Circular Stimuli Research Articles

QUEST+: A general multidimensional Bayesian adaptive psychometric method.

QUEST+ is a Bayesian adaptive psychometric testing method that allows an arbitrary number of stimulus dimensions, psychometric function parameters, and trial outcomes. It is a generalization and extension of the original QUEST procedure and incorporates many subsequent developments in the area of parametric adaptive testing. With a single procedure, it is possible to implement a wide variety of experimental designs, including conventional threshold measurement; measurement of psychometric function parameters, such as slope and lapse; estimation of the contrast sensitivity function; measurement of increment threshold functions; measurement of noise-masking functions; Thurstone scale estimation using pair comparisons; and categorical ratings on linear and circular stimulus dimensions. QUEST+ provides a general method to accelerate data collection in many areas of cognitive and perceptual science.

Cuttlefish see shape from shading, fine-tuning coloration in response to pictorial depth cues and directional illumination.

Humans use shading as a cue to three-dimensional form by combining low-level information about light intensity with high-level knowledge about objects and the environment. Here, we examine how cuttlefish Sepia officinalis respond to light and shadow to shade the white square (WS) feature in their body pattern. Cuttlefish display the WS in the presence of pebble-like objects, and they can shade it to render the appearance of surface curvature to a human observer, which might benefit camouflage. Here we test how they colour the WS on visual backgrounds containing two-dimensional circular stimuli, some of which were shaded to suggest surface curvature, whereas others were uniformly coloured or divided into dark and light semicircles. WS shading, measured by lateral asymmetry, was greatest when the animal rested on a background of shaded circles and three-dimensional hemispheres, and less on plain white circles or black/white semicircles. In addition, shading was enhanced when light fell from the lighter side of the shaded stimulus, as expected for real convex surfaces. Thus, the cuttlefish acts as if it perceives surface curvature from shading, and takes account of the direction of illumination. However, the direction of WS shading is insensitive to the directions of background shading and illumination; instead the cuttlefish tend to turn to face the light source.

Stimulus edge effects in the measurement of macular pigment using heterochromatic flicker photometry.

Heterochromatic flicker photometry (HFP) is the most common technique of measuring macular pigment optical density (MPOD). Some data strongly suggest that HFP samples MPOD specifically at the edge of center-fixated circular stimuli. Other data have led to the conclusion that HFP samples over the entire area of the stimulus. To resolve this disparity, MPOD was measured using HFP and a series of solid discs of varying radii (0.25 to 2.0 deg) and with thin annuli corresponding to the edge of those discs. MPOD assessed with the two methods yielded excellent correspondence and linearity: Y=0.01+0.98X , r=0.96. A second set of experiments showed that if a disc stimulus is adjusted for no-flicker (the standard procedure) and simply reduced in size, no flicker is observed despite the higher level of MPOD in the smaller area. Taken together, these results confirm that MPOD is determined at the edge of the measuring stimulus when using stimulus sizes in the range that is in dispute (up to a radius of 0.75 deg). The basis for this edge effect can be explained by quantitative differences in the spatial-temporal properties of the visual field as a function of angular distance from the fixation point.

Effects of animation face on skin color perception

Face perception has a unique processing pathway in the visual system. Many previous studies showed that human face skin-color was precisely reproduced, compared with other objects without facial features. Although it was shown that cartoon face yielded responses similar to those of photo images in human FFA (the fusiform face area) (Tong et al., 2000), color perception of animation faces has seldom been investigated. In this study, we aim to clarify whether and what effect animation faces have on skin-color judgment. In experiment 1, skin-color judgment was compared with stimuli between animation facial and circular images. Test stimuli consisted of 2D face, 3D face, circle and sphere with three colors of A, B and C, which (redness, blueness, luminance (cd/m2)) in the Macleod-Boynton chromaticity diagram were (0.73, 0.65, 42), (0.72, 0.75, 40) and (0.72, 0.69, 59), respectively. Ten Japanese and Korean subjects performed memory color-matching between a test stimulus and a circular stimulus of which chromaticity and luminance the subject adjusted to achieve a matching point. The standard deviation (SD) of matching color points in animation faces was bigger than in circles. In experiment 2, the effects of face-looking stimuli on skin-color judgment were examined. Test stimuli were deformed animation faces, made in five steps (from face-like to non-face like) with three colors as in experiment 1. No difference was found in SD among five steps of deformed faces. In addition, SD of the ideal skin-color (C) matching point was smaller than that of other colors (A, B) only in face stimuli of experiment 1 and 2. These results indicate that animation faces make skin-color judgment difficult compared with images without facial features. Memory skin-color could hinder precise animation skin-color judgment. Moreover, ideal skin-color could make color judgment easily on animation face images. Meeting abstract presented at VSS 2015

Brightness prediction of different sized unrelated self-luminous stimuli.

In a series of magnitude estimation experiments, the effect of the size of a circular stimulus varying from 1° to 30° field of view on the perception of brightness has been investigated for unrelated self-luminous stimuli. A clear, hue independent, size effect on brightness was found. Based on a simple modification of the recently developed Color Appearance Model CAM15u, the brightness of different sized unrelated self-luminous stimuli was adequately predicted. The modified brightness prediction performs much better than existing predictions and has been validated by a separate validation experiment.

Reaction time measurements under mesopic light levels: Towards estimation of the visual adaptation field

The definition of the visual adaptation field in night-time driving conditions is important to implement the CIE system for mesopic photometry. For this purpose, reaction times to an achromatic circular stimulus appearing at different horizontal and vertical eccentricities were measured on uniform and non-uniform backgrounds under mesopic light levels. A large screen illuminated by three projectors providing a visual field subtending 180° × 44° was used to show the background and stimuli. The results concerning both the uniform and non-uniform fields indicate that reaction times under mesopic light levels depend on the local luminance of the visual task. The location and the luminance of the stimulus and the corresponding background luminance at that point strongly affect the reaction times in mesopic conditions. Luminance distribution of the non-uniform backgrounds also affects visual performance.

Spatial limitations of fast temporal segmentation are best modeled by V1 receptive fields

The fine temporal structure of events influences the spatial grouping and segmentation of visual-scene elements. Although adjacent regions flickering asynchronously at high temporal frequencies appear identical, the visual system signals a boundary between them. These "phantom contours" disappear when the gap between regions exceeds a critical value (g(max)). We used g(max) as an index of neuronal receptive-field size to compare with known receptive-field data from along the visual pathway and thus infer the location of the mechanism responsible for fast temporal segmentation. Observers viewed a circular stimulus reversing in luminance contrast at 20 Hz for 500 ms. A gap of constant retinal eccentricity segmented each stimulus quadrant; on each trial, participants identified a target quadrant containing counterphasing inner and outer segments. Through varying the gap width, g(max) was determined at a range of retinal eccentricities. We found that g(max) increased from 0.3° to 0.8° for eccentricities from 2° to 12°. These values correspond to receptive-field diameters of neurons in primary visual cortex that have been reported in single-cell and fMRI studies and are consistent with the spatial limitations of motion detection. In a further experiment, we found that modulation sensitivity depended critically on the length of the contour and could be predicted by a simple model of spatial summation in early cortical neurons. The results suggest that temporal segmentation is achieved by neurons at the earliest cortical stages of visual processing, most likely in primary visual cortex.

P 155. Serial anodal tDCS over V1 induces long-term effects on colour discrimination in V4 measured in the unimpaired hemifield of patients with occipital stroke

Question Little is known about the impact of tDCS on higher level visual functions such as colour perception. Previous studies have primarily investigated the effects of anodal and cathodal direct current stimulation over the occipital cortex on basic visual functions (Antal and Paulus, 2008). In a recent single-session tDCS study in healthy young subjects, anodal stimulation was ineffective in transiently improving red/green discrimination (Costa, 2012). One possible explanation for this may be a ceiling effect of red/green discrimination in the healthy visual system. Given the high degree of plasticity in the sensory cortices of adults (Fahle and Poggie, 2002) we examined whether serial anodal tDCS can induce long-lasting improvements in colour discrimination in the unimpaired visual hemifield of patients with occipital stroke. Materials and methods Twelve chronic stroke patients with unilateral visual cortex lesions (mean age 54.0years, 5 male) participated in a within-subject, sham-controlled, double-blind study. MRI-registered anodal(1.5mA, 20min.)or sham tDCS was applied on 5 consecutive days above the ipsilesional calcarine sulcus. Campimetric testing of age matched colour discrimination was performed in the unaffected hemifield before and after each stimulation session and at 14-and 28-day follow-up. After a 14-day interval, an identical stimulation block with the other stimulation parameter was performed. The visual task was a forced choice task involving binocular detection of red circular stimuli, presented for 200ms in one visual field quadrant at 5° offset from fixation against a green background. Results The age matched overall deviation of colour discrimination was entered in a 2-way ANOVA. In order to control for assumable learning effects, a covariate was added to the ANOVA model. The repeated measures ANOVA attained significance for the factor stimulation ( p =0.004) (stimulation∗learning: p =0.006). The factor time reached significance by trend ( p =0.065) (time∗learning: p =0.181).No significant interaction was revealed for the factor stimulation∗time (stimulation∗time∗learning).Due to a positive learning effect post hoc tests were performed within the first block. No significant difference was seen between the baselines of anodal and sham conditions ( p =0.21).In the anodal condition colour discrimination improved compared to sham on day 5 ( p =0.045) and at two ( p =0.066) and four week ( p =0.041) follow-up. Conclusion Long-term modulation in colour perception following serial anodal tDCS may represent evidence of inducible long-term plasticity in distantly connected components of the visual system (V1 and V4) in patients with occipital stroke measured in the unimpaired hemifield. This builds on studies describing the immediate effects of tDCS in the visual system in healthy volunteers. The temporal dynamics of serial anodal tDCS seem to interact with learning processes, and may yield potential support for neuroplastic adaptation processes following cerebral lesions. Future studies should examine the long-term outcomes and dynamics of tDCS-induced neuromodulation.

Effect of different stimulus configurations on the visual evoked potential (VEP)

The purpose of this study was to assess changes in the response profile of the pattern visual evoked potential (VEP) using three stimulus configurations simulating visual-field scotomas: central circular and central blank fields increasing incrementally in diameter from 1° to 15°, hemi-field, and quadrant patterns. Five visually normal adult subjects (ages 22-68 years) were tested binocularly at 1 m for each stimulus configuration on 5 separate days. A checkerboard test pattern (64 × 64 black-and-white checks, 85% contrast, 64 cd/m(2) luminance, 20 s of stimulus duration, 2-Hz temporal frequency) was used. The group mean VEP amplitude increased in a linear manner with increase in the central circular diameter (y = 0.805x + 2.00; r = 0.986) and decrease in central blank field diameter (y = -0.769x + 16.22; r = 0.987). There was no significant change in latency in nearly all cases. The group mean coefficient of variability results indicated that the VEP amplitude was repeatable for the different stimulus configurations. The finding of VEP response linearity for the circular stimulus fields, and repeatability for all stimulus configurations, suggests that the clinician may be able to use the VEP technique with the suggested test patterns as a rapid and simple tool for objective assessment for several types of visual-field defects for a range of abnormal visual conditions and special populations.

Temporal and Spatial Dependence of Adaptation on Ganglion Cells

Author(s): Amin, Aakash; Moazzezi, Reza; Werblin, Frank | Abstract: One of the visual system’s many tasks is to be able to distinguish objects from the background. The ability to do this is limited and affected by the relationship between the object (or stimulus) of interest and the background. Adaptation in retinal neurons is the process of changing the cell’s response to a stimulus according to that stimulus’s background. When the stimulus is hard to discern from the background, the retina adapts by improving its sensitivity to low contrast. The large response range maintained by adaptation comes at a cost, however. Adaptation complicates neural coding by making the brain interpret identical stimuli as different based on differences in background. In order to further our understanding of adaptation, this study modified the background to be in terms of time and space rather than light intensity as is the norm. By changing the interval between two circular stimuli (inter-stimuli interval; IsI) of the same diameter, and by changing the diameter over a common IsI, we measured a ganglion cell’s output for one stimulus relative to another stimulus. the results show saturation (loss of output to the 2nd stimulus) of stimuli at lower IsIs. Also, the degree of saturation for a given IsI depends on the diameter of the stimulus. These combinations of results illustrate the temporal and spatial dependence of adaptation on ganglion cells. A larger-diameter stimulus involves multiple neurons surrounding the ganglion cell being recorded so various pathways most likely influence that cell’s ultimate output. Rapid stimuli (low IsI) can be defined as having large mean luminosity that directly affects ganglion cell output.

Jitter detection exceeds spatial frequency limit of the visual system

The halftone screen with fine vertical gratings is often used to modulate image in the printing technology. When the halftone screen is disturbed by the jitter in horizontal direction we observe the lattice fringe (called banding) in the horizontal direction. Surprisingly, any frequency component does not exist in the spatial frequency domain of the banding. Also, the banding is detected even when the spatial frequency of the halftone screen exceeds the frequency limit of the visual sensitivity. In this study we measured the spatial frequency properties of the halftone screen and the jitter in order to see the banding. The circular stimuli were of the vertical sinusoidal gratings with horizontal sinusoidal jitters which made on the paper with an ink-jet printer. The viewing distance was 2.5 m. The stimulus size was 6.9 degree of diameter. We varied the spatial frequency of gratings and jitters around the spatial resolution limit of the visual system as experimental parameters. The observer's task was to judge whether he saw the banding pattern in each stimulus with different jitter amplitude. The results showed that the banding was observed for the jitter amplitude of lower than 10 arc-sec in the grating with spatial frequency of less than 60 cpd. This means that the jitter amplitude threshold was in the level of hyper acuity. Also a banding pattern was observed even at the grating frequency of higher than the resolution limit. These results suggest that a nonlinear process, e.g., adaptive sampling or nonlinear function, may exist somewhere between the photoreceptor mosaic and a higher level of the visual system to yield the banding pattern.

Apparent motion distorts the shape of a stimulus briefly presented along the motion path

We examined whether motion blur accompanying apparent motion (AM) affects the shape of a stimulus presented in the motion path. In a two-alternative forced-choice procedure, observers judged the shape of a Gaussian test stimulus flashed in the path of motion, relative to a reference stimulus, which was a circular Gaussian stimulus located away from the path of motion. In Experiment 1, we report that the test stimulus was affected by AM and its perceived width was wider than its actual width, and counteracting this distortion, shape discrimination thresholds coincided with a test stimulus that was physically "thinner" than the reference stimulus. Shape distortion correlated with the strength of AM (Experiment 2) and increased within the range of inter-stimulus intervals used to induce AM and with retinal eccentricity but was eliminated when the test stimulus was made "hard-edged" (Experiment 3) or when the stimulus does not overlap with the motion path (Experiment 4). In Experiment 5, we demonstrate that the effect is present for dichoptic presentations. These results can be accounted for by a process in which the neural representation of AM generated by higher cortical areas feedback to interfere with the coding of stimulus shape by units located along the trajectory of AM.

L‐ and M‐cone input to 12Hz and 30Hz flicker ERGs across the human retina

We recorded L- and M-cone isolating ERGs from human subjects using a silent substitution technique at temporal rates of 12 and 30 Hz. These frequencies isolate the activity of cone-opponent and non-opponent post-receptoral mechanisms, respectively. ERGs were obtained using a sequence of stimuli with different spatial configurations comprising; (1) circular stimuli of different sizes which increased in 10° steps up to 70°diameter, or (2) annular stimuli with a 70° outer diameter but with different sized central ablations from 10° up to 60°. L- and M-cone isolating ERGs were obtained from five colour normal subjects using a DTL fibre electrode. Fourier analysis of the ERGs was performed and we measured the amplitude of the first harmonic of the response. For 12 Hz ERGs the L:M cone response amplitude ratio (L:M(ERG)) was close to unity and remained stable irrespective of the spatial configuration of the stimulus. The maintenance of this balanced ratio points to the existence of cone selective input across the human retina for the L-M cone opponent mechanism. For 30 Hz the L:M(ERG) ratio was greater than unity but varied depending upon which region of the retina was being stimulated. This variation we consider to be a consequence of the global response properties of M-cone ERGs rather than representing a real variation in L:M cone ratios across the retina.

Effects of visual field, exposure time, and set size on icon search with varied delays using an LCD monitor

Abstract— This study investigated the effects of visual field (left or right), exposure time, and set size on icon search with varied delay times. Nineteen women and 17 men, who were Taiwanese graduate students aged 24–40 years, participated. Participants were told to search for a target icon in a circular stimulus array, which had a diameter of 7 cm and included five, seven, or nine items. The results indicated that set size significantly affected search time. Search time was significantly longer for a nine‐icon set than for five and seven icons. Search times were significantly longer for 5‐sec delays than for 3‐and 1 ‐sec delays. However, exposure time and visual field did not significantly affect search time. Results showed that set size significantly affected accuracy. The accuracy for the five‐icon condition was greater than that for the seven‐ and nine‐icon conditions. Moreover, accuracy was greater for 1 ‐ than for 3‐ and 5‐sec‐delay conditions. However, no significant effect on accuracy was found for visual field or exposure time. Finally, search times for correct and incorrect responses were analyzed separately. The results are applicable to graphics‐based interface design.

Effects of Shape, Size, and Chromaticity of Stimuli on Estimated Size in Normally Sighted, Severely Myopic, and Visually Impaired Students

Effects of shape, size, and chromaticity of stimuli on participants' errors when estimating the size of simultaneously presented standard and comparison stimuli were examined. 48 Taiwanese college students ages 20 to 24 years old (M = 22.3, SD = 1.3) participated. Analysis showed that the error for estimated size was significantly greater for those in the low-vision group than for those in the normal-vision and severe-myopia groups. The errors were significantly greater with green and blue stimuli than with red stimuli. Circular stimuli produced smaller mean errors than did square stimuli. The actual size of the standard stimulus significantly affected the error for estimated size. Errors for estimations using smaller sizes were significantly higher than when the sizes were larger. Implications of the results for graphics-based interface design, particularly when taking account of visually impaired users, are discussed.

Correlation between Photopic Negative Response of Focal Electroretinograms and Local Loss of Retinal Neurons in Glaucoma

Purpose: To determine the relationship between the photopic negative response of the focal electroretinogram and the structural parameters of the inner retina and optic nerve head in glaucoma.Methods: Sixty-one eyes of 61 patients with open angle glaucoma, 13 eyes of 13 patients who were classified as glaucoma suspects, and 30 eyes of 30 normal subjects were studied. The focal electroretinograms were elicited by a 15° circular white stimulus on a white background centered on the fovea. The focal electroretinograms were also elicited by half of an annulus placed above or below the macula. The diameter of the inner border of the annulus was 15° and that of the outer border was 30°. The structure of the optic nerve head and retinal nerve fiber layer thickness were evaluated by scanning laser ophthalmoscopy and laser scanning polarimetry, respectively.Results: The amplitudes of the focal photopic negative responses and the ratio of the focal photopic negative response/b-wave amplitude were linearly correlated with the corresponding retinal nerve fiber layer thickness in the superior/temporal and inferior/temporal regions (r = 0.43 to 0.47; P < 0.0001) but not in the temporal region. The focal photopic negative response amplitude and focal photopic negative response/b-wave amplitude ratio were also linearly and significantly correlated with the corresponding rim areas and cup/disc area ratio (r = 0.38 to 0.50, P < 0.0001).Conclusions: These results strongly suggest that the anatomical losses of retinal neurons in local areas of the retina or optic nerve head are a cause of the reduction in the amplitude of the focal photopic negative response in open angle glaucoma.

Stimulus space topology vs. network topography in the ring model

Event Abstract Back to Event Stimulus space topology vs. network topography in the ring model The allowed patterns of activity among neurons in a recurrent network are constrained by both the structure of inputs and the structure of recurrent connections. Nevertheless, there is a growing body of evidence suggesting that, in the mature brain, patterns of spontaneous activity are similar to patterns of evoked activity, even in the absence of structured inputs. It is therefore possible that one outcome of learning is that recurrent networks serve to constrain activity patterns to be “sensible” - i.e., to reflect the same structure that is normally present during evoked activity even when the inputs are unstructured. If so, what can be inferred about connectivity in recurrent networks whose constraints reflect relations between single-cell receptive fields? We address this question in a simple class of models, in which the function of a recurrent network is to gate inputs so that only a selected set of persistent activity patterns is allowed. By “persistent activity pattern” we mean a subset of stably co-active neurons. An elegant feature of these models is that one can analytically determine the set of all stable steady states (“permitted sets”) from the synaptic matrix alone, and these activity patterns are highly constrained even when the allowed inputs are not [1]. If the allowed activity patterns are consistent with overlapping receptive fields, one can infer topological features of the underlying stimulus space [2]. This allows us to directly relate recurrent network connectivity to the topology of the represented stimulus space. We use this paradigm in an analysis of the ring model [3] for the case of unconstrained inputs. In this model, neurons are labeled by angles varying along a circle, and the strengths of recurrent connections depend only on the differences in angles between pairs of cells. If the stimulus space topology obtained from neural activity patterns simply reflected the topographic organization of the recurrent network, one would expect a circle topology for the ring model. We find instead that, depending on parameters, there are three possibilities: the topology may be either that of a point, a circle, or too complex to reflect a low-dimensional stimulus space. Only in the case of circle topology are the activity patterns consistent with the usual interpretation that individual cells have convex and overlapping receptive fields, each spanning a limited and continuous interval of angles on a circular stimulus space; this parameter regime determines preferred patterns of connectivity required for the ring model to represent a circular variable in the case of unconstrained inputs. We suggest that knowledge of the stimulus space represented by a recurrent network can provide new insights into network connectivity, even in cases where the topographic organization of the network is known. This work was supported by the Swartz Foundation and NSF DMS-0818227

Oculomotor contribution to the change in perceived speed with viewing distance

An array of moving circular stimuli was used to determine whether perceived speed is affected by the oculomotor responses associated with changes in viewing distance. The perceived speed of stimuli viewed at either 0.33 or 1.33 m was compared to the perceived speed of a similar stimulus viewed at a distance of 5.5 m. In addition, a control condition was run in which changes in perceived speed were compared for monocular viewing of the 0.33 m and 5.5 m stimuli. In the binocular condition, there were statistically significant decreases in perceived speed of about 11% for the 0.33 m viewing distance, and about 6.5% for the 1.33 m viewing distance. There was no significant decrease in perceived speed in the monocular condition. This latter finding, along with the similar appearance of the near and far stimuli in the monocular condition, suggests that ocular vergence (as opposed to accommodation or vergence-accommodation) was the primary determinant of the change in perceived speed with changes in binocular viewing distance. Although the change in perceived speed with fixation distance was relatively small, the data from all observers were in the direction of speed constancy. Thus, to the extent that vergence is a cue to egocentric distance, the present data suggest that egocentric distance is used to scale the perceived speed of targets moving at different distances from the observer.

Measurement of macular pigment optical density and distribution using the steady-state visual evoked potential

The purpose of this study was to specify isoluminance at different retinal eccentricities and to characterize macular pigment optical density (MPOD) and distribution using the steady-state visual evoked potential (VEP). Redgreen (B/G) gratings were generated within two circular stimulus fields (radius = 0.55 or 1.1 deg) and within four annular fields (maximum mean radius = 6.0 deg) on a color monitor. Temporal frequency was 15 Hz. Isoluminance was determined for each stimulus using minimum flicker photometry. Steady-state onset-offset VEPs were recorded to the same annular stimuli as the luminance ratio between adjacent chromatic components was changed from 0.25 to 0.85 in 11 automated steps (0.5 representing photometric isoluminance). Fourier analysis showed that the power of the first harmonic was minimized at the isoluminant ratio specific to each subject. Relative OD was computed by comparing the isoluminant ratio at any location with that for the most eccentric annulus. To compensate for the broadband characteristics of the monitor, OD values were corrected according to minimum flicker measurements made through known concentrations of carotenoid solution. MPOD was additionally measured using minimum motion photometry.There was high correlation between the isoluminant ratios determined by minimum flicker and VEPs for both R/G and B/G stimulation (r = 0.91, P < 0.005, slope = 1). Calibrated OD values computed from VEP estimates of B/G isoluminance correlated with those derived from minimum flicker (r = 0.96, P < 0.0005, slope = 0.85) and motion photometry (r = 0.94, P < 0.0005, slope = 0.88). OD values derived from B/G VEPs increased toward the fovea and corresponded closely with minimum flicker and minimum motion assessment of MP distribution profiles. The steady-state VEP can be used to determine isoluminance at different retinal eccentricities. MPOD and distribution can be measured by steady-state VEPs to B/G stimuli.

Altered perception of apparent motion in schizophrenia spectrum disorder

Apparent motion (AM), the Gestalt perception of motion in the absence of physical motion, was used to study perceptual organization and neurocognitive binding in schizophrenia. Associations between AM perception and psychopathology as well as meaningful subgroups were sought. Circular and stroboscopic AM stimuli were presented to 68 schizophrenia spectrum patients and healthy participants. Psychopathology was measured using the Positive and Negative Syndrome Scale (PANSS). Psychopathology was related to AM perception differentially: Positive and disorganization symptoms were linked to reduced gestalt stability; negative symptoms, excitement and depression had opposite regression weights. Dimensions of psychopathology thus have opposing effects on gestalt perception. It was generally found that AM perception was closely associated with psychopathology. No difference existed between patients and controls, but two latent classes were found. Class A members who had low levels of AM stability made up the majority of inpatients and control subjects; such participants were generally young and male, with short reaction times. Class B typically contained outpatients and some control subjects; participants in class B were older and showed longer reaction times. Hence AM perceptual dysfunctions are not specific for schizophrenia, yet AM may be a promising stage marker.