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PubMed2003

Time course of perceptual grouping by color.

Does perceptual grouping operate early or late in visual processing? One position is that the elements in perceptual layouts are grouped early in vision, by properties of the retinal image, before perceptual constancies have been determined. A second position is that perceptual grouping operates on a postconstancy representation, one that is available only after stereoscopic depth perception, lightness constancy, and amodal completion have occurred. The present experiments indicate that grouping can operate on both a preconstancy representation and a postconstancy representation. Perceptual grouping was based on retinal color similarity at short exposure durations and based on surface color similarity at long durations. These results permit an integration of the preconstancy and postconstancy positions with regard to grouping by color.

Color Perception↗
PubMed2003

Visual recognition of biological motion is impaired in children with autism.

Autistic children and typically developing control children were tested on two visual tasks, one involving grouping of small line elements into a global figure and the other involving perception of human activity portrayed in point-light animations. Performance of the two groups was equivalent on the figure task, but autistic children were significantly impaired on the biological motion task. This latter deficit may be related to the impaired social skills characteristic of autism, and we speculate that this deficit may implicate abnormalities in brain areas mediating perception of human movement.

Attention↗
PubMed1989

The effect of alcohol intoxication on primary and secondary processes in male social drinkers.

The acute effects of alcohol intoxication on cognitive style and on locus of control was investigated in an experimental setting. Sixty male subjects were randomly assigned to either an Alcohol, a Placebo, or a Control group. The alcohol dose was 1.0 ml of 100% alcohol/kg body weight. Subjects filled out a modified version of Rotter's locus of control scale and reported their perceptions to Street's Gestalt Completion Test. The latter test was scored in a standardized way for stimulus closeness, indicating a reality oriented and rational functioning, and stimulus distance, indicating a more primitive, irrational and pleasure oriented functioning. Alcohol made subjects less internally controlled and decreased the reality oriented functioning while the pleasure oriented functioning was not affected. Results were discussed in terms of pharmacological mechanisms, disinhibition, and creativity.

Adult↗
PubMed2005

Visual cognition influences early vision: the role of visual short-term memory in amodal completion.

A partly occluded visual object is perceptually filled in behind the occluding surface, a process known as amodal completion or visual interpolation. Previous research focused on the image-based properties that lead to amodal completion. In the present experiments, we examined the role of a higher-level visual process-visual short-term memory (VSTM)-in amodal completion. We measured the degree of amodal completion by asking participants to perform an object-based attention task on occluded objects while maintaining either zero or four items in visual working memory. When no items were stored in VSTM, participants completed the occluded objects; when four items were stored in VSTM, amodal completion was halted (Experiment 1). These results were not caused by the influence of VSTM on object-based attention per se (Experiment 2) or by the specific location of to-be-remembered items (Experiment 3). Items held in VSTM interfere with amodal completion, which suggests that amodal completion may not be an informationally encapsulated process, but rather can be affected by high-level visual processes.

Attention↗
PubMed1989

Alcohol effects on cognitive and personality style in women with special reference to primary and secondary process.

Changes in primary and secondary process functioning as well as in experienced locus of control as indicators of cognitive style were examined as a function of alcohol intoxication. Women subjects drank 1.0 ml of pure alcohol/kg body weight and were compared to a placebo and a control group. Results indicated a significant shift in locus of control toward greater externality and a significant shift in cognitive style from a dominance of secondary process when sober to a dominance of primary process when intoxicated. These shifts were discussed as indicative of the pharmacological properties of alcohol and were related to the disinhibition and the arousal hypotheses. Alternative explanations were also discussed.

Adult↗
PubMed1975

Effect of length, density, and angel between arms of Gestalt grouping.

In three experiments, subjects viewed two lines (arms) of dots in which one dot was shared by both arms, then judged with which arm the shared dot appeared to group. Length of an arm, density of the dots in the arm, and angle between arms were manipulated. Increasing the density of an arm increased grouping with that arm regardless of the angle between arms. Increasing the length of an arm however, increased grouping when arms met at 30 degree but not at 180 degree; intermediate angles produced intermediate effects. Advantage of the present method's simplification of the stimulus display are discussed.

Distance Perception↗
PubMed1996

Object recognition from point-light stimuli: evidence of covariation structures in conceptual representation.

Current theories of concepts and categorization involve easily identifiable attributes or features as the basic informational fodder of representation, and some composite of such features as the conceptual representation. This 'standard model' is now being questioned on a number of empirical and theoretical grounds, especially those concerning the informational origins of features. In this paper we examine the evocation of conceptual functions by point-light stimuli in which objects and constituent features are not directly given at all, but have to be constructed and construed in some way. We have maintained in previous studies that conceptual representation depends upon nested covariation hierarchies, and here suggest that the evocativeness of point-light stimuli can be explained by the structured covariation information they present. In two studies we found evidence that variation in the overall amount and the structure of covariation information in point-light stimuli is associated with variation in a number of conceptual response functions, such as the recognizability of objects from the stimuli, and the dispersion of responses. We take these results as evidence that conceptual representation depends upon, and features and other constituents are generated 'on-line' from, nested covariation hierarchies.

Adult↗
PubMed2006

Fragmented pictures revisited: long-term changes in repetition priming, relation to skill learning, and the role of cognitive resources.

BACKGROUND: Whereas age-related declines in declarative memory have been demonstrated in multiple cross-sectional and longitudinal studies, the effect of age on non-declarative manifestations of memory, such as repetition priming and perceptual skill learning, are less clear. The common assumption, based on cross-sectional studies, is that these processes are only mildly (if at all) affected by age. OBJECTIVE: To investigate long-term changes in repetition priming and age-related differences in identification of fragmented pictures in a 5-year longitudinal design. METHOD: Healthy adults (age 28-82 years) viewed drawings of objects presented in descending order of fragmentation. The identification threshold (IT) was the highest fragmentation level at which the object was correctly named. After a short interval, old pictures were presented again along with a set of similar but novel pictures. Five years later the participants repeated the experiment. RESULTS: At baseline and 5-year follow-up alike, one repeated exposure improved IT for old (priming) and new (skill acquisition) pictures. However, long-term retention of priming gains was observed only in young adults. Working memory explained a significant proportion of variance in within-occasion priming, long-term priming, and skill learning. CONCLUSION: Contrary to cross-sectional results, this longitudinal study suggests perceptual repetition priming is not an age-invariant phenomenon and advanced age and reduced availability of cognitive resources may contribute to its decline.

Adult↗
PubMed2006

The "mosaic stage" in amodal completion as characterized by magnetoencephalography responses.

We investigated the process of amodal completion in a same-different experiment in which test pairs were preceded by sequences of two figures. The first of these could be congruent to a global or local completion of an occluded part in the second figure, or a mosaic interpretation of it. We recorded and analyzed the magnetoencephalogram for the second figures. Compared to control conditions, in which unrelated primes were shown, occlusion and mosaic primes reduced the peak latency and amplitude of neural activity evoked by the occlusion patterns. Compared to occlusion primes, mosaic ones reduced the latency but increased the amplitude of evoked neural activity. Processes relating to a mosaic interpretation of the occlusion pattern, therefore, can dominate in an early stage of visual processing. The results did not provide evidence for the presence of a functional "mosaic stage" in completion per se, but characterize the mosaic interpretation as a qualitatively special one that can rapidly emerge in visual processing when context favors it.

Adult↗
PubMed2002

Is the world full of circles?

The statistical arrangement of oriented segments in natural scenes was recently proposed to be indicative of a cocircularity rule. In particular, the probability density function of the relative position of two oriented segments was found to be maximal along fixed angles on the plane, consistent with the two segments being tangent to two points of a circle. Does this observation point to a prevalence of circles in natural scenes? Here we demonstrate that similar statistics can be obtained even when circles are not very common in visual scenes. The reason is that circles or near circular objects can heavily skew the distribution in favor of the cocircularity rule.

Discrimination, Psychological↗
PubMed2003

On the principle of minimal relative motion--the bar, the circle with a dot, and the ellipse.

Beghi, Xausa, & Zanforlin (1991a) and Beghi, Xausa, De Biasio, & Zanforlin (1991b) have presented visual stereokinetic phenomena. When a bar is rotated in the image plane, it appears to be slanted in depth. Likewise, when a circle with an off-centered dot is rotated, a three-dimensional (3-D) cone is perceived. Finally, when an ellipse is rotated in the image plane, an ellipsoid is perceived that is tilted in depth. To explain these phenomena, Beghi et al. (1991a,b) offer an analytic model that assumes that the visual system nullifies the speed differences between all stimulus points. I critique this analytic model, and show that it cannot explain the perceptual phenomena.

Depth Perception↗
PubMed2006

Discrete color filling beyond luminance gaps along perceptual surfaces.

Perceived color at a point in space is not determined simply by the color directly stimulating the corresponding retinal position. Surface color is informed by flanking edge signals, which also serve to inhibit the intrusion of signals from neighboring surfaces. Spatially continuous local interactions among color and luminance signals have been implicated in a propagation process often referred to as filling-in. Here, we report a phenomenon of discrete color filling whereby color jumps over luminance gaps filling into disconnected regions of the stimulus. This color filling is found to be blocked at boundaries defined by texture. The color filling is also highly specific to the elements belonging to a common perceptual surface, even when multiple surfaces are transparently overlaid. Our results indicate that color filling can be governed by a host of visual cues outside the realm of first-order color and brightness, via their impact on perceptual surface segmentation and segregation.

Color Perception↗
PubMed2006

Constant contour integration in peripheral vision for stimuli with good Gestalt properties.

The visual system integrates discrete but aligned local stimuli to form percept of global contours. Previous experiments using "snake" contours showed that contour integration was mainly present in foveal vision but absent or greatly weakened in peripheral vision. In this study, we demonstrated that, for contour stimuli such as circles and ellipses, which bore good Gestalt properties, contour integration for shape detection and discrimination was nearly constant from the fovea to up to 35 degrees visual periphery! Contour integration was impaired by local orientation and position jitters of contour elements, indicating that the same local contour linking mechanisms revealed with snake contour stimuli also played critical roles in integration of our good Gestalt stimuli. Contour integration was also unaffected by global position jittering up to 20% of the contour size and by dramatic shape jittering, which excluded non-contour integration processes such as detection of various local cues and template matching as alternative mechanisms for uncompromised peripheral perception of good Gestalt stimuli. Peripheral contour integration also presented an interesting upper-lower visual field symmetry after asymmetries of contrast sensitivity and shape discrimination were discounted. The constant peripheral performance might benefit from easy detection of good Gestalt stimuli, which popped out from background noise, from a boost of local contour linking by top-down influences and/or from multielement contour linking by long-range interactions.

Contrast Sensitivity↗
PubMed2006

Filling-in along horizontal and vertical meridians.

PURPOSE: Filling-in is not homogeneous across the visual field; rather, fading time (FT) varies with eccentricity and polar angle. The reasons for this are unclear. The authors investigated FT along horizontal and vertical meridians in central and peripheral visual fields for luminance-defined targets, comparing Weber contrast sensitivity (CSw). They also compared cone-mediated and rod-mediated filling-in with previously described photoreceptor densities. This represents the first investigation into rod-mediated filling-in. METHODS: Fading times were recorded in nine volunteers using luminance-defined stimuli at eccentricities of 0 degrees , 2.5 degrees , 5 degrees , 10 degrees , and 20 degrees for high-contrast stimuli and 0 degrees , 1.25 degrees , 2.5 degrees , 3.75 degrees , and 5 degrees for low-contrast stimuli and were compared with CSw at each location. Fading times were also recorded at 0 degrees , 2.5 degrees , 5 degrees , 10 degrees , and 20 degrees using red-green stimuli and at 5 degrees , 10 degrees , and 20 degrees under dark-adapted conditions and compared with cone and rod densities in the nasal, temporal, superior, and inferior hemimeridians. RESULTS: Consistent anisotropy was evident in central and peripheral fields for luminance-defined targets and for chromatic targets, with horizontal meridians taking longer to fill in. The same pattern was observed in CSw and the previously described cone density. Log FT and CSw were correlated irrespective of visual field location. The ratio of rod-mediated FT to rod density decreased with eccentricity. CONCLUSIONS: Anisotropy between horizontal and vertical meridians for FT is consistent in central and peripheral fields, reflecting patterns in CSw and cone density. This is discussed in the context of cortical processes underlying filling-in. For rod-mediated filling-in, more peripheral eccentricities are characterized by reduced FTs in relation to rod density.

Adult↗