Bat-Sheva Hadad

Microgenesis and Ontogenesis of Perceptual Organization Evidence From Global and Local Processing of Hierarchical Patterns

In two experiments, visual search and speeded classification were used to study perception of hierarchical patterns among participants aged 5 to 23 years. Perception of global configurations of few-element patterns and local elements of many-element patterns showed large age-related improvements. Only minor age-related changes were observed in perception of global configurations of many-element patterns and local elements of few-element patterns. These results are consistent with prior microgenetic analyses using hierarchical patterns. On the one hand, the rapid and effortless grouping of many small elements and the individuation of few large elements both mature by age 5. In contrast, the time-consuming and effortful grouping of few large elements and the individuation of many small elements improve substantially with age, primarily between ages 5 and 10. These findings support the view that perceptual organization involves multiple processes that vary in time course, attentional demands, and developmental trajectories.

Long trajectory for the development of sensitivity to global and biological motion

We used a staircase procedure to test sensitivity to (1) global motion in random-dot kinematograms moving at 4° and 18° s(-1) and (2) biological motion. Thresholds were defined as (1) the minimum percentage of signal dots (i.e. the maximum percentage of noise dots) necessary for accurate discrimination of upward versus downward motion or (2) the maximum percentage of noise dots tolerated for accurate discrimination of biological from non-biological motion. Subjects were adults and children aged 6-8, 9-11, and 12-14 years (n = 20 per group). Contrary to earlier research, results revealed a similar, long developmental trajectory for sensitivity to global motion at both slower and faster speeds and for biological motion. Thresholds for all three tasks improved monotonically between 6 and 14 years of age, at which point they were adult-like. The results suggest that the extrastriate mechanisms that integrate local motion cues over time and space take many years to mature.

Developmental trends in utilizing perceptual closure for grouping of shape: Effects of spatial proximity and collinearity

In two experiments, visual search was used to study the grouping of shape on the basis of perceptual closure among participants 5-23 years of age. We first showed that young children, like adults, demonstrate an efficient search for a concave target among convex distractors for closed connected stimuli but an inefficient search for open stimuli. Reliable developmental differences, however, were observed in search for fragmented stimuli as a function of spatial proximity and collinearity between the closureinducing fragments. When only closure was available, search for all the age groups was equally efficient for spatially close fragments and equally inefficient for spatially distant fragments. When closure and collinearity were available, search for spatially close fragments was equally efficient for all the age groups, but search for spatially distant fragments was inefficient for younger children and improved significantly between ages 5 and 10. These findings suggest that young children can utilize closure as efficiently as can adults for the grouping of shape for closed or nearly closed stimuli. When the closure inducing fragments are spatially distant, only older children and adults, but not 5-year-olds, can utilize collinearity to enhance closure for the perceptual grouping of shape.

Influence of Past Experience on Perceptual Grouping

We used primed matching to examine the microgenesis of perceptual organization for familiar (upright letters) and unfamiliar (inverted letters) visual configurations that varied in the connectedness between their line components. The configurations of upright letters were available for priming as early as 40 ms, irrespective of connectedness between their line components. The configurations of connected inverted-letter primes were also available this early, but the configurations of disconnected inverted letters were not available until later. These results show that past experience contributes to the early grouping of disconnected line segments into configurations. These findings suggest an interactive model of perceptual organization in which both image-based properties (e.g., connectedness) and input from object memories contribute to perceptual organization.

Sparing of Sensitivity to Biological Motion but Not of Global Motion after Early Visual Deprivation.

Patients deprived of visual experience during infancy by dense bilateral congenital cataracts later show marked deficits in the perception of global motion (dorsal visual stream) and global form (ventral visual stream). We expected that they would also show marked deficits in sensitivity to biological motion, which is normally processed in the superior temporal sulcus via input from both the dorsal and ventral streams. When tested on the same day for sensitivity to biological motion and to global motion at two speeds (4 and 18° s(-1)), patients, as expected, displayed a large deficit in processing global motion at both speeds. Surprisingly, they performed normally in discriminating biological motion from scrambled displays, tolerating as much noise as their age-matched controls. Networks bypassing damaged portions of the dorsal and the ventral streams must mediate the spared sensitivity to biological motion after early visual deprivation.

Motion perception: a review of developmental changes and the role of early visual experience.

Significant controversies have arisen over the developmental trajectory for the perception of global motion. Studies diverge on the age at which it becomes adult-like, with estimates ranging from as young as 3 years to as old as 16. In this article, we review these apparently conflicting results and suggest a potentially unifying hypothesis that may also account for the contradictory literature in neurodevelopmental disorders, such as Autism Spectrum Disorder (ASD). We also discuss the extent to which patterned visual input during this period is necessary for the later development of motion perception. We conclude by addressing recent studies directly comparing different types of motion integration, both in typical and atypical development, and suggest areas ripe for future research.

Time course of grouping of shape by perceptual closure: Effects of spatial proximity and collinearity

We examined time course of grouping of shape by perceptual closure in three experiments using a primed matching task. The gaps between the closure-inducing contours varied in size. In addition, depending on the distribution of the gaps along the closure-inducing contours—occurring at straight contour segments or at the point of change in contour direction—collinearity was either present or absent. In the absence of collinearity, early priming of the shape was observed for spatially close fragments, but not for spatially distant fragments. When collinearity was available, the shape of both spatially close and spatially distant fragments was primed at brief exposures. These results suggest that spatial proximity is critical for the rapid grouping of shape by perceptual closure in the absence of collinearity, but collinearity facilitates the rapid grouping of shape when the closureinducing fragments are spatially distant. In addition, shape priming persisted over time only when the collinear fragments were spatially close, suggesting that a stable representation of shape depends both on collinearity and spatial proximity between the closure-inducing fragments.

Strong Bias Towards Analytic Perception in ASD Does not Necessarily Come at the Price of Impaired Integration Skills

We first demonstrated analytic processing in ASD under conditions in which integral processing seems mandatory in TD observers, a pattern that is often taken to indicate a local default processing in ASD. However, this processing bias does not inevitably come at the price of impaired integration skills. Indeed, examining the same group of individuals with ASD on a task with explicit demands for integrated representations, Experiment 2 showed that the same observers with ASD demonstrated intact spatial integration. The results further showed that performance was not only quantitatively, but also qualitatively comparable to that of TD observers, demonstrating the sensitivity of integration in ASD to the same interactive effects of Gestalt cues.

Functional dissociation between perception and action is evident early in life

The functional distinction between vision for perception and vision for action is well documented in the mature visual system. Ganel and colleagues recently provided direct evidence for this dissociation, showing that while visual processing for perception follows Webers fundamental law of psychophysics, action violates this law. We tracked the developmental trajectory of this functional dissociation, asking whether the qualitatively different pattern observed in adults of adherence of perception but not of action to Webers law would also be evident early in life. Children aged 5-8 and adults were asked to either estimate the size of discs (perception) or grasp discs (action) varying in diameter. Interestingly, variability of perceptual estimates increased as a function of object size in accord with Webers law, while variability of grasping did not scale with object size, at all ages tested. This provides the first clear evidence for an early emergence of the dissociation between perception and action.

Sensitivity of spatial integration to perceptual cues is preserved in healthy aging

Spatial integration has been shown to substantially decline with age. We examined the mechanism underlying this age-related impairment. Young and older adults were tested on the ability to integrate contour elements across variations in the collinearity of the target elements, their spatial proximity, and the relative spacing of the target elements to the background noise elements (Δ). The results show that although contour integration generally declines with age, tolerating less noise (higher Δ) than in young adulthood, its mechanism is preserved over the years, critically depending on the relations between collinearity and spatial proximity of the contour elements. The results suggest that while spatial integration in childhood is limited by the absolute contour spacing, lacking the ability to use collinearity in order to overcome poor proximity among the elements, no changes occur in the sensitivity of contour integration to these perceptual cues at the other end of the lifespan. This suggests that the sensitivity of spatial integration to the statistics of natural scenes is preserved in aging.