People's sensitivity to content vs. formal properties of visual stimuli: Evidence from category construction.

When people are asked to classify visual stimuli, they are often insensitive to formal properties, such as their 3D coherence or symmetry. We investigated whether this pattern of formal insensitivity would also be found using more familiar stimuli and properties: paintings that differ in their artistic style and words printed in two different typefaces. The experiments used the category formation paradigm in which subjects freely sort items into groups that seem most natural to them. They could sort each stimulus set up to three times. Only about half of the subjects in Experiment 1 ever sorted the paintings by artistic style, and only 12% did so on their first sort. Only 36% ever sorted by typeface, with many of the subjects stopping after two sorts and saying that no further categories were possible. Experiment 2 repeated the test of typeface using actual words cut out of newspapers and advertisements. Half the words were printed in boldface and half not. These items lacked any strong semantic connections, yet only 30% of subjects ever sorted the items into the bold and non-bold words. The results suggest that many people are not sensitive to the formal properties of stimuli that also have semantic content. Spontaneously noticing those differences may require a particular task with explicit instructions or experience in that domain (e.g., copyeditors or art students).

Concept formation and categorization of complex, asymmetric, and impossible figures.

Impossible figures are striking examples of inconsistencies between global and local perceptual structures, in which the overall spatial configuration of the depicted image does not yield a coherent three-dimensional object. In order to investigate whether structural "impossibility" is an important perceptual property of depicted objects, we used a category formation task in which subjects were asked to divide pictures of shapes into groups that seemed most natural to them. Category formation is usually unidimensional, such that sorting is dominated by a single perceptual property, so this task can serve as a measure of which dimensions are most salient. In Experiment 1, subjects received sets of 12 line drawings consisting of six possible and six impossible objects. Very few subjects grouped the figures by impossibility on the first try, and only half did so after multiple attempts at sorting. In Experiment 2, we investigated other global properties of figures: symmetry and complexity. Subjects readily sorted objects by complexity, but seldom by symmetry. In Experiment 3, subjects were asked to draw each of the figures before sorting them, which had only a minimal effect on categorization. Finally, in Experiment 4, subjects were explicitly instructed to divide the shapes by symmetry or impossibility. Performance on this task was perfect for symmetry, but not for impossibility. Although global properties of figures seem extremely important to our perception, the results suggest that some of these cues are not immediately obvious or salient for most observers.

Oculomotor Exploration of Impossible Figures in Early Infancy.

Previous studies with young infants revealed that young infants can distinguish between displays of possible or impossible figures, which may require detection of inconsistent depth relations among local line junctions that disrupt global object configurations. Here, we used an eye-tracking paradigm to record eye movements in young infants during an object discrimination task with matched pairs of possible and impossible figures. Our goal was to identify differential patterns of oculomotor activity as infants viewed pictures of possible and impossible objects. We predicted that infants would actively attend to specific pictorial depth cues that denote shape (e.g., T-junctions), and in the context of an impossible figure that they would fixate to a greater extent in anomalous regions of the display relative to other parts. By the age of 4 months, infants fixated reliably longer overall on displays of impossible vs. possible cubes, specifically within the critical region where the incompatible lines and irreconcilable depth relations were located, implying an early capacity for selective attention to critical line junction information and integration of local depth cues necessary to perceive object coherence.

Young infants' perception of the trajectories of two- and three-dimensional objects.

We investigated oculomotor anticipations in 4-month-old infants as they viewed center-occluded object trajectories. In two experiments, we examined performance in two-dimensional (2D) and three-dimensional (3D) dynamic occlusion displays and in an additional 3D condition with a smiley face as the moving target stimulus. Rates of anticipatory eye movements were not facilitated by 3D displays or by the (presumably) more salient smiley face relative to the 2D condition. However, latencies of anticipations were reduced, implying that 3D visual information may have supported formation of more robust mental representations of the moving object. Results are interpreted in a context of perceptual constraints on developing cognitive capacities during early infancy.

Infants' Response to Pictures of Impossible Objects.

Previous work has shown that 4-month-olds can discriminate between two-dimensional (2D) depictions of structurally possible and impossible objects [S. M. Shuwairi (2009), Journal of Experimental Child Psychology, 104, 115; S. M. Shuwairi, M. K. Albert, & S. P. Johnson (2007), Psychological Science, 18, 303]. Here, we asked whether evidence of discrimination of possible and impossible pictures would also be revealed in infants' patterns of reaching and manual exploration. Nine-month-old infants were presented with realistic photograph displays of structurally possible and impossible cubes along with a series of perceptual controls, and engaged in more frequent manual exploration of pictures of impossible objects. In addition, the impossible cube display elicited significantly more social referencing and vocalizations than the possible cube and perceptual control displays. The increased manual gestures associated with the incoherent figure suggest that perceptual and manual action mechanisms are interrelated in early development. The infant's visual system extracts structural information contained in 2D images in analyzing the projected 3D configuration, and this information serves to control both the oculomotor and manual action systems.

Learning and memory facilitate predictive tracking in 4-month-olds.

We investigated 4-month-olds' oculomotor anticipations when viewing occlusion stimuli consisting of a small target that moved back and forth repetitively while the center of its trajectory was occluded by a rectangular screen. We examined performance under five conditions. In the baseline condition, infants produced few predictive relative to reactive eye movements. In the full training condition, anticipations were increased in frequency following prior exposure to a target moving along a fully visible trajectory. The delay condition tested the effects of training after a 30-min interval elapsed between training and test, resulting in a return to baseline performance. However, the training effect was reinstated in the reminder condition following another brief exposure to the training stimulus prior to test. Finally, in the brief training condition, we found that the brief exposure alone was insufficient to induce the training effect. Results are interpreted in the context of learning from short-term experience and long-term memory.

Preference for impossible figures in 4-month-olds.

Can infants use interposition and line junction cues to infer three-dimensional (3D) structure? Previous work has shown that in a task that required 4-month-olds to discriminate between static two-dimensional (2D) pictures of possible and impossible cubes, infants exhibited a spontaneous preference for displays of the impossible cube but left open the question of whether they did so on the basis of purely local "critical regions" or whether they were able to employ more global clues. Here infants were presented with possible and impossible cubes in which the strictly local cues that could have derived from exterior binding contours were deleted. Results showed that infants were still able to discriminate possible cubes from impossible cubes, suggesting that longer looking infants are sensitive to global properties and that the capacity to integrate pictorial information to perceive aspects of global 3D shape may develop earlier than demonstrated previously using reaching tasks.

Neural substrates of dynamic object occlusion.

In everyday environments, objects frequently go out of sight as they move and our view of them becomes obstructed by nearer objects, yet we perceive these objects as continuous and enduring entities. Here, we used functional magnetic resonance imaging with an attentive tracking paradigm to clarify the nature of perceptual and cognitive mechanisms subserving this ability to fill in the gaps in perception of dynamic object occlusion. Imaging data revealed distinct regions of cortex showing increased activity during periods of occlusion relative to full visibility. These regions may support active maintenance of a representation of the target's spatiotemporal properties ensuring that the object is perceived as a persisting entity when occluded. Our findings may shed light on the neural substrates involved in object tracking that give rise to the phenomenon of object permanence.

Discrimination of possible and impossible objects in infancy.

Adults can use pictorial depth cues to infer three-dimensional structure in two-dimensional depictions of objects. The age at which infants respond to the same kinds of visual information has not been determined, and theories about the underlying developmental mechanisms remain controversial. In this study, we used a visual habituation/novelty-preference procedure to assess the ability of 4-month-old infants to discriminate between two-dimensional depictions of structurally possible and impossible objects. Results indicate that young infants are sensitive to junction structures and interposition cues associated with pictorial depth and can detect inconsistent relationships among these cues that render an object impossible. Our results provide important insights into the development of mechanisms for processing pictorial depth cues that allow adults to extract three-dimensional structure from pictures of objects.

Color discrimination in schizophrenia.

Neuropsychiatric conditions that involve dopaminergic depletion have been associated with color discrimination deficits along the blue-hue (tritan, or short-wavelength-sensitive) axis. Because dopamine dysregulation may be a major factor in schizophrenia, we investigated color vision in this disorder. The performance of males with schizophrenia (SZ, n = 16) and normal male control subjects (CS, n = 14) was evaluated on five measures of color discrimination. SZ made more hue discrimination errors than CS, but no pattern emerged regarding a hue-specific axis of deficit. Dosage of anti-psychotic medication was not correlated with performance on hue discrimination. These results suggest that in medicated patients with schizophrenia, the dopaminergic disturbance, which may involve system hyperactivity, does not produce tritan-specific color deficits that have been observed in disorders involving dopaminergic hypoactivity.