved with these stimuli rotated, which had the effect of removing any residual resemblance to a face. The results suggest that low-level features probably underlie the face-in-the-crowd effect described for schematic face images, thereby undermining evidence for a search advantage for specific facial expressions. (Source: Journal of Vision Articles)

Natural cross-modal mappings between visual and auditory features

Journal of Vision Articles — Tue, 12 Jan 2010 00:00:00 +0100

The brain may combine information from different sense modalities to enhance the speed and accuracy of detection of objects and events, and the choice of appropriate responses. There is mounting evidence that perceptual experiences that appear to be modality-specific are also influenced by activity from other sensory modalities, even in the absence of awareness of this interaction. In a series of speeded classification tasks, we found spontaneous mappings between the auditory feature of pitch and the visual features of vertical location, size, and spatial frequency but not contrast. By dissociating the task variables from the features that were cross-modally related, we find that the interactions happen in an automatic fashion and are possibly located at the perceptual level. (Source: Jour...

Cue combination for 3D location judgements

Journal of Vision Articles — Tue, 12 Jan 2010 00:00:00 +0100

Cue combination rules have often been applied to the perception of surface shape but not to judgements of object location. Here, we used immersive virtual reality to explore the relationship between different cues to distance. Participants viewed a virtual scene and judged the change in distance of an object presented in two intervals, where the scene changed in size between intervals (by a factor of between 0.25 and 4). We measured thresholds for detecting a change in object distance when there were only ‘physical’ (stereo and motion parallax) or ‘texture-based’ cues (independent of the scale of the scene) and used these to predict biases in a distance matching task. Under a range of conditions, in which the viewing distance and position of the target relative to other objects was...

Parafoveal color discrimination: A chromaticity locus of enhanced discrimination

Journal of Vision Articles — Mon, 11 Jan 2010 00:00:00 +0100

Are boundaries between color categories associated with enhanced discrimination? In the present experiments, chromatic thresholds were obtained for discriminations along lines orthogonal to the yellow-blue axis of color space. The targets were parafoveal and thresholds were measured with a spatial two-alternative forced choice. In interleaved experimental runs, we also obtained empirical estimates of the subjective yellow-blue line by asking observers to categorize colors as reddish or greenish. Both types of measurement were made in the presence of a steady background that was metameric to equal-energy white. In a limited region from desaturated yellow to desaturated blue, an enhanced discrimination is found near the subjective transition between reddish and greenish hues. This line of op...

The role of co-circularity of local elements in texture perception

Journal of Vision Articles — Mon, 11 Jan 2010 00:00:00 +0100

The present study analyzes the effect of local pairwise orientation relations on the perception of textural structure. We have employed a new class of stochastic stimuli comprised of paired Gabor patches with a particular orientation difference () and relative angular position (). We measured the threshold proportion of signal pairs for discriminating the target texture from a noise texture comprised of randomly oriented pairs. The results showed that observers were sensitive not only to textures containing pairs with curvilinear configurations such as lines and curves ( = / 2), but also to their orthogonal configurations such as V shapes and parallels ( = / 2 + 90). Both classes of configuration exhibit the property of co-circularity, a fundamental geometric feature of edges and contours ...

Estimating perception of scene layout properties from global image features

Journal of Vision Articles — Fri, 08 Jan 2010 00:00:00 +0100

The relationship between image features and scene structure is central to the study of human visual perception and computer vision, but many of the specifics of real-world layout perception remain unknown. We do not know which image features are relevant to perceiving layout properties, or whether those features provide the same information for every type of image. Furthermore, we do not know the spatial resolutions required for perceiving different properties. This paper describes an experiment and a computational model that provides new insights on these issues. Humans perceive the global spatial layout properties such as dominant depth, openness, and perspective, from a single image. This work describes an algorithm that reliably predicts human layout judgments. This model's predictions...

The visual attractor illusion

Journal of Vision Articles — Fri, 08 Jan 2010 00:00:00 +0100

In many visual illusions, the perceived features of an object such as its size or orientation are influenced by nearby objects. In contrast, the presence of nearby, static objects often enhances the perceived spatial location of another object. Here we present a type of visual illusion in which the presence of a static object alters another object's perceived location. Participants localized the edge of a briefly presented and masked target object. Localization was accurate when the masked target was presented in isolation. However, when another nearby object was presented at the same time as the target, localization deviated toward the nearby object (the “attractor”). This “visual attractor illusion” was stronger when the attractor object was task-relevant rather than irrelevant a...

The relationship between CA/C ratio and individual differences in dynamic accommodative responses while viewing stereoscopic images

Journal of Vision Articles — Wed, 30 Dec 2009 00:00:00 +0100

The oculomotor synergy as expressed by the CA/C and AC/A ratios was investigated to examine its influence on our previous observation that whereas convergence responses to stereoscopic images are generally stable, some individuals exhibit significant accommodative overshoot. Using a modified video refraction unit while viewing a stereoscopic LCD, accommodative and convergence responses to balanced and unbalanced vergence and focal stimuli (BVFS and UBVFS) were measured. Accommodative overshoot of at least 0.3 D was found in 3 out of 8 subjects for UBVFS. The accommodative response differential (RD) was taken to be the difference between the initial response and the subsequent mean static steady-state response. Without overshoot, RD was quantified by finding the initial response component. ...

Effects of surrounding frame on visual search for vertical or tilted bars

Journal of Vision Articles — Tue, 29 Dec 2009 20:12:00 +0100

It is easier to find a tilted bar among vertical bars than vice-versa, but this asymmetry can be abolished or reversed by surrounding the bars with a tilted frame. The frame effect is important because it challenges bottom-up models of saliency. We conducted two experiments to investigate the causes of this effect. In Experiment 1, we removed different components of a square frame, and concluded that the frame effect was caused by a combination of (1) high-level configural cues that provided a frame of reference, and (2) bottom-up iso-orientation competition from the sides of the frame parallel to the bars. The iso-orientation competition could have arisen from (1) diversion of attention to the parts of the frame parallel to the target, or (2) iso-orientation suppression between nearby uni...

Pattern matching is assessed in retinotopic coordinates

Journal of Vision Articles — Tue, 29 Dec 2009 00:00:00 +0100

We typically examine scenes by performing multiple saccades to different objects of interest within the image. Therefore, an extra-retinotopic representation, invariant to the changes in the retinal image caused by eye movements, might be useful for high-level visual processing. We investigate here, using a matching task, whether the representation of complex natural images is retinotopic or screen-based. Subjects observed two simultaneously presented images, made a saccadic eye movement to a new fixation point, and viewed a third image. Their task was to judge whether the third image was identical to one of the two earlier images or different. Identical images could appear either in the same retinotopic position, in the same screen position, or in totally different locations. Performance ...

Top–down flow of visual spatial attention signals from parietal to occipital cortex

Journal of Vision Articles — Thu, 17 Dec 2009 09:10:00 +0100

Given the complexity of our visual environment, the ability to selectively attend to certain locations, while ignoring others, is crucial for reducing the amount of visual information to manageable levels and for optimizing behavioral performance. Sustained allocation of spatial attention causes persistent increases in functional magnetic resonance imaging (fMRI) signals in portions of early visual cortex that retinotopically represent the attended location, even in the absence of a visual stimulus. Here we test the hypothesis that topographically organized posterior parietal cortical areas IPS1 and IPS2 transmit top–down spatial attention signals to early visual cortex. We employed fMRI and coherency analysis to measure functional connectivity among cortical areas V1, V2, V3, V3A, V3B, ...

The spatial scale of perceptual memory in ambiguous figure perception

Journal of Vision Articles — Wed, 16 Dec 2009 00:00:00 +0100

Ambiguous visual stimuli highlight the constructive nature of vision: perception alternates between two plausible interpretations of unchanging input. However, when a previously viewed ambiguous stimulus reappears, its earlier perception almost entirely determines the new interpretation; memory disambiguates the input. Here, we investigate the spatial properties of this perceptual memory, taking into account strong anisotropies in percept preference across the visual field. Countering previous findings, we show that perceptual memory is not confined to the location in which it was instilled. Rather, it spreads to noncontiguous regions of the visual field, falling off at larger distances. Furthermore, this spread of perceptual memory takes place in a frame of reference that is tied to the s...

Optimal stimulus encoders for natural tasks

Journal of Vision Articles — Wed, 16 Dec 2009 00:00:00 +0100

Determining the features of natural stimuli that are most useful for specific natural tasks is critical for understanding perceptual systems. A new approach is described that involves finding the optimal encoder for the natural task of interest, given a relatively small population of noisy “neurons” between the encoder and decoder. The optimal encoder, which necessarily specifies the most useful features, is found by maximizing accuracy in the natural task, where the decoder is the Bayesian ideal observer operating on the population responses. The approach is illustrated for a patch identification task, where the goal is to identify patches of natural image, and for a foreground identification task, where the goal is to identify which side of a natural surface boundary belongs to the f...

Chromatic and luminance contrast sensitivity in fullterm and preterm infants

Journal of Vision Articles — Mon, 14 Dec 2009 00:00:00 +0100

In order to investigate the contributions of visual experience vs. preprogrammed mechanisms on visual development, the current study compared contrast sensitivity in preterm vs. fullterm infants. If development is tied to time since conception, preterm infants should match the developmental trajectories of fullterm infants when plotted in postterm age. By contrast, if development is influenced by visual experience, preterm and fullterm infants should match when plotted in postnatal age. Luminance (light/dark) and chromatic (red/green) contrast sensitivities (CS) were measured in 25 preterm (born, on average, 6.6 weeks early) and 77 fullterm infants, between 1 and 6 months postterm. In the first few months, luminance CS was found to be predicted by postterm age, suggesting that preprogramme...

Catching fly balls in virtual reality: A critical test of the outfielder problem

Journal of Vision Articles — Mon, 14 Dec 2009 00:00:00 +0100

How does a baseball outfielder know where to run to catch a fly ball? The “outfielder problem” remains unresolved, and its solution would provide a window into the visual control of action. It may seem obvious that human action is based on an internal model of the physical world, such that the fielder predicts the landing point based on a mental model of the ball's trajectory (TP). However, two alternative theories, Optical Acceleration Cancellation (OAC) and Linear Optical Trajectory (LOT), propose that fielders are led to the right place at the right time by coupling their movements to visual information in a continuous “online” manner. All three theories predict successful catches and similar running paths. We provide a critical test by using virtual reality to perturb the verti...

Edge detection and texture classification by cuttlefish

Journal of Vision Articles — Mon, 14 Dec 2009 00:00:00 +0100

Cephalopod mollusks including octopus and cuttlefish are adept at adaptive camouflage, varying their appearance to suit the surroundings. This behavior allows unique access into the vision of a non-human species because one can ask how these animals use spatial information to control their coloration pattern. There is particular interest in factors that affect the relative levels of expression of the Mottle and the Disruptive body patterns. Broadly speaking, the Mottle is displayed on continuous patterned surfaces whereas the Disruptive is used on discrete objects such as pebbles. Recent evidence from common cuttlefish, Sepia officinalis, suggests that multiple cues are relevant, including spatial scale, contrast, and depth. We analyze the body pattern responses of juvenile cuttlefish to a...

The effect of changing size on vergence is mediated by changing disparity

Journal of Vision Articles — Thu, 10 Dec 2009 18:09:00 +0100

In this study, we investigated the effect of changing size on vergence. Erkelens and Regan (1986) proposed that this cue to motion in depth affects vergence in a similar way as it affects perception. The measured effect on vergence was small and we wondered why the vergence system would use changing size as an additional cue to changing disparity. To elucidate the effect of changing size on vergence, we used an annulus carrying both changing size and changing disparity signals to motion in depth. The cues were either congruent or signaled a different depth. The results showed that vergence was affected by changing size, however in an opposite way than that perception was affected. These results were incongruent with those reported by Erkelens and Regan (1986). We therefore additionally mea...

Latitude and longitude vertical disparities

Journal of Vision Articles — Wed, 09 Dec 2009 16:53:00 +0100

We present analytical approximations for each type of vertical disparity, valid for more general conditions than previous derivations in the literature: we do not restrict ourselves to objects near the fixation point or near the plane of regard, and we allow for non-zero torsion, cyclovergence, and vertical misalignments of the eyes. We use these expressions to derive estimates of the latitude and longitude vertical disparities expected at each point in the visual field, averaged over all natural viewing. Finally, we present analytical expressions showing how binocular eye position—gaze direction, convergence, torsion, cyclovergence, and vertical misalignment—can be derived from the vertical disparity field and its derivatives at the fovea. (Source: Journal of Vision Articles)

Latitude and longitude vertical disparities

Journal of Vision Articles — Wed, 09 Dec 2009 00:00:00 +0100

Integration of monocular motion signals and the analysis of interocular velocity differences for the perception of motion-in-depth

Journal of Vision Articles — Wed, 09 Dec 2009 00:00:00 +0100

We investigated how the mechanism for perceiving motion-in-depth based on interocular velocity differences (IOVDs) integrates signals from the motion spatial frequency (SF) channels. We focused on the question whether this integration is implemented before or after the comparison of the velocity signals from the two eyes. We measured spatial frequency selectivity of the MAE of motion in depth (3D MAE). The 3D MAE showed little spatial frequency selectivity, whereas the 2D lateral MAE showed clear spatial frequency selectivity in the same condition. This indicates that the outputs of the monocular motion SF channels are combined before analyzing the IOVD. The presumption was confirmed by the disappearance of the 3D MAE after exposure to superimposed gratings with different spatial frequenci...

Dynamic information for the recognition of conversational expressions

Journal of Vision Articles — Tue, 08 Dec 2009 10:15:00 +0100

Communication is critical for normal, everyday life. During a conversation, information is conveyed in a number of ways, including through body, head, and facial changes. While much research has examined these latter forms of communication, the majority of it has focused on static representations of a few, supposedly universal expressions. Normal conversations, however, contain a very wide variety of expressions and are rarely, if ever, static. Here, we report several experiments that show that expressions that use head, eye, and internal facial motion are recognized more easily and accurately than static versions of those expressions. Moreover, we demonstrate conclusively that this dynamic advantage is due to information that is only available over time, and that the temporal integration ...

Where is the moving object now? Judgments of instantaneous position show poor temporal precision ( SD = 70 ms)

Journal of Vision Articles — Tue, 08 Dec 2009 00:00:00 +0100

Humans can precisely judge relative location between two objects moving with the same speed and direction, as numerous studies have shown. However, the precision for localizing a single moving object relative to stationary references remains a neglected topic. Here, subjects reported the perceived location of a moving object at the time of a cue. The variability of the reported positions increased steeply with the speed of the object, such that the distribution of responses corresponds to the distance that the object traveled in 70 ms. This surprisingly large temporal imprecision depends little on the characteristics of the trajectory of the moving object or of the cue that indicates when to judge the position. We propose that the imprecision reflects a difficulty in identifying which posi...

Motion-induced position shifts in global dynamic Gabor arrays

Journal of Vision Articles — Tue, 08 Dec 2009 00:00:00 +0100

Objects in motion appear shifted in space. For global motion stimuli we can ask whether the shift depends on the local or global motion. We constructed arrays of randomly oriented Gaussian enveloped drifting sine gratings (dynamic Gabors) whose speed was set such that the normal component of motion was consistent with a single global velocity. The array appears shifted in space in the direction of the global motion. The size of the shift is the same as for arrays of uniformly oriented dynamic Gabors that are moving in the same direction at the same global speed. Arrays made up of vertically oriented gratings whose speeds were set to the horizontal component of the random array elements were shifted less far. This shows that motion-induced position shifts of coherently moving surface patche...

Spatiotemporally coherent motion direction perception occurs even for spatiotemporal reversal of motion sequence

Journal of Vision Articles — Mon, 07 Dec 2009 00:00:00 +0100

Thus far, it has been pointed out that motion representation is completed in motion trajectory, and that motion representation interferes with a single physical input at a specific time and space in the motion trajectory. However, it has not been fully investigated whether the internal motion representation could interact with multiple physical inputs across time and space in motion trajectory. Thus, the current research investigated whether spatiotemporally coherent motion perception could be established in a situation involving the spatiotemporal reversal of motion sequences. In a five-point motion display, we found that the motion direction perception of the last two stimuli containing the spatiotemporal reversal was consistent with three preceding stimuli. This failure to perceive moti...

A (fascinating) litmus test for human retino- vs. non-retinotopic processing

Journal of Vision Articles — Sat, 05 Dec 2009 00:00:00 +0100

In human vision, the optics of the eye map neighboring points of the environment onto neighboring photoreceptors in the retina. This retinotopic encoding principle is preserved in the early visual areas. Under normal viewing conditions, due to the motion of objects and to eye movements, the retinotopic representation of the environment undergoes fast and drastic shifts. Yet, perceptually our environment appears stable suggesting the existence of non-retinotopic representations in addition to the well-known retinotopic ones. Here, we present a simple psychophysical test to determine whether a given visual process is accomplished in retino- or non-retinotopic coordinates. As examples, we show that visual search and motion perception can occur within a non-retinotopic frame of reference. Thes...

Binocular rivalry: Spreading dominance through complex images

Journal of Vision Articles — Sat, 05 Dec 2009 00:00:00 +0100

When different images are presented to the two eyes, each can intermittently disappear, leaving the other to dominate perception. This is called binocular rivalry. When using radial gratings, focal contrast increments can trigger a traveling wave of perceptual dominance change, originating at the locus of the contrast increment and circling the stimulus. This has been linked to a sweep of activity through V1 that can be traced via fMRI. The dominance of more complex images, like human faces, has been linked to higher level processing structures characterized by more holistic object centered properties. We therefore decided to assess how dominance would spread through more complex images. Using Kanisza squares and human faces we found that dominance tended to spread gradually away from the ...

Speed encoding in human visual cortex revealed by fMRI adaptation

Journal of Vision Articles — Thu, 03 Dec 2009 12:23:00 +0100

In macaque visual cortex, the conventional view is that image motion is initially detected by direction-sensitive neurons that are tuned in terms of local spatial and temporal frequency (TF), from which speed is encoded later. We used functional magnetic resonance imaging (fMRI) adaptation to seek evidence for speed or TF tuning in human visual cortex. Drifting sine-wave gratings were presented in pairs (S1: adapter, 100% contrast; S2: probe, 15, 40 or 80% contrast). In each trial, either speed or TF was the same for S1 and S2, whereas the other dimension changed. We investigated whether the response was weaker (adapted) for repetitions of the same speed, indicating speed coding, or for repetitions of TF, indicating TF coding. For high-contrast (80%) probes, we observed clear speed coding ...

Task influences on the dynamic properties of fast eye movements

Journal of Vision Articles — Wed, 02 Dec 2009 00:00:00 +0100

Conclusions drawn from previous studies were complicated by the fact that a subject's task influences the exact type of OKN: stare vs. look nystagmus. With our current study we set out to determine in the same subjects the exact dynamic properties (main sequence) of various forms of fast eye movements. We recorded fast phases of look and stare nystagmus as well as visually guided saccades. Our data clearly show that fast phases of look and stare nystagmus differ with respect to their main sequence. Fast phases of stare nystagmus were characterized by their lower peak velocities and longer durations as compared to fast phases of look nystagmus. Furthermore we found no differences between fast phases of stare nystagmus evoked with limited and unlimited dot lifetimes. Visually guided saccades...

Contours in noise: A role for self-cuing?

Journal of Vision Articles — Wed, 02 Dec 2009 00:00:00 +0100

A contour formed of aligned Gabor patches is easily detected amidst a dense background of randomly oriented patches; the longer the string of aligned patches, the more easily the contour is detected (D. J. Field, A. Hayes, & R. F. Hess, 1993). Here we show that a short string of collinear elements acts as a cue pointing to other patches of similar orientation that lie along the path defined by the string. Cueing might increase the gain of similarly oriented elements in the vicinity and/or reduce the number of potential locations (uncertainty) that the observer monitors. To assess the strength of the contour cue, I measured sensitivity to contrast increments on a test patch placed at various offsets relative to the cueing contour. Noise density and the length of cueing contour were also man...

Immediate transfer of synesthesia to a novel inducer

Journal of Vision Articles — Mon, 30 Nov 2009 00:00:00 +0100

In synesthesia, a certain stimulus (e.g. grapheme) is associated automatically and consistently with a stable perceptual-like experience (e.g. color). These associations are acquired in early childhood and remain robust throughout the lifetime. Synesthetic associations can transfer to novel inducers in adulthood as one learns a second language that uses another writing system. However, it is not known how long this transfer takes. We found that grapheme-color associations can transfer to novel graphemes after only a 10-minute writing exercise. Most subjects experienced synesthetic associations immediately after learning a new Glagolitic grapheme. Using a Stroop task, we provide objective evidence for the creation of novel associations between the newly learned graphemes and synesthetic col...

Stereo transparency in ambiguous stereograms generated by overlapping two identical dot patterns

Journal of Vision Articles — Mon, 30 Nov 2009 00:00:00 +0100

In binocular vision, observers can perceive transparent surfaces by fusing a stereogram composed of two overlapping patterns with different disparities. When dot patterns of two surfaces are identical, the stereogram has potential matches leading to both transparency and non-transparency (or unitary surface) perceptions. However, these two matching candidates are exclusive if the uniqueness assumption holds. This stereogram can be regarded as a random-dot version of the double-nail illusion and a stereo version of the locally paired-dot stimulus that was used to investigate the neural mechanism for motion transparency. Which surface is perceived in this ambiguous stereogram would reflect the property of the transparency detection mechanism in human stereopsis. Here we perform a parametric ...

Effect of distance upon horizontal and vertical look and stare OKN

Journal of Vision Articles — Wed, 25 Nov 2009 00:00:00 +0100

Previous reports suggest that distance influences horizontal stare OKN gains; however, the effect of distance on vertical OKN and look OKN is unknown. Horizontal and vertical look and stare OKN gains were recorded in 16 healthy volunteers (velocity 38.4°/s) at three distances (0.3 m, 1 m, and 2.5 m) and two different stimulus sizes. Asymmetry of responses and correlation of gains in different directions were compared. Measurements at near were compared with and without glasses. Distance did not significantly affect horizontal look and stare OKN or vertical look OKN, however, downward stare OKN gains were reduced at greater distances (p = 0.002). Mean downward stare OKN gains recorded in each individual were strongly correlated to leftward and rightward gains but not upward gains. In contr...

A masking analysis of glass pattern perception

Journal of Vision Articles — Wed, 25 Nov 2009 00:00:00 +0100

A Glass pattern consists of randomly distributed dot pairs (dipoles) whose orientations are determined by a geometric transform. To understand how an observer perceives the global structure, we investigated how the threshold for detecting a concentric or a radial Glass pattern (target) can be affected by the presence of another Glass pattern (masker). The Glass patterns had either concentric, radial, vertical, plaid, or spiral global forms. We used a 2AFC paradigm in which a mask was presented in both intervals while a target was randomly presented in one interval and a random dot pattern in the other. The target dot density thresholds were measured at 75% accuracy. For all masker types, the target threshold was constant at low masker densities and then increased with masker density. For c...

Oculomotor responses and visuospatial perceptual judgments compete for common limited resources

Journal of Vision Articles — Wed, 25 Nov 2009 00:00:00 +0100

While there is evidence for multiple spatial and attentional maps in the brain it is not clear to what extent visuoperceptual and oculomotor tasks rely on common neural representations and attentional mechanisms. Using a dual-task interference paradigm we tested the hypothesis that eye movements and perceptual judgments made to simultaneously presented visuospatial information compete for shared limited resources. Observers undertook judgments of stimulus collinearity (perceptual extrapolation) using a pointer and Gabor patch and/or performed saccades to a peripheral dot target while their eye movements were recorded. In addition, observers performed a non-spatial control task (contrast discrimination), matched for task difficulty and stimulus structure, which on the basis of previous stud...

Effect of accommodation on peripheral ocular aberrations

Journal of Vision Articles — Tue, 24 Nov 2009 20:30:00 +0100

Changes in peripheral aberrations, particularly higher order aberrations, as a function of accommodation have received little attention. Wavefront aberrations were measured for the right eyes of 9 young adult emmetropes at 38 field positions in the central 42 × 32 degrees of the visual field. Subjects accommodated monocularly to targets at vergences of either 0.3 or 4.0 D. Wavefront data for a 5-mm diameter pupil were analyzed either in terms of the vector components of refraction or Zernike coefficients and total RMS wavefront aberrations. Relative peripheral refractive error (RPRE) was myopic at both accommodation demands and showed only a slight, not statistically significant, hypermetropic shift in the vertical meridian with the higher accommodation demand. There was little change in ...

Face gender and emotion expression: Are angry women more like men?

Journal of Vision Articles — Tue, 24 Nov 2009 00:00:00 +0100

Certain features of facial appearance perceptually resemble expressive cues related to facial displays of emotion. We hypothesized that because expressive markers of anger (such as lowered eyebrows) overlap with perceptual markers of male sex, perceivers would identify androgynous angry faces as more likely to be a man than a woman (Study 1) and would be slower to classify an angry woman as a woman than an angry man as a man (Study 2). Conversely, we hypothesized that because perceptual features of fear (raised eyebrows) and happiness (a rounded smiling face) overlap with female sex markers, perceivers would be more likely to identify an androgynous face showing these emotions as a woman than as a man (Study 1) and would be slower to identify happy and fearful men as men than happy and fea...

Preservation of shape discrimination in aging

Journal of Vision Articles — Mon, 23 Nov 2009 21:15:00 +0100

The representation of objects becomes increasingly complex at higher levels of the human visual cortex. Shapes of intermediate complexity serve as a step in the representation of such intricate constructs. Healthy aging has adverse effects on cortical function, and we sought to determine the effects of age on the efficacy and speed of neuronal mechanisms underlying shape processing. Using deformed circular shapes, we probe object representation by varying the characteristics that define the shape and by assessing lateral interactions among shapes. Results indicate that performance declines with age for shapes defined by texture but not by luminance. However, there is no age-related slowing for the processing of shape, and probes of lateral interactions reveal spared function for complex sh...

Orientation bandwidths are invariant across spatiotemporal frequency after isotropic components are removed

Journal of Vision Articles — Mon, 23 Nov 2009 00:00:00 +0100

It is well established that mammalian visual cortex possesses a large proportion of orientation-selective neurons. Attempts to measure the bandwidth of these mechanisms psychophysically have yielded highly variable results (∼6°–180°). Two stimulus factors have been proposed to account for this variability: spatial and temporal frequency; with several studies indicating broader bandwidths at low spatial and high temporal frequencies. We estimated orientation bandwidths using a classic overlay masking paradigm across a range of spatiotemporal frequencies (0.5, 2, and 8 c.p.d.; 1.6 and 12.5 Hz) with target and mask presented either monoptically or dichoptically. A standard three-parameter Gaussian model (amplitude and width, mean fixed at 0°) confirms that bandwidths generally increase...

Monocular signals in human lateral geniculate nucleus reflect the Craik–Cornsweet–O'Brien effect

Journal of Vision Articles — Fri, 20 Nov 2009 10:10:00 +0100

The human visual system has a remarkable ability to accurately estimate the relative brightness of adjacent objects despite large variations in illumination. However, the lightness of two identical equiluminant gray regions can appear quite different when a light–dark luminance transition falls between them. This illusory brightness “filling-in” phenomenon, the Craik–Cornsweet–O'Brien (CCOB) illusion, exposes fundamental assumptions made by the visual system in estimating lightness, but its neural basis remains unclear. While the responses of high-level visual cortex can be correlated with perception of the CCOB, simple computational models suggest that the effect may originate from a much lower level, possibly subcortical. Here, we used high spatial resolution functional magneti...

Static and space-time visual saliency detection by self-resemblance

Journal of Vision Articles — Fri, 20 Nov 2009 00:00:00 +0100

We present a novel unified framework for both static and space-time saliency detection. Our method is a bottom-up approach and computes so-called local regression kernels (i.e., local descriptors) from the given image (or a video), which measure the likeness of a pixel (or voxel) to its surroundings. Visual saliency is then computed using the said “self-resemblance” measure. The framework results in a saliency map where each pixel (or voxel) indicates the statistical likelihood of saliency of a feature matrix given its surrounding feature matrices. As a similarity measure, matrix cosine similarity (a generalization of cosine similarity) is employed. State of the art performance is demonstrated on commonly used human eye fixation data (static scenes (N. Bruce & J. Tsotsos, 2006) and dyn...

Why are you angry with me? Facial expressions of threat influence perception of gaze direction

Journal of Vision Articles — Fri, 20 Nov 2009 00:00:00 +0100

Gaze direction can influence the processing of facial expressions. Angry faces are judged more angry when displaying a direct gaze compared to an averted gaze. We investigated whether facial expressions have a reciprocal influence on the perception of gaze. Participants judged the gaze of angry, fearful and neutral faces across a range of gaze directions. Angry faces were perceived as looking at the observer over a wider range than were fearful or neutral faces, which did not significantly differ. This effect was eliminated when presenting inverted faces, suggesting these results cannot be accounted for by differences in visible eye information. Our findings suggest the existence of a reciprocal influence between gaze direction and angry expressions. (Source: Journal of Vision Articles)

A summary-statistic representation in peripheral vision explains visual crowding

Journal of Vision Articles — Thu, 19 Nov 2009 00:00:00 +0100

Peripheral vision provides a less faithful representation of the visual input than foveal vision. Nonetheless, we can gain a lot of information about the world from our peripheral vision, for example in order to plan eye movements. The phenomenon of crowding shows that the reduction of information available in the periphery is not merely the result of reduced resolution. Crowding refers to visual phenomena in which identification of a target stimulus is significantly impaired by the presence of nearby stimuli, or flankers. What information is available in the periphery? We propose that the visual system locally represents peripheral stimuli by the joint statistics of responses of cells sensitive to different position, phase, orientation, and scale. This “textural” representation by sum...

The fate of task-irrelevant visual motion: Perceptual load versus feature-based attention

Journal of Vision Articles — Wed, 18 Nov 2009 22:57:00 +0100

We tested contrasting predictions derived from perceptual load theory and from recent feature-based selection accounts. Observers viewed moving, colored stimuli and performed low or high load tasks associated with one stimulus feature, either color or motion. The resultant motion aftereffect (MAE) was used to evaluate attentional allocation. We found that task-irrelevant visual features received less attention than co-localized task-relevant features of the same objects. Moreover, when color and motion features were co-localized yet perceived to belong to two distinct surfaces, feature-based selection was further increased at the expense of object-based co-selection. Load theory predicts that the MAE for task-irrelevant motion would be reduced with a higher load color task. However, this w...

Faces and text attract gaze independent of the task: Experimental data and computer model

Journal of Vision Articles — Wed, 18 Nov 2009 00:00:00 +0100

Previous studies of eye gaze have shown that when looking at images containing human faces, observers tend to rapidly focus on the facial regions. But is this true of other high-level image features as well? We here investigate the extent to which natural scenes containing faces, text elements, and cell phones—as a suitable control—attract attention by tracking the eye movements of subjects in two types of tasks—free viewing and search. We observed that subjects in free-viewing conditions look at faces and text 16.6 and 11.1 times more than similar regions normalized for size and position of the face and text. In terms of attracting gaze, text is almost as effective as faces. Furthermore, it is difficult to avoid looking at faces and text even when doing so imposes a cost. We also fo...

The role of vertical mirror symmetry in visual shape detection

Journal of Vision Articles — Wed, 18 Nov 2009 00:00:00 +0100

The goal of our study is a better understanding of the role of vertical mirror symmetry in perceptual grouping. With a simple psychophysical task and a set of controlled stimuli, we investigated whether vertical mirror symmetry acts as a cue in figure-ground segregation. We asked participants to indicate which of two sequentially presented Gabor arrays contained a visual shape. The shape was defined by a subset of Gabor elements positioned along the outline of an unfamiliar shape. By adding orientation noise to these Gabor elements, the shape percept became less salient. Across the different noise levels, symmetric shapes were easier to detect than asymmetric ones. This finding indicates that vertical mirror symmetry is indeed used as a cue in perceptual grouping. (Source: Journal of Visio...

Origin of the fast negative ERG component from isolated aspartate-treated mouse retina

Journal of Vision Articles — Tue, 17 Nov 2009 00:00:00 +0100

The leading edge of the a-wave of the ERG is generally believed to accurately reflect the changes in the circulating current through the cGMP-gated channels in the outer segment plasma membrane of rods and cones. The aspartate-isolated mammalian electroretinogram (ERG) to a rod-saturating flash contains a fast “nose”-like wave temporally overlapping with the a-wave. We characterize the nature of this nose, investigate the membrane current mechanisms involved in the nose mechanism, and propose a model that can explain the generation of the nose component in the rod inner segment. On the basis of pharmacological treatments and perfusate ion composition alterations we rule out the possible role of most of the known rod membrane current mechanisms that might participate in the generation o...

Stereoscopic discrimination of the layout of ground surfaces

Journal of Vision Articles — Tue, 17 Nov 2009 00:00:00 +0100

Safe and effective locomotion depends critically on judgements of the surface properties of the ground to be traversed. Little is known about the role of binocular vision in surface perception at distances relevant to visually guided locomotion in humans. Programmable arrays of illuminated targets were used to present sparsely textured surfaces with real depth at distances of 4.5 and 9.0 m. Psychophysical measurements of discrimination thresholds demonstrated a clear superiority for stereoscopic over monocular judgments of relative and absolute surface slant. Judgements of surface roughness in particular demonstrated a substantial binocular advantage. Binocular vision is thus shown to directly contribute to judgements of the layout of terrain up to at least 4.5 m, and its smoothness to at ...

Recalibration of multisensory simultaneity: Cross-modal transfer coincides with a change in perceptual latency

Journal of Vision Articles — Fri, 13 Nov 2009 00:00:00 +0100

After exposure to asynchronous sound and light stimuli, perceived audio-visual synchrony changes to compensate for the asynchrony. Here we investigate to what extent this audio-visual recalibration effect transfers to visual-tactile and audio-tactile simultaneity perception in order to infer the mechanisms responsible for temporal recalibration. Results indicate that audio-visual recalibration of simultaneity can transfer to audio-tactile and visual-tactile stimuli depending on the way in which the multisensory stimuli are presented. With presentation of co-located multisensory stimuli, we found a change in the perceptual latency of the visual stimuli. Presenting auditory stimuli through headphones, on the other hand, induced a change in the perceptual latency of the auditory stimuli. We a...

Categorical color constancy for simulated surfaces

Journal of Vision Articles — Thu, 12 Nov 2009 00:00:00 +0100

Color constancy is the ability to perceive constant surface colors under varying lighting conditions. Color constancy has traditionally been investigated with asymmetric matching, where stimuli are matched over two different contexts, or with achromatic settings, where a stimulus is made to appear gray. These methods deliver accurate information on the transformations of single points of color space under illuminant changes, but can be cumbersome and unintuitive for observers. Color naming is a fast and intuitive alternative to matching, allowing data collection from a large portion of color space. We asked observers to name the colors of 469 Munsell surfaces with known reflectance spectra simulated under five different illuminants. Observers were generally as consistent in naming the colo...

Latency characteristics of the short-wavelength-sensitive cones and their associated pathways

Journal of Vision Articles — Thu, 12 Nov 2009 00:00:00 +0100

There are many distinct types of retinal ganglion and LGN cells that have opponent cone inputs and which may carry chromatic information. Of interest are the asymmetries in those LGN cells that carry S-cone signals: in S-ON cells, S+ signals are opposed by (L + M) whereas, in many S-OFF cells, L+ signals are opposed by (S + M), giving −S + L − M (C. Tailby, S. G. Solomon, & P. Lennie, 2008). However, the S-opponent pathway is traditionally modeled as ±[S − (L + M)]. A phase lag of the S-cone signal has been inferred from psychophysical thresholds for discriminating combinations of simultaneous sinusoidal modulations along ±[L − M] and ±[S − (L + M)] directions (C. F. Stromeyer, R. T. Eskew, R. E. Kronauer, & L. Spillmann, 1991). We extend this experiment, measuring discriminat...

Orientation tuning of curvature adaptation reveals both curvature-polarity-selective and non-selective mechanisms

Journal of Vision Articles — Wed, 11 Nov 2009 05:10:00 +0100

We have used a curvature after-effect, or CAE, to explore whether curvature detectors are tuned for the overall orientation of a curve. CAEs were measured for half-cycle cosine-shaped contours as a function of adaptor contour orientation for a fixed test contour orientation. CAEs (i) were greatest when the adaptor and test contours had the same orientation, (ii) decreased rapidly as the orientation of the adapting contours rotated away from the test, the data being well fit by a Gaussian function with a standard deviation of 16°, (iii) increased again to a secondary peak when the adapting contours were rotated 180° relative to the test. Control experiments showed that the shape of the curvature-orientation tuning function could not be explained by local orientation adaptation, and that i...

The initial torsional Ocular Following Response (tOFR) in humans: A response to the total motion energy in the stimulus?

Journal of Vision Articles — Tue, 10 Nov 2009 07:30:00 +0100

We recorded the initial torsional ocular following responses (tOFRs) elicited at short latency by visual images that occupied the frontal plane and rotated about the lines of sight. Using 1-D radial gratings, the local spatio-temporal characteristics of these tOFRs closely resembled those we previously reported for the hOFRs to horizontal motion with 1-D vertical gratings. When the 1-D radial grating was subdivided into a number of concentric annuli, each with the same radial thickness, tOFRs were less than predicted from the sum of the responses to the individual annuli: spatial normalization. However, the normalization was much weaker than that which we previously reported for the hOFRs. Further, when the number, thickness and contrast of these concentric annuli were varied systematicall...

The sliding window of audio–visual simultaneity

Journal of Vision Articles — Tue, 10 Nov 2009 00:00:00 +0100

Humans exist in an environment wherein many unrelated events occur in close spatial and temporal proximity. Audio–visual timing experiments, however, have often examined only isolated pairs of sensory events. We therefore decided to assess how audio–visual timing perception would be shaped by the presence of an additional audio or visual event. We found that the point of subjective synchrony for a sensory event can be shifted away from the presence of other temporally proximate events. These interactions made audio–visual pairs seem unrelated, or asynchronous, at timings at which they had seemed synchronous when presented in isolation. This shows that the interval across which humans are insensitive to audio–visual asynchrony is not fixed, but dynamic, shaped by interactions betwee...

Nonlinear characterization of a simple process in human vision

Journal of Vision Articles — Fri, 06 Nov 2009 09:19:00 +0100

Perceptual processes are often modeled as linear filters followed by a decisional rule. This simple model is central to the understanding of visual processing in humans. Its scope may be extended to capture a wider range of behaviors by the addition of nonlinear operators or kernels, but there is no evidence in human sensory processing that these operators are able to enhance the linear description. We focused on a simple process in human vision, the perception of brightness in a center-surround annular stimulus. We used psychophysical reverse correlation to fully characterize this process up to its second-order nonlinearity. The resulting characterization was then used to reconstruct/predict individual responses by the human observers, a process that was significantly enhanced by the addi...

Dissociable effects of attention and crowding on orientation averaging

Journal of Vision Articles — Thu, 29 Oct 2009 23:48:00 +0100

We examined this idea in the context of an orientation averaging task, having subjects judge the mean orientation of a set of oriented signal elements either in isolation, or “crowded” by nearby randomly oriented elements. In some conditions, subjects also had to perform an attentionally demanding secondary task. By measuring performance at different levels of signal orientation variability, we show that crowding increases subjects' local uncertainty (about the orientation of individual elements) but that diverting attention reduces their global efficiency (the effective number of elements they can average over). Furthermore, performance with the same stimulus-sequence, presented multiple times, reveals that crowding does not induce more stimulus-independent variability (as would be pr...

Separate motion-detecting mechanisms for first- and second-order patterns revealed by rapid forms of visual motion priming and motion aftereffect

Journal of Vision Articles — Wed, 28 Oct 2009 20:17:00 +0100

Fast adaptation biases the perceived motion direction of a subsequently presented ambiguous test pattern (R. Kanai & F. A. Verstraten, 2005). Depending on both the duration of the adapting stimulus (ranging from tens to hundreds of milliseconds) and the duration of the adaptation-test blank interval, the perceived direction of an ambiguous test pattern can be biased towards the same or the opposite direction of the adaptation pattern, resulting in rapid forms of motion priming or motion aftereffect respectively. These findings were obtained employing drifting luminance gratings. Many studies have shown that first-order motion (luminance-defined) and second-order motion (contrast-defined) stimuli are processed by separate mechanisms. We assessed whether these effects also exist within the s...

Different cue weights at the same place

Journal of Vision Articles — Wed, 28 Oct 2009 00:00:00 +0100

The visual system uses multiple cues to estimate properties of interest. Since the errors in the estimates from different cues for the same property are generally different, a weighted average of the cues provides a better overall estimate. The most precise estimate is found when each cue's weight is proportional to its reliability. We here show that the weights given to cues for surface slant can differ between two transparent surfaces that are at the same location at the same time. Thus the weights must be assigned separately for each structure, rather than for each location. (Source: Journal of Vision Articles)

Everyone knows what is interesting: Salient locations which should be fixated

Journal of Vision Articles — Tue, 27 Oct 2009 20:11:00 +0100

Most natural scenes are too complex to be perceived instantaneously in their entirety. Observers therefore have to select parts of them and process these parts sequentially. We study how this selection and prioritization process is performed by humans at two different levels. One is the overt attention mechanism of saccadic eye movements in a free-viewing paradigm. The second is a conscious decision process in which we asked observers which points in a scene they considered the most interesting. We find in a very large participant population (more than one thousand) that observers largely agree on which points they consider interesting. Their selections are also correlated with the eye movement pattern of different subjects. Both are correlated with predictions of a purely bottom–up sali...

A new theory of structure-from-motion perception

Journal of Vision Articles — Tue, 27 Oct 2009 08:17:00 +0100

Humans can recover 3-D structure from the projected 2D motion field of a rotating object, a phenomenon called structure from motion (SFM). Current models of SFM perception are limited to the case in which objects rotate about a frontoparallel axis. However, as our recent psychophysical studies showed, frontoparallel axes of rotation are not representative of the general case. Here we present the first model to address the problem of SFM perception for the general case of rotations around an arbitrary axis. The SFM computation is cast as a two-stage process. The first stage computes the structure perpendicular to the axis of rotation. The second stage corrects for the slant of the axis of rotation. For cylinders, the computed object shape is invariant with respect to the observer's viewpoin...

Mechanisms underlying perceptual learning of contrast detection in adults with anisometropic amblyopia

Journal of Vision Articles — Tue, 27 Oct 2009 00:00:00 +0100

What underlies contrast sensitivity improvements in adults with anisometropic amblyopia following perceptual learning in grating contrast detection? In this paper, we adopted the external noise approach (Z.-L. Lu & B. A. Dosher, 1998) to identify the mechanisms underlying perceptual learning in adults with anisometropic amblyopia. By measuring contrast thresholds in a range of external noise conditions at two performance levels (79.3% and 70.7%), we found that a mixture of internal additive noise reduction and external noise exclusion underlay training induced contrast sensitivity improvements in adults with anisometropic amblyopia. In comparison, normal adults exhibited only small amount of external noise exclusion under the same training conditions. The results suggest that neural plasti...

The roles of mask luminance and perceptual grouping in visual backward masking

Journal of Vision Articles — Thu, 22 Oct 2009 23:56:00 +0100

Visual backward masking is a commonly used technique in vision research and psychology. There are two distinct types of masking. Either masking is strongest for a simultaneous presentation of the target and the mask (A-type masking) or masking is strongest when the mask trails the target (B-type masking). To account for the two types of masking, a variety of explanations have been put forward that often rely on low-level features such as the target-mask energy ratio. However, recent studies have demonstrated that the global spatial layout of the mask is an equally important factor. Here, we investigated both factors jointly. Our findings show that both factors strongly interact with each other and that neither one alone can explain the results. This finding indicates that choosing a mask s...

Tactile force perception depends on the visual speed of the collision object

Journal of Vision Articles — Wed, 21 Oct 2009 23:00:00 +0100

Previous research on the interaction between vision and touch has employed static visual and continuous tactile stimuli, and has shown that two kinds of multimodal interaction effect exist: the averaging effect and the contrast effect. The averaging effect has been used to explain several kinds of stimuli interaction while the contrast effect is associated only with the size-weight illusion (A. Charpentier, 1891). Here, we describe a novel visuotactile interaction using visual motion information that can be explained with the contrast effect. We show that the magnitude of tactile force perception (MTFP) from an impact on the palm is significantly modified by the visual motion information of a virtual collision event. Our collision simulator generates visual stimuli independently from the c...

Relative contributions of 2D and 3D cues in a texture segmentation task, implications for the roles of striate and extrastriate cortex in attentional selection

Journal of Vision Articles — Wed, 21 Oct 2009 23:00:00 +0100

In this study, we investigate whether and how 3D depth perception, believed to be processed mostly beyond V1 and starting in V2 (J. S. Bakin, K. Nakayama, & C. D. Gilbert, 2000; B. G. Cumming & A. J. Parker, 2000; F. T. Qiu & R. von der Heydt, 2005; R. von der Heydt, H. Zhou, & H. S. Friedman, 2000), contribute additionally to direct attention. We measured the reduction of the interference or the RT when the position of the texture grid for Iir was offset horizontally from that for Irel, forming an offset, 2D, stimulus. This reduction was compared with that when this positional offset was only present in the input image to one eye, or when it was in the opposite directions in the images for the two eyes, creating a 3D stimulus with a depth separation between Iir and Irel. The contribution ...

Size tuning and contextual modulation of backward contrast masking

Journal of Vision Articles — Wed, 21 Oct 2009 23:00:00 +0100

The strength of contrast masking depends not only on spatial but also on temporal parameters. In a previous study (T. P. Saarela & M. H. Herzog, 2008), we showed that the detection of a briefly presented Gabor patch is most strongly impaired when an iso-oriented grating mask immediately follows the Gabor and that this masking effect is relieved when a surround is added to the mask. Here, we studied the spatial characteristics of this backward masking effect. Gradually changing the size of the iso-oriented masking grating changes contrast detection thresholds in a non-monotonic way that can be explained in terms of contrast-dependent spatial summation and inhibition. However, these spatial interactions seem only to take place when the mask is a uniform grating. When the mask is divided into...

Attentive and pre-attentive aspects of figural processing

Journal of Vision Articles — Mon, 19 Oct 2009 19:50:00 +0100

Here we use the steady-state visual evoked potential (SSVEP) to study attentive versus non-attentive processing of simple texture-defined shapes. By “tagging” the figure and background regions with different temporal frequencies, the method isolates response components associated with the figure region, the background region, and with non-linear spatio-temporal interactions between regions. Each of these response classes has a distinct scalp topography that is preserved under differing attentional task demands. In one task, attention was directed to discrimination of shape changes in the figure region. In the other task, a difficult letter discrimination was used to divert attentive processing resources away from the texture-defined form. Larger task-dependent effects were observed for...

Orientation-tuned suppression in binocular rivalry reveals general and specific components of rivalry suppression

Journal of Vision Articles — Thu, 15 Oct 2009 23:00:00 +0100

During binocular rivalry (BR), conflicting monocular images are alternately suppressed from awareness. During suppression of an image, contrast sensitivity for probes is reduced by ~0.3–0.5 log units relative to when the image is in perceptual dominance. Previous studies on rivalry suppression have led to controversies concerning the nature and extent of suppression during BR. We tested for feature-specific suppression using orthogonal rivaling gratings and measuring contrast sensitivity to small grating probes at a range of orientations in a 2AFC orientation discrimination task. Results indicate that suppression is not uniform across orientations: suppression was much greater for orientations close to that of the suppressed grating. The higher suppression was specific to a narrow range ...

Involuntary cueing effects on accuracy measures: Stimulus and task dependence

Journal of Vision Articles — Wed, 14 Oct 2009 23:00:00 +0100

Observers reported the orientation of a tilted grating that was presented together with a vertical distractor grating. In the main experiments, target contrast was low. There was location uncertainty because target location varied randomly and differences between target and distractor were small. In contrast to a previous report (T. Liu, F. Pestilli, & M. Carrasco, 2005), our results showed that non-informative peripheral cues do not improve perceptual performance at the cued location. However, informative peripheral or central cues improved perceptual performance. When we changed the task from an unspeeded perceptual task to a speeded reaction time task, the absence of involuntary cueing effects persisted when a distractor was presented. Without distractors, involuntary cueing effects re-...

Experience-dependent changes in the topography of visual crowding

Journal of Vision Articles — Wed, 14 Oct 2009 19:11:00 +0100

The present work examined discrimination accuracy for targets that were presented either alone in the visual field (clean displays) or embedded within a dense array of letter distractors (crowded displays). The strength of visual crowding varied strongly across the four quadrants of the visual field. Furthermore, this spatial bias in crowding was strongly influenced by the observers' prior experience with specific distractor stimuli. Observers who were monolingual readers of English experienced amplified crowding in the upper-left quadrant, while subjects with primary reading skills in Korean, Chinese, or Japanese tended towards worse target discrimination in the lower visual field. This interaction with language experience was eliminated when non-alphanumeric stimuli were employed as dist...

Portraits made to measure: Manipulating social judgments about individuals with a statistical face model

Journal of Vision Articles — Tue, 13 Oct 2009 23:07:00 +0100

The social judgments people make on the basis of the facial appearance of strangers strongly affect their behavior in different contexts. However, almost nothing is known about the physical information underlying these judgments. In this article, we present a new technology (a) to quantify the information in faces that is used for social judgments and (b) to manipulate the image of a human face in a way which is almost imperceptible but changes the personality traits ascribed to the depicted person. This method was developed in a high-dimensional face space by identifying vectors that capture maximum variability in judgments of personality traits. Our method of manipulating the salience of these vectors in faces was successfully transferred to novel photographs from an independent database...

The effect of crowding on orientation-selective adaptation in human early visual cortex

Journal of Vision Articles — Tue, 13 Oct 2009 23:00:00 +0100

In this study, we combined psychophysical and fMRI adaptation techniques to search for the cortical locus of crowding. In the psychophysical experiment, when subjects' attention was controlled, we found that the threshold elevation aftereffect (TEAE) was not affected by crowding, regardless of the contrast level of adapting stimulus. In the fMRI experiment, the orientation-selective fMRI adaptation in V1 was not affected by crowding either. However, downstream from V1, we found that crowding weakened the adaptation effect in V2 and V3. Our results demonstrate that crowding occurs beyond V1 and provide one of the first pieces of direct evidence supporting the two-stage model of crowding (D. M. Levi, 2008). (Source: Journal of Vision Articles)

What is binocular vision for? A birds' eye view

Journal of Vision Articles — Tue, 13 Oct 2009 23:00:00 +0100

It is proposed that with the possible exception of owls, binocularity in birds does not have a higher order function that results in the perception of solidity and relative depth. Rather, binocularity is a consequence of the requirement of having a portion of the visual field that looks in the direction of travel; hence, each eye must have a contralateral projection that gives rise to binocularity. This contralateral projection is necessary to gain a symmetrically expanding optic flow-field about the bill. This specifies direction of travel and time to contact a target during feeding or when provisioning chicks. In birds that do not need such control of their bill, binocular field widths are very small, suggesting that binocular vision plays only a minor role in the control of locomotion. ...

Motion-aftereffect-induced blindness

Journal of Vision Articles — Mon, 12 Oct 2009 23:00:00 +0100

Motion-induced blindness (MIB) describes the occasional disappearance of salient visual objects in the presence of moving features (Y. S. Bonneh, A. Cooperman, & D. Sagi, 2001). Here we test whether motion adaptation and the ensuing motion aftereffect (MAE) are sufficient to trigger disappearance of salient targets. In three experiments, observers adapted to either rotating or static stimuli. Immediately afterwards, a static test pattern was presented consisting of a mask with texture elements and three superimposed target dots in a triangular arrangement. Observers reported dot disappearance and reappearance. The results clearly show that illusory motion in a static test pattern, following motion adaptation, promotes the disappearance of target dots. Furthermore, disappearance is modulate...

Image statistics do not explain the perception of gloss and lightness

Journal of Vision Articles — Fri, 09 Oct 2009 21:07:00 +0100

A fundamental problem in image analysis is to understand the nature of the computations and mechanisms that provide information about the material properties of surfaces. Information about a surface's 3D shape, optics, illumination field, and atmospheric conditions are conflated in the image, which must somehow be disentangled to derive the properties of surfaces. It was recently suggested that the visual system exploits some simple image statistics—histogram or sub-band skew—to infer the lightness and gloss of surfaces (I. Motoyoshi, S. Nishida, L. Sharan, & E. H. Adelson, 2007). Here, we show that the correlations Motoyoshi et al. (2007) observed between skew, lightness, and gloss only arose because of the limited space of surface geometries, reflectance properties, and illumination ...

Visual search without attentional displacement

Journal of Vision Articles — Wed, 07 Oct 2009 23:00:00 +0100

The time needed to search for an object in a complex environment increases with the number of distracting stimuli, a phenomenon known as the “set-size effect.” This observation has led to the view that, during visual search, several attentional shifts are performed, suggesting that visual information is processed serially. In an attempt to find direct evidence for such attentional shifts, we implemented several dual tasks combining a covert visual search (CVS) task or a cued target detection task with a character reporting task which allowed us to determine, a posteriori, the attentional allocation. We found that, in the cueing task, subjects preferentially reported characters displayed at different locations, demonstrating that the attention spotlight actually shifted in this conditio...

The effects of target template specificity on visual search in real-world scenes: Evidence from eye movements

Journal of Vision Articles — Tue, 06 Oct 2009 20:17:00 +0100

We can locate an object more quickly in a real-world scene when a specific target template is held in visual working memory, but it is not known exactly how a target template's specificity affects real-world search. In the present study, we compared word and picture cues in real-world scene search. Using an eye-tracker, we segmented search time into three behaviorally defined epochs: search initiation time, scanning time, and verification time. Results from three experiments indicated that target template specificity affects scanning and verification time. Within the scanning epoch, target template specificity affected the number of scene regions visited and the mean fixation duration. Changes to SOA did not affect this pattern of results. Similarly, the pattern of results did not change w...

Downhill slopes look shallower from the edge

Journal of Vision Articles — Mon, 05 Oct 2009 23:00:00 +0100

A dramatic failure of orientation constancy is documented in the perception of downhill slopes. Contrary to naïve expectation, steep downhill slopes look shallower from the edge than they do from back from the edge. Three experiments document and quantify this failure of constancy for real and virtual surfaces using a variety of dependent measures. Two additional studies document overestimation of both non-visually perceived head pitch and perceived gaze declination. A model of orientation constancy failure is fit to the data that combine exaggerations in perceived gaze declination with exaggerated scaling of perceived optical slant. These findings support a functional scale-expansion model of error in slope perception. (Source: Journal of Vision Articles)

Smooth pursuit performance during target blanking does not influence the triggering of predictive saccades

Journal of Vision Articles — Mon, 05 Oct 2009 23:00:00 +0100

Visually guided catch-up saccades during the pursuit of a moving target are highly influenced by smooth pursuit performance. For example, the decision to execute a saccade and its amplitude is driven by the difference in velocity between the eye and the target. In previous studies, we have demonstrated that the predictive saccades that occur during the blanking of the moving target compensate for the variability of the smooth pursuit response. Therefore, we wondered whether the predictive smooth pursuit response during target blanking influenced the occurrence of predictive saccades, which is the case for visually guided catch-up saccades. To answer this question, we asked subjects to track visually a target moving along a circular path. From time to time, the target was unexpectedly blank...

An object-color space

Journal of Vision Articles — Mon, 05 Oct 2009 22:03:00 +0100

Putting aside metaphorical meanings of the term, color space is understood as a vector space, where lights having the same color (i.e., subjectively indistinguishable) are represented as a point. The CIE 1931 color space, empirically based on trichromatic color measurements, is a classical example. Its derivatives, such as CIELAB and sRGB, have been successfully used in many applications (e.g., in color management). However, having been designed for presenting the color of self-luminous objects, these spaces are less suitable for presenting color of reflecting objects. Specifically, they can be used to represent color of objects only for a fixed illumination. Here I put forward a color space to represent the color of objects independently of illumination. It is based on an ideal color atla...

No capacity limit in attentional tracking: Evidence for probabilistic inference under a resource constraint

Journal of Vision Articles — Sun, 04 Oct 2009 23:00:00 +0100

Human ability to simultaneously track multiple items declines with set size. This effect is commonly attributed to a fixed limit on the number of items that can be attended to, a notion that is formalized in limited-capacity and slot models. Instead, we propose that observers are constrained by stimulus uncertainty that increases with the number of items but use Bayesian inference to achieve optimal performance. We model five data sets from published deviation discrimination experiments that varied set size, number of deviations, and magnitude of deviation. A constrained Bayesian observer better explains each data set than do the traditional limited-capacity model, the recently proposed slots-plus-averaging model, a fixed-uncertainty Bayesian model, a Bayesian model with capacity limit, an...

Accommodative and vergence responses to conflicting blur and disparity stimuli during development

Journal of Vision Articles — Sun, 04 Oct 2009 23:00:00 +0100

Accommodative and vergence responses of the typically developing visual system are generated using a combination of cues, including retinal blur and disparity. The developmental importance of blur and disparity cues in generating these motor responses was assessed by placing the two cues in conflict with each other. Cue-conflicts were induced by placing either −2 D lenses or 2 MA base-out prisms before both eyes of 140 subjects (2.0 months to 40.8 years) while they watched a cartoon movie binocularly at 80 cm. The frequency and amplitude of accommodation to lenses and vergence to prisms increased with age (both p < 0.001), with the vergence response (mean ± 1 SEM = 1.38 ± 0.05 MA) being slightly larger than the accommodative response (1.18 ± 0.04 D) at all ages (p = 0.007). The amplit...

The spatial tuning of adaptation-based time compression

Journal of Vision Articles — Thu, 01 Oct 2009 23:00:00 +0100

Temporal processing is traditionally dissociated from spatial vision. Recent evidence, however, has shown that adaptation to high temporal frequency (D. Burr, A.Tozzi, & M. C. Morrone, 2007; A. Johnston, D. H. Arnold, & S. Nishida, 2006; A. Johnston et al., 2008) induces spatially specific reductions in the apparent duration of subsecond intervals containing medium frequency drift or flicker. Here we examine the spatial tuning of these temporal adaptation effects. Our results show that duration compression is tightly tuned to the spatial location of the adaptor and can be induced by very narrow adaptors. We also demonstrate that the effects of adaptation on perceived duration are dissociable from those on apparent temporal frequency, which suggests early but separate influences of temporal...

The spatial tuning of adaption-based time compression

Journal of Vision Articles — Thu, 01 Oct 2009 23:00:00 +0100

Averaging facial expression over time

Journal of Vision Articles — Thu, 01 Oct 2009 23:00:00 +0100

The visual system groups similar features, objects, and motion (e.g., Gestalt grouping). Recent work suggests that the computation underlying perceptual grouping may be one of summary statistical representation. Summary representation occurs for low-level features, such as size, motion, and position, and even for high level stimuli, including faces; for example, observers accurately perceive the average expression in a group of faces (J. Haberman & D. Whitney, 2007, 2009). The purpose of the present experiments was to characterize the time-course of this facial integration mechanism. In a series of three experiments, we measured observers' abilities to recognize the average expression of a temporal sequence of distinct faces. Faces were presented in sets of 4, 12, or 20, at temporal freque...

Occlusion-related lateral connections stabilize kinetic depth stimuli through perceptual coupling

Journal of Vision Articles — Thu, 01 Oct 2009 08:59:00 +0100

Local sensory information is often ambiguous forcing the brain to integrate spatiotemporally separated information for stable conscious perception. Lateral connections between clusters of similarly tuned neurons in the visual cortex are a potential neural substrate for the coupling of spatially separated visual information. Ecological optics suggests that perceptual coupling of visual information is particularly beneficial in occlusion situations. Here we present a novel neural network model and a series of human psychophysical experiments that can together explain the perceptual coupling of kinetic depth stimuli with activity-driven lateral information sharing in the far depth plane. Our most striking finding is the perceptual coupling of an ambiguous kinetic depth cylinder with a coaxial...

Effects of gestational length, gender, postnatal age, and birth order on visual contrast sensitivity in infants

Journal of Vision Articles — Tue, 29 Sep 2009 23:00:00 +0100

To investigate effects of visual experience versus preprogrammed mechanisms on visual development, we used multiple regression analysis to determine the extent to which a variety of variables (that differ in the extent to which they are tied to visual experience) predict luminance and chromatic (red/green) contrast sensitivity (CS), which are mediated by the magnocellular (M) and parvocellular (P) subcortical pathways, respectively. Our variables included gestational length (GL), birth weight (BW), gender, postnatal age (PNA), and birth order (BO). Two-month-olds (n = 60) and 6-month-olds (n = 122) were tested. Results revealed that (1) at 2 months, infants with longer GL have higher luminance CS; (2) at both ages, CS significantly increases over a ~21-day range of PNA, but this effect is ...

Effects of gestational length, gender, postnatal age, and birth order on visual contrast sensitivity in infants

Journal of Vision Articles — Tue, 29 Sep 2009 23:00:00 +0100

Sensitivity and perceptual awareness increase with practice in metacontrast masking

Journal of Vision Articles — Thu, 24 Sep 2009 23:00:00 +0100

Can practice effects on unconscious stimuli lead to awareness? Can we “learn to see”? Recent evidence suggests that blindsight patients trained for an extensive period of time can learn to discriminate and consciously perceive stimuli that they were previously unaware of. So far, it is unknown whether these effects generalize to normal observers. Here we investigated practice effects in metacontrast masking. Subjects were trained for five consecutive days on the stimulus onset asynchrony (SOA) that resulted in chance performance. Our results show a linear increase in sensitivity (d′) but no change in bias (c) for the trained SOA. This practice effect on sensitivity spreads to all tested SOAs. Additionally, we show that subjects rate their perceptual awareness of the target stimuli di...

Improved classification images with sparse priors in a smooth basis

Journal of Vision Articles — Tue, 22 Sep 2009 23:00:00 +0100

Classification images provide compelling insight into the strategies used by observers in psychophysical tasks. However, because of the high-dimensional nature of classification images and the limited quantity of trials that can practically be performed, classification images are often too noisy to be useful unless denoising strategies are adopted. Here we propose a method of estimating classification images by the use of sparse priors in smooth bases and generalized linear models (GLMs). Sparse priors in a smooth basis are used to impose assumptions about the simplicity of observers' internal templates, and they naturally generalize commonly used methods such as smoothing and thresholding. The use of GLMs in this context provides a number of advantages over classic estimation techniques, ...

Intermittent occlusion enhances the smoothness of sampled motion

Journal of Vision Articles — Mon, 21 Sep 2009 18:42:00 +0100

We present evidence showing that a target in sampled motion is perceived as smoother when structure in the background appears and disappears synchronously with the target. Specifically, we found that target flicker is turned into permanent target visibility at short interstimulus intervals and jerkiness is replaced by smoothly accelerating and decelerating motion at longer ones. We argue that this “smoothening” effect is essentially a form of amodal completion in space–time being evoked by spatiotemporal cues to occlusion. The effect highlights the importance of amodal representations in perception. (Source: Journal of Vision Articles)

The role of orientation and position in shape perception

Journal of Vision Articles — Sun, 20 Sep 2009 23:00:00 +0100

This study investigates the contributions of position versus orientation information in shape perception by putting the two in conflict. Sampling the orientation of, e.g., a rounded pentagon and positioning the samples on a circle creates a stimulus in which element positions are consistent with a circle but element orientations with a pentagon.Whether orientation or position dominates the percept depends on a number of factors. First, perceived shape shows a band-pass relationship with respect to number of samples. Element orientation captures element position unless elements are widely separated or very closely spaced. This effect is scale invariant. Second, increasing element envelope size or decreasing carrier wavelength strengthens the influence of element orientation, while other par...

Myopia and peripheral ocular aberrations

Journal of Vision Articles — Sun, 20 Sep 2009 23:00:00 +0100

We measured wave aberrations over the central 42° × 32° visual field for a 5-mm pupil for groups of 10 emmetropic (mean spherical equivalent = 0.11 ± 0.50 D) and 9 myopic (MSE = −3.67 ± 1.91 D) young adults. Relative peripheral refractive errors over the measured field were generally myopic in both groups. Mean values of C40 were almost constant across the measured field and were more positive in emmetropes (+0.023 ± 0.043 μm) than in myopes (−0.007 ± 0.045 μm). Coma varied more rapidly with field angle in myopes: modeling suggested that this difference reflected the differences in mean anterior corneal shape and axial length in the two groups. In general, however, overall levels of RMS aberration differed only modestly between the two groups, implying that it is unlikely that...

The aperture problem in contoured stimuli

Journal of Vision Articles — Thu, 17 Sep 2009 05:53:00 +0100

We report that global motion integration is (a) largely insensitive to the second-order statistics of such stimuli and (b) is rigidly broadband even in the presence of a disrupted low SF component. (Source: Journal of Vision Articles)

Temporal whitening: Transient noise perceptually equalizes the 1/f temporal amplitude spectrum

Journal of Vision Articles — Tue, 15 Sep 2009 23:00:00 +0100

Naturally occurring luminance distributions are approximately 1/f in their spatial and temporal amplitude spectra. By systematically varying the spatio-temporal profile of broadband noise stimuli, we demonstrate that humans invariably overestimate the proportion of high spatial and temporal frequency energy. Critically, we find that that the strength of this bias is of a magnitude that predicts a perceptually equalized response to the spatio-temporal fall off in the natural amplitude spectrum. This interpretation is supported by our finding that the magnitude of this transient response bias, while evident across a broad range of narrowband spatial frequencies (0.25–8 cycles/deg), decreases above 2 cycles/deg, which itself compensates for the increase in temporal frequency energy previous...

Perception of limited-lifetime biological motion from different viewpoints

Journal of Vision Articles — Thu, 10 Sep 2009 23:00:00 +0100

Studies with time-limited point-lights suggested that biological motion does not require local motion detection. These studies used walkers seen from the side, but biological motion perception excels also when walkers are oriented toward the observer, or in intermediate, half-profile views. In perspective projection, the local motion of points on the body provides a cue to the 3D structure of the walker. Thus, local point motion that was irrelevant for walkers in profile view may become important for biological motion perception in perspective projection. We compared performance on forward/backward walking discrimination of walkers in orthographic and perspective projection when view orientations and with point lifetime was varied. We found no difference between orthographic and perspectiv...

The gender-specific face aftereffect is based in retinotopic not spatiotopic coordinates across several natural image transformations

Journal of Vision Articles — Thu, 10 Sep 2009 15:18:00 +0100

In four experiments, we measured the gender-specific face-aftereffect following subject's eye movement, head rotation, or head movement toward the display and following movement of the adapting stimulus itself to a new test location. In all experiments, the face aftereffect was strongest at the retinal position, orientation, and size of the adaptor. There was no advantage for the spatiotopic location in any experiment nor was there an advantage for the location newly occupied by the adapting face after it moved in the final experiment. Nevertheless, the aftereffect showed a broad gradient of transfer across location, orientation and size that, although centered on the retinotopic values of the adapting stimulus, covered ranges far exceeding the tuning bandwidths of neurons in early visual ...

Globally inconsistent figure/ground relations induced by a negative part

Journal of Vision Articles — Wed, 09 Sep 2009 23:00:00 +0100

Figure/ground interpretation is a dynamic and complex process involving the cooperation and competition of a number of perceptual factors. Most research has assumed that figure/ground assignment is globally consistent along the entire contour of a single figure, meaning that the one side of each boundary is interpreted as figure along the entire length of the boundary, and the other side interpreted as ground. We investigated a situation that challenges this assumption, because local cues to figure/ground conflict with global cues: a “negative part,” a contour region that appears locally convex but that the global form requires be concave. To measure figure/ground assignment, we use a new task based on local contour motion attribution that allows us to measure border ownership locally ...

Recruitment of a novel cue for active control depends on control dynamics

Journal of Vision Articles — Wed, 09 Sep 2009 23:00:00 +0100

We presented conditions in which an arbitrary cue (color) was coupled with task-relevant feedback (position or velocity), and measured the effect of the novel cue on performance. Participants used a joystick to keep a moving horizontal line centered on a display under velocity or acceleration control dynamics. Participants normally rely primarily on line position feedback for velocity control and line velocity feedback for acceleration control. The novel color cue was coupled with either line position (becoming red as it deviates from center) or line velocity (becoming red as it moves faster). For velocity control, performance error was smaller and response gain was larger when the novel color cue was coupled with line position than when it was coupled with line velocity. Conversely, for a...

The precision of visual working memory is set by allocation of a shared resource

Journal of Vision Articles — Tue, 08 Sep 2009 23:00:00 +0100

The mechanisms underlying visual working memory have recently become controversial. One account proposes a small number of memory “slots,” each capable of storing a single visual object with fixed precision. A contrary view holds that working memory is a shared resource, with no upper limit on the number of items stored; instead, the more items that are held in memory, the less precisely each can be recalled. Recent findings from a color report task have been taken as crucial new evidence in favor of the slot model. However, while this task has previously been thought of as a simple test of memory for color, here we show that performance also critically depends on memory for location. When errors in memory are considered for both color and location, performance on this task is in fact ...

The contributions of central versus peripheral vision to scene gist recognition

Journal of Vision Articles — Tue, 08 Sep 2009 23:00:00 +0100

Which region of the visual field is most useful for recognizing scene gist, central vision (the fovea and parafovea) based on its higher visual resolution and importance for object recognition, or the periphery, based on resolving lower spatial frequencies useful for scene gist recognition, and its large extent? Scenes were presented in two experimental conditions: a “Window,” a circular region showing the central portion of a scene, and blocking peripheral information, or a “Scotoma,” which blocks out the central portion of a scene and shows only the periphery. Results indicated the periphery was more useful than central vision for maximal performance (i.e., equal to seeing the entire image). Nevertheless, central vision was more efficient for scene gist recognition than the perip...

From disparity to depth: How to make a grating and a plaid appear in the same depth plane

Journal of Vision Articles — Fri, 04 Sep 2009 15:20:00 +0100

Even though binocular disparity is a very well-studied cue to depth, the function relating disparity and perceived depth has been characterized only for the case of horizontal disparities. We sought to determine the general relationship between disparity and depth for a particular set of stimuli. The horizontal disparity direction is a special case, albeit an especially important one. Non-horizontal disparities arise from a number of sources under natural viewing condition. Moreover, they are implicit in patterns that are one-dimensional, such as gratings, lines, and edges, and in one-dimensional components of two-dimensional patterns, where a stereo matching direction is not well-defined. What function describes perceived depth in these cases? To find out, we measured the phase disparitie...

The relationship between object spatial profile and accommodation microfluctuations in emmetropes and myopes

Journal of Vision Articles — Thu, 03 Sep 2009 23:00:00 +0100

The accommodation microfluctuations are thought to be used by the accommodation controller to obtain information about the direction and magnitude of the required response by monitoring changes in the contrast gradient of this image. The contrast gradient can be altered by presenting different spatial frequency (SF) targets to the eye. Twelve myopes (MYOs) and 12 emmetropes (EMMs) viewed sine and square wave targets of SF 0.5, 1, 2, 4, 8, 16 cpd in a Badal optical system. Accommodation responses were recorded continuously using the Shin-Nippon SRW-5000 autorefractor. There is no change in magnitude of the accommodation microfluctuations as the SF of square waves is altered. While viewing sine wave targets, the microfluctuations are smallest for mid (2, 4 cpd) SFs and increase for low (0.5 ...

Recovery of a crowded object by masking the flankers: Determining the locus of feature integration

Journal of Vision Articles — Thu, 03 Sep 2009 23:00:00 +0100

We presented a standard crowding display with a target C flanked by four flanker C's in the periphery. We then masked only the flankers (but not the target) with one of three kinds of masks—noise, metacontrast, and object substitution—each of which interferes at progressively higher levels of visual processing. With noise and metacontrast masks (low-level masking), the crowded target was recovered, whereas with object substitution masks (high-level masking), it was not. This places a clear upper bound on the locus of interference in crowding suggesting that crowding is not a low-level phenomenon. We conclude that feature integration, which underlies crowding, occurs prior to the locus of object substitution masking. Further, our results indicate that the integrity of the flankers, but ...

Contrast sensitivity in natural scenes depends on edge as well as spatial frequency structure

Journal of Vision Articles — Thu, 03 Sep 2009 23:00:00 +0100

We report that contrast sensitivity is quite different under laboratory than natural viewing conditions: adaptation or masking with natural scenes attenuates contrast sensitivity at low spatial and temporal frequencies. Expressed another way, viewing stimuli presented on homogenous screens overcomes chronic adaptation to the natural environment and causes a sharp, unnatural increase in sensitivity to low spatial and temporal frequencies. Consequently, the standard contrast sensitivity function is a poor indicator of sensitivity to structure in natural scenes. The magnitude of masking by natural scenes is relatively independent of local contrast but depends strongly on the density of edges even though neither greatly affects the local amplitude spectrum. These results suggest that sensitivi...

Accumulation of visual information across multiple fixations

Journal of Vision Articles — Thu, 03 Sep 2009 23:00:00 +0100

Humans often redirect their gaze to the same objects within a scene, even without being consciously aware of it. Here, we investigated what type of visual information is accumulated across recurrent fixations on the same object. On each trial, subjects viewed an array comprised of several objects and were subsequently asked to report on various visual aspects of a randomly chosen target object from that array. Memory performance decreased as more fixations were directed to other objects, following the last fixation on the target object (i.e. post-target fixations). In contrast, performance was enhanced with increasing number of fixations on the target object. However, since the number of post-target fixations and the number of target fixations are usually anti-correlated, memory gain may s...

Temporal constraints on conscious vision: On the ubiquitous nature of the attentional blink

Journal of Vision Articles — Sat, 29 Aug 2009 10:49:00 +0100

The attentional blink (AB) refers to the finding that observers often miss the second of two masked visual targets (T1 and T2, e.g., letters) appearing within 200–500 ms. Although the presence of a T1 mask is thought to be required for this effect, we recently found that an AB deficit can be observed even in the absence of a T1 mask if T2 is shown very briefly and followed by a pattern mask (M. R. Nieuwenstein, M. C. Potter, & J. Theeuwes, 2009). Using such a sensitive T2 task, the present study sought to determine the minimum requirements for eliciting an AB deficit. To this end, we examined if the occurrence of an AB depends on T1 exposure duration, the requirement to perform a task for T1, and awareness of T1. The results showed that an AB deficit occurs regardless of the presentation...

Different hue coding underlying figure segregation and region detection tasks

Journal of Vision Articles — Thu, 27 Aug 2009 23:00:00 +0100

Figure segregation from its background is one of the important functions of color vision for our visual system because it is a preliminary to shape recognition. However, little is known about the chromatic mechanisms underlying figure segregation as opposed to those underlying mere color discrimination and detection. We investigated whether there are differences in color difference thresholds between a shape discrimination task (involving figure segregation) and a simple region detection task. In the shape discrimination task the observer discriminated the shapes of two figures, which could be segregated from their background on the basis of a color direction (hue) difference. In the region detection task the observer simply detected a square region against its background. Thresholds of co...

Perceptual learning of global pattern motion occurs on the basis of local motion

Journal of Vision Articles — Thu, 27 Aug 2009 23:00:00 +0100

We examined whether perceptual learning of global pattern motion occurs on the basis of local or global motion as a result of performance improvement in detecting contraction (or expansion) in a display in which contracting (or expanding) dots slightly outnumbers expanding (or contracting) dots. We measured the degree of transfer of the learning effect by presenting test stimuli spatially shifted so that the region of the test stimuli partially overlapped the trained region. The results showed that the degree of transfer was entirely dependent on how similar local motion directions in the test stimuli are to those in the trained stimulus in the overlapping area, irrespective of whether a test stimulus contained the same global motion direction as the trained or not. These results indicate ...

Spatial-frequency and contrast properties of reading in central and peripheral vision

Journal of Vision Articles — Thu, 27 Aug 2009 23:00:00 +0100

In this study, we examined the effects of contrast and spatial frequency on reading speed and compared these effects between the normal fovea and periphery. We found that when text contrast was low, reading speed demonstrated spatial-frequency tuning properties, with a peak tuning frequency that partially scaled with print size. The spatial-frequency tuning disappeared when text contrast was 100%. The spatial-frequency tuning and scaling properties for reading were largely similar between the fovea and the periphery, and closely matched those for letter identification. Just as for the task of letter identification, we showed through an ideal-observer analysis that the spatial-frequency properties for reading could be primarily accounted for by the physical properties of the word stimuli co...

Temporal dynamics of saccadic distraction

Journal of Vision Articles — Thu, 27 Aug 2009 23:00:00 +0100

The saccadic distractor effect, in which irrelevant stimuli delay saccades to target stimuli, is a popular tool for investigating saccadic competition. Here, we outline the main components of a competition framework to account for the temporal dynamics of the distractor effect, inspired by race models of saccade generation. We first test a key prediction of this framework: the degree of interference should depend upon the degree of temporal overlap of target and distractor signals in the competition stage, which will vary systematically with the relative processing speeds of the competing visual signals. In agreement with this, we found that, when varying the contrast of distractor stimuli, the presentation delay between target and distractor that maximizes interference varies systematical...

Anchoring of lightness values by relative luminance and relative area

Journal of Vision Articles — Thu, 27 Aug 2009 19:19:00 +0100

Surface lightness is widely thought to depend on the relative luminance coming from neighboring surfaces. But relative luminance can produce only relative lightness values. Specific lightness values can be derived only with an anchoring rule that specifies how relative luminance values in the retinal image are mapped onto the lightness scale. We explored the anchoring rules governing very simple images consisting of two adjacent surfaces that fill the entire visual field. These were painted onto the interior of a large hemisphere that surrounded the observer's head. Lighter and darker radial sectors of the same two shades of gray were painted onto nine such hemispheres, but with different relative areas. The region of highest luminance was always seen as white. The lightness of the darker ...

The linearity and selectivity of neuronal responses in awake visual cortex

Journal of Vision Articles — Tue, 25 Aug 2009 16:41:00 +0100

Neurons in primary visual cortex (V1) are frequently classified based on their response linearity: the extent to which their visual responses to drifting gratings resemble a linear replica of the stimulus. This classification is supported by the finding that response linearity is bimodally distributed across neurons in area V1 of anesthetized animals. However, recent studies suggest that such bimodal distribution may not reflect two neuronal types but a nonlinear relationship between the membrane potential and the spike output. A main limitation of these previous studies is that they measured response linearity in anesthetized animals, where the distance between the neuronal membrane potential and the spike threshold is artificially increased by anesthesia. Here, we measured V1 response li...

The discrimination of chromatic textures

Journal of Vision Articles — Tue, 25 Aug 2009 05:15:00 +0100

Color discrimination is influenced by chromatic distributions such as they appear on differently illuminated 3D surfaces (T. Hansen, M. Giesel, & K. R. Gegenfurtner, 2008). Here, we measured discrimination thresholds for chromatically variegated stimuli and modeled the data employing a model with multiple chromatic mechanisms. Each mechanism has a differently tuned half-wave-rectified cosine-shaped sensitivity profile centered at a different chromatic direction. To estimate thresholds, the model's responses to a test and a comparison stimulus are determined. A detection variable is calculated by taking the difference of the responses to the two stimuli and by a subsequent nonlinear combination of the responses. The model was fitted to the data presented in T. Hansen et al. (2008) and to da...

Probabilistic combination of slant information: Weighted averaging and robustness as optimal percepts

Journal of Vision Articles — Sun, 23 Aug 2009 23:00:00 +0100

Depth perception involves combining multiple, possibly conflicting, sensory measurements to estimate the 3D structure of the viewed scene. Previous work has shown that the perceptual system combines measurements using a statistically optimal weighted average. However, the system should only combine measurements when they come from the same source. We asked whether the brain avoids combining measurements when they differ from one another: that is, whether the system is robust to outliers. To do this, we investigated how two slant cues—binocular disparity and texture gradients—influence perceived slant as a function of the size of the conflict between the cues. When the conflict was small, we observed weighted averaging. When the conflict was large, we observed robust behavior: perceived...

Visual motion aftereffects arise from a cascade of two isomorphic adaptation mechanisms

Journal of Vision Articles — Sun, 23 Aug 2009 23:00:00 +0100

Prolonged exposure to a moving stimulus can substantially alter the perceived velocity (both speed and direction) of subsequently presented stimuli. Here, we show that these changes can be parsimoniously explained with a model that combines the effects of two isomorphic adaptation mechanisms, one nondirectional and one directional. Each produces a pattern of velocity biases that serves as an observable “signature” of the corresponding mechanism. The net effect on perceived velocity is a superposition of these two signatures. By examining human velocity judgments in the context of different adaptor velocities, we are able to separate these two signatures. The model fits the data well, successfully predicts subjects' behavior in an additional experiment using a nondirectional adaptor, an...

Maybe they are all circles: Clues and cues

Journal of Vision Articles — Sun, 23 Aug 2009 23:00:00 +0100

This study investigates whether the weight given to image shape as a slant cue depends on the prevailing circumstances. Neither rotating an object to provide direct evidence that it is circular, nor surrounding an object with circles rather than ellipses increased the weight assigned to image shape relative to that assigned to binocular information. Thus the weight given to slant cues does not seem to rely on an elaborate analysis of the scene. (Source: Journal of Vision Articles)