Perception of partly occluded objects in infancy

Four-month-old infants sometimes can perceive the unity of a partly hidden object. In each of a series of experiments, infants were habituated to one object whose top and bottom were visible but whose center was occluded by a nearer object. They were then tested with a fully visible continuous object and with two fully visible object pieces with a gap where the occluder had been. Patterns of dishabituation suggested that infants perceive the boundaries of a partly hidden object by analyzing the movements of its surfaces: infants perceived a connected object when its ends moved in a common translation behind the occluder. Infants do not appear to perceive a connected object by analyzing the colors and forms of surfaces: they did not perceive a connected object when its visible parts were stationary, its color was homogeneous, its edges were aligned, and its shape was simple and regular. These findings do not support the thesis, from gestalt psychology, that object perception first arises as a consequence of a tendency to perceive the simplest, most regular configuration, or the Piagetian thesis that object perception depends on the prior coordination of action. Perception of objects may depend on an inherent conception of what an object is.     

Conditions for young infants' failure to perceive trajectory continuity

When viewing an event in which an object moves behind an occluder on part of its trajectory, 4-month-old infants perceive the trajectory as continuous only when time or distance out of sight is short. Little is known, however, about the conditions under which young infants perceive trajectories to be discontinuous. In the present studies we focus first on infants' perception of trajectories that change during a period of occlusion. Four-month-olds perceive discontinuity in trajectories that change in height or orientation while behind an occluder, and this is true even when a change in direction could be due to an invisible bouncing collision with a surface. Further experiments reveal that infants do not perceive diagonal linear trajectories as continuous across an occlusion unless the occluding and revealing edges are orthogonal to the path of movement. Implications for theories of perceptual and cognitive development are discussed.     

Eye tracking provides no evidence that young infants understand path obstruction

In two experiments with 47 4-month-olds, we investigated attention to key aspects of events in which an object moved along a partly occluded path that contained an obstruction. Infants were familiarized with a ball rolling behind an occluder to be revealed resting on an end wall, and on test trials an obstruction wall was placed in the ball's path. In Experiment 1, we did not find longer looking when the object appeared in an impossible location beyond the obstruction, and infants did not selectively fixate the object in this location. In Experiment 2, after rolling one or two balls, we measured infants' fixations of a two-object outcome with one ball in a novel but possible resting position and the other in a familiar but impossible location beyond the obstruction. Infants looked longer at the ball in the possible but novel location, likely reflecting a looking preference for location novelty. Thus we obtained no evidence that infants reasoned about obstruction and identified a violation on that basis.     

Young infants' reasoning about hidden objects: evidence from violation-of-expectation tasks with test trials only

The present research examined alternative accounts of prior violation-of-expectation (VOE) reports that young infants can represent and reason about hidden objects. According to these accounts, young infants' apparent success in these VOE tasks reflects only novelty and familiarity preferences induced by the habituation or familiarization trials in the tasks. In two experiments, 4-month-old infants were tested in VOE tasks with test trials only. The infants still gave evidence that they could represent and reason about hidden objects: they were surprised, as indicated by greater attention, when a wide object became fully hidden behind a narrow occluder (Experiment 1) or inside a narrow container (Experiment 2). These and control results demonstrate that young infants can succeed at VOE tasks involving hidden objects even when given no habituation or familiarization trials. The present research thus provides additional support for the conclusion that young infants possess expectations about hidden objects. Methodological issues concerning the use of habituation or familiarization trials in VOE tasks are also discussed.     

Motion and edge sensitivity in perception of object unity

Although much evidence indicates that young infants perceive unitary objects by analyzing patterns of motion, infants' abilities to perceive object unity by analyzing Gestalt properties and by integrating distinct views of an object over time are in dispute. To address these controversies, four experiments investigated adults' and infants' perception of the unity of a center-occluded, moving rod with misaligned visible edges. Both alignment information and depth information affected adults' and infants' perception of object unity in similar ways, and infants perceived object unity by integrating information about object features over time. However, infants perceived a moving, misaligned, three-dimensional object as indeterminate in its connectedness, whereas adults perceived it as connected behind the occluder. These findings indicate that the effectiveness of common motion in specifying unified surfaces across an occluder is reduced by misalignment of edges. Alignment information enhances perception of object unity either by serving directly as information for unity or by optimizing the detectability of motion-carried information for unity. In addition, young infants are able to retain information about edge orientation over short intervals in determining connectedness via a process of spatiotemporal integration.     

The emergence of kind-based object individuation in infancy

Four experiments investigated whether 12-month-old infants use perceptual property information in a complex object individuation task, using the violation-of-expectancy looking time method (Xu, 2002; Xu & Carey, 1996). Infants were shown two objects with different properties emerge and return behind an occluder, one at a time. The occluder was then removed, revealing either two objects (expected outcome, if property differences support individuation) or one object (unexpected outcome). In Experiments 1-3, infants failed to use color, size, or a combination of color, size, and pattern differences to establish a representation of two distinct objects behind an occluder. In Experiment 4, infants succeeded in using cross-basic-level-kind shape differences to establish a representation of two objects but failed to do so using within-basic-level-kind shape differences. Control conditions found that the methods were sensitive. Infants succeeded when provided unambiguous spatiotemporal information for two objects, and they encoded the property differences during these experiments. These findings suggest that by 12 months, different properties play different roles in a complex object individuation task. Certain salient shape differences enter into the computation of numerical distinctness of objects before other property differences such as color or size. Since shape differences are often correlated with object kind differences, these results converge with others in the literature that suggest that by the end of the first year of life, infants' representational systems begin to distinguish kinds and properties.     

The role of good form in young Infants' perception of partly occluded objects

Young infants have been reported to perceive the unity of a center-occluded object when the visible ends of the object undergo common motion, but not on the basis of stationary information (e.g., P. J. Kellman & E. S. Spelke, 1983). We investigated the possibility that 4-month-old infants will attend to and utilize the global configuration (i.e., the "good form") of a partly occluded, moving object to perceive its unity and coherence behind the occluder. In the first experiment, infants viewed a partly occluded circle or cross that translated laterally. Infants who habituated in the minimum number of trials ("fast habituators") showed a reliable posthabituation preference for a broken object over a complete object, indicating perception of unity in the habituation display. Slow habituators exhibited no posthabituation preference. In the second experiment, infants were presented with small ring and cross displays, and the infants looked longer at the broken object. There were no reliable differences in performance between fast and slow habituators. A control group demonstrated no reliable posthabituation preference. In three additional conditions, infants viewed either a partly occluded half ring or a display in which two rod parts were either relatable and nonaligned or nonrelatable. The results indicated that curvature per se provided information in support of completion, in addition to global configuration and motion. Implications for theories of infants' visual development are discussed.     

Infants' representations of three-dimensional occluded objects

Infants' ability to represent objects has received significant attention from the developmental research community. With the advent of eye-tracking technology, detailed analysis of infants' looking patterns during object occlusion have revealed much about the nature of infants' representations. The current study continues this research by analyzing infants' looking patterns in a novel manner and by comparing infants' looking at a simple display in which a single three-dimensional (3D) object moves along a continuous trajectory to a more complex display in which two 3D objects undergo trajectories that are interrupted behind an occluder. Six-month-old infants saw an occlusion sequence in which a ball moved along a linear path, disappeared behind a rectangular screen, and then a ball (ball-ball event) or a box (ball-box event) emerged at the other edge. An eye-tracking system recorded infants' eye-movements during the event sequence. Results from examination of infants' attention to the occluder indicate that during the occlusion interval infants looked longer to the side of the occluder behind which the moving occluded object was located, shifting gaze from one side of the occluder to the other as the object(s) moved behind the screen. Furthermore, when events included two objects, infants attended to the spatiotemporal coordinates of the objects longer than when a single object was involved. These results provide clear evidence that infants' visual tracking is different in response to a one-object display than to a two-object display. Furthermore, this finding suggests that infants may require more focused attention to the hidden position of objects in more complex multiple-object displays and provides additional evidence that infants represent the spatial location of moving occluded objects.     

Precursors to the development of intention at 6 months: understanding people and their actions

Under investigation was whether 6-month-old infants expect people to behave differently toward persons and inanimate objects. Infants were randomly assigned to experimental and control conditions. In the experimental conditions, infants were habituated to an actor who either talked to or reached for and swiped with something hidden behind an occluder. In the test events the actor was occluded, but the infants were shown either a person or an object. In the control condition, infants only saw the person or object stimulus. Results showed that infants who had been habituated to an actor who was talking looked longer at the object, and infants who had been habituated to an actor who was reaching and swiping looked longer at the person. No difference in looking at the stimuli was observed in the control condition. This suggests that infants expect people's actions to be related to objects in ways that are continuous with more mature, intentional understandings.     

The spread of attention to hidden portions of occluded surfaces

We report two experiments in which the two-rectangles method of Egly, Driver, and Rafal (1994) was used to test whether object-specific attentional cuing advantages can spread to hidden portions of occluded objects. Displays began with portions of two rectangles hidden by a third, occluding object. One end of one of the two rectangles was cued, after which the occluder rotated around its center point and target stimuli were presented. In one condition, the occluder was removed from in front of the other objects, either by rotating away from them (Experiment 1B) or by rotating and then slipping behind them (Experiment 1B). In another condition, the occluder first rotated away but then returned to its original position. In both experiments, an object-specific cuing advantage occurred in the occluderremoved condition for targets that appeared in what had been hidden locations of the cued object. No analogous advantage occurred in the occluder-returned condition.     

Nine‐ to 11‐month‐old infants' reasoning about causality in anomalous human movements1

Two habituation experiments investigated 9–11‐month‐old infants' reasoning about causality in anomalous human movements. During habituation, infants saw an event in which a person walked toward a stationary person behind an occluder who fell down after an interval. Then, the infants were tested with two events without the occluder: the contact event in which the first person pushed the second one to fall down and the no‐contact event in which the second person fell down without any contact. In Experiment 1, in which the persons were face‐to‐back, infants looked at the no‐contact event for a longer time, whereas in Experiment 2, in which the persons were face‐to‐face, they looked at both the events for equal duration. Thus, infants considered it unnatural when a person fell down without external force in the absence of any action from a distance (e.g. communication). Infants seem to apply the physical contact principles to human movements in certain cases.     

Perception of occlusion by young infants: Must the occlusion event be congruent with the occluder?

Four-month-old infants perceive continuity of an object’s trajectory through occlusion, even when the occluder is illusory, and several cues are apparently needed for young infants to perceive a veridical occlusion event. In this paper we investigated the effects of dislocating the spatial relation between the occlusion events and the visible edges of the occluder. In two experiments testing 60 participants, we demonstrated that 4-month-olds do not perceive continuity of an object’s trajectory across an occlusion if the deletion and accretion events are spatially displaced relative to the occluder edges (Experiment 1) or if deletion and accretion occur along a linear boundary that is incorrectly oriented relative to the occluder’s edges (Experiment 2). Thus congruence of these cues is apparently important for perception of veridical occlusion. These results are discussed in relation to an account of the development of perception of occlusion and object persistence.     

Infants' reasoning about opaque and transparent occluders in an individuation task

There has been some debate about whether infants 10 months and younger can use featural information to individuate objects. The present research tested the hypothesis that negative results obtained with younger infants reflect limitations in information processing capacities rather than the inability to individuate objects based on featural differences. Infants aged 9.5 months saw one object (i.e. a ball) or two objects (i.e. a box and a ball) emerge successively to opposite sides of an opaque occluder. Infants then saw a single ball either behind a transparent occluder or without an occluder. Only the infants who saw the ball behind the transparent occluder correctly judged that the one-ball display was inconsistent with the box-ball sequence. These results suggest that: (a) infants categorize events involving opaque and transparent occluders as the same kind of physical situation (i.e. occlusion) and (b) support the notion that infants are more likely to give evidence of object individuation when they need to reason about one kind of event (i.e. occlusion) than when they must retrieve and compare categorically distinct events (i.e. occlusion and no-occlusion).     

The role of three-dimensional depth cues in infants' perception of partly occluded objects

Newborn infants were familiarized to a three dimensional display consisting of a rod which moved behind a central occluder, so that only the top and bottom of the rod were visible. The infants' eyes were 38 cm from the rod and the occluder was 15 cm in front of the rod, a separation intended to ensure that the gap between the two was detected by the infants. On subsequent test trials the infants looked longer at a complete rod than at two rod pieces, suggesting that the hidden unity, or completeness of the rod had not been perceived. In a study by Johnson and Náñez (in press), using computer. generated stimuli, 4 month olds perceived the hidden unity of a similar display presented on a VDU in the complete absence of three. dimensional depth cues. Taken together, these findings suggest that, for these displays, perception of three. dimensional depth cues is not necessary for the detection of the unity of partially hidden objects. It is suggested that age changes in early infancy in the perception of occluded objects may result either from the emergence of abilities to perceive objects from kinematic information or from the emergence of sensitivity to that information itself.     

Luminance edges are not necessary for visual completion

Luminance edges seem to have an important role in visual feature binding and, more specifically, in visual completion because luminance differences are important for the perception of depth. We investigated this claim in two experiments in which the primed-matching paradigm was used. In Experiment 1, we investigated conditions under which either a partly occluded shape or an occluder was isoluminant with respect to the background. In Experiment 2, the partly occluded shape and the occluder were isoluminant with respect to each other. Evidence was found for visual completion in all cases, and we therefore conclude that luminance edges are not essential for visual completion.     

10‐month‐old infants’ inference of invisible agent: Distinction in causality between object motion and human action1

Abstract: Two habituation experiments investigated 10‐month‐old infants’ interpretation of events where a stationary object began to move without any visible causes. During habituation, infants saw that an object partly hidden by an occluder began to move away from the occluder. Then, they were tested with three test events without the occluder: the ?rst event showed a hand pushing the object, the second event showed a hand failing to touch the object, and the last event had no agent. The objects were a ball in Experiment 1, and a person in Experiment 2. The test event that the infants looked at for the shortest duration in Experiment 1 was where the hand pushed the ball, whereas they looked at the three test events almost equal amounts of time in Experiment 2. These results indicate that 10‐month‐old infants responded to the events in terms of causality and could infer the presence of the agent behind the occluder only when they saw the habituation event featuring the ball.     

Young infants' expectations about hidden objects

Infants aged 3-5 months (mean of approximately 4 months) were given a novel anticipatory looking task to test object permanence understanding. They were trained to expect an experimenter to retrieve an object from behind a transparent screen upon hearing a cue ("Doors up, here comes the hand"). The experimenter then hid the object behind one of two opaque screens and after either 2 or 8s gave the "doors up" cue. Infants looked to the correct location after the two-second delay, but not after the eight-second delay. This indicates a brief memory that the object is present behind the occluder. The study provides converging evidence that infants grasp object permanence by a young age. The novel anticipatory looking paradigm helps rule out counter-explanations applied to violation-of-expectation tasks.     

Illusory contour figures are perceived as occluding surfaces by 8‐month‐old infants

Infants have been demonstrated to be able to perceive illusory contours in Kanizsa figures. This study tested whether they also perceive these illusory figures as having the properties of real objects, such as depth and capability of occluding other objects. Eight‐ and five‐month‐old infants were presented with scenes that included a Kanizsa square and further depth cues provided by the deletion and accretion pattern of a moving duck. The 8‐month‐old infants looked significantly longer at the scene when the two types of occlusion cues were inconsistent than when they were consistent with each other, which provides evidence that they interpreted the Kanizsa square as a depth cue. In contrast, 5‐month‐olds did not show this difference. This finding demonstrates that 8‐month‐olds perceive the figure formed by the illusory contours as having properties of a real object that can act as an occluder.     

2.5-month-old infants' reasoning about when objects should and should not be occluded.

The present research examined 2.5-month-old infants' reasoning about occlusion events. Three experiments investigated infants' ability to predict whether an object should remain continuously hidden or become temporarily visible when passing behind an occluder with an opening in its midsection. In Experiment 1, the infants were habituated to a short toy mouse that moved back and forth behind a screen. Next, the infants saw two test events that were identical to the habituation event except that a portion of the screen's midsection was removed to create a large window. In one event (high-window event), the window extended from the screen's upper edge; the mouse was shorter than the bottom of the window and thus did not become visible when passing behind the screen. In the other event (low-window event), the window extended from the screen's lower edge; although the mouse was shorter than the top of the window and hence should have become fully visible when passing behind the screen, it never appeared in the window. The infants tended to look equally at the high- and low-window events, suggesting that they were not surprised when the mouse failed to appear in the low window. However, positive results were obtained in Experiment 2 when the low-window event was modified: a portion of the screen above the window was removed so that the left and right sections of the screen were no longer connected (two-screens event). The infants looked reliably longer at the two-screens than at the high-window event. Together, the results of Experiments 1 and 2 suggested that, at 2.5 months of age, infants possess only very limited expectations about when objects should and should not be occluded. Specifically, infants expect objects (1) to become visible when passing between occluders and (2) to remain hidden when passing behind occluders, irrespective of whether these have openings extending from their upper or lower edges. Experiment 3 provided support for this interpretation. The implications of these findings for models of the origins and development of infants' knowledge about occlusion events are discussed.     

Development of perceptual completion originates in information acquisition

Adults have little difficulty perceiving objects as complete despite occlusion, but newborn infants perceive moving partly occluded objects solely in terms of visible surfaces. The developmental mechanisms leading to perceptual completion have never been adequately explained. Here, the authors examine the potential contributions of oculomotor behavior and motion sensitivity to perceptual completion performance in individual infants. Young infants were presented with a center-occluded rod, moving back and forth against a textured background, to assess perceptual completion. Infants also participated in tasks to assess oculomotor scanning patterns and motion direction discrimination. Individual differences in perceptual completion performance were strongly correlated with scanning patterns but were unrelated to motion direction discrimination. The authors present a new model of development of perceptual completion that posits a critical role for targeted visual scanning, an early developing oculomotor action system.