Infants' knowledge of objects: beyond object files and object tracking

Two independent research communities have produced large bodies of data concerning object representations: the community concerned with the infant's object concept and the community concerned with adult object-based attention. We marshal evidence in support of the hypothesis that both communities have been studying the same natural kind. The discovery that the object representations of young infants are the same as the object files of mid-level visual cognition has implications for both fields.     

Infants' individuation of agents and inert objects

Using the violation-of-expectancy method, we investigated 10-month-old infants' ability to rely on dynamic features in object individuation processes. Infants were first familiarized to events in which two different objects repeatedly appeared and disappeared, one at a time from behind a screen; at test, the screen was removed, revealing either one or two objects. In Experiment 1, one self-moving non-rigid agent and one inert object were involved in each trial, while in Experiment 2 two different agents were presented. Infants preferred to look at one-object outcomes in Experiment 1, but they did not show any preference for one- or two-object outcomes in Experiment 2. The results suggest that infants can use dynamic information to detect agents in complex individuation tasks before they can rely on shape or surface features. We propose that the sortals agent and inert object appear in development before 12 months without a substantial contribution of linguistic experience. These findings may motivate a revision of current theories on the development of kind-based individuation and object files.     

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.     

Infants' formation and use of categories to segregate objects

Four- and-a-half-month-old infants' (N = 100) category formation and use was studied in a series of five experiments. For each experiment, the test events featured a display composed of a cylinder and a box. Previous research showed that this display is not clearly parsed as a single unit or as two separate units by infants of this age. Immediately prior to testing, infants were shown a set of category exemplars. Knowledge about this category could help infants disambiguate the test display, which contained a novel exemplar of this category. Clear interpretation of the test display as composed of two separate units (as indicated by infants' longer looking at the move-together than at the move-apart test event) was taken as evidence of category formation and use. In Experiments 1 and 5, infants' prior experience with a set of three different boxes that were similar to the test box facilitated their segregation of the test display. Experiment 2 showed that three different exemplars are necessary: prior experience with any two of the three boxes used in Experiment 1 did not facilitate infants' segregation of the test display. Experiment 3 showed that variability in the exemplar set is necessary: prior experience with three identical boxes did not facilitate infants' segregation of the test display. Experiment 4 showed that under these conditions of very brief prior exposure, similarity between the exemplar set and test box is necessary: prior experience with three different boxes that were not very similar to the test box did not facilitate infants' segregation of the test display. Together, these findings suggest that: (a) number of exemplars, variability, and similarity in the exemplar set are important for infants' category formation, and (b) infants use their category knowledge to determine the boundaries of the objects in a display.     

Infants' responsiveness to line junctions in curved objects

Several empirical studies demonstrate that infants under 6-7 months of age are unable to extract static-monocular depth information from their environment. The aim of this study was to extend these findings by using a three-dimensional structure indicated by curved Y junctions. Infants 5 and 8 months of age were habituated to the line drawing of a cylinder. During test trials, the infants viewed two displays, one in which a surface marking had been deleted from the habituation figure and one in which an edge had been erased. An ANOVA revealed that the 8-month-old subjects looked significantly longer at the dishabituation display lacking the edge, whereas the 5-month-olds did not. The results provide evidence that 8-month-old infants distinguish between lines indicating edges and lines indicating markings and that they are able to use line junctions to perceive line drawings as depictions of three-dimensional objects in the picture plane.     

Infants' ability to use luminance information to individuate objects

Recent research indicates that infants first use form and then surface features as the basis for individuating objects. However, very little is known about the underlying basis for infants' differential sensitivity to form than surface features. The present research assessed infants' sensitivity to luminance differences. Like other surface properties, luminance information typically reveals little about an object. Unlike other surface properties (e.g. pattern, color), the visual system can detect luminance differences at birth. The outcome of two experiments indicated that 11.5-month-olds, but not 7.5-month-olds, used luminance differences to individuate objects. These results suggest that it is not the age at which infants can detect a feature, but the nature of the information carried by the feature, that determines infants' capacity to individuate objects.     

Infants' comprehension of toy replicas as symbols for real objects

Infants' understanding of toy model-real exemplar relations was assessed through preferential looking and habituation tasks. Results from the preferential looking task suggest that 18-month toddlers are just beginning to demonstrate comprehension of symbolic relations between iconic models and their real object counterparts. Performance of 10- and 14-month-old infants in the preferential looking task did not improve when across-domain pairs of videos were used in place of within-domain pairs. Habituation task results indicated that 10-month-olds do not comprehend symbolic relations between miniature toy replicas and their "real" counterparts, but that such understanding begins to emerge by age 14 months. Interactions between symbolic processing and early lexical development are considered, as are methodological implications for the study of infant categorization.     

Attentive tracking of objects versus substances

Recent research in vision science, infant cognition, and word learning suggests a special role for the processing of discrete objects. But what counts as an object? Answers to this question often depend on contrasting object-based processing with the processing of spatial areas or unbound visual features. In infant cognition and word learning, though, another salient contrast has been between rigid cohesive objects and nonsolid substances. Whereas objects may move from one location to another, a nonsolid substance must pour from one location to another. In the study reported here, we explored whether attentive tracking processes are sensitive to dynamic information of this type. Using a multiple-object tracking task, we found that subjects could easily track four items in a display of eight identical unpredictably moving entities that moved as discrete objects from one location to another, but could not track similar entities that noncohesively "poured" from one location to another-even when the items in both conditions followed the same trajectories at the same speeds. Other conditions revealed that this inability to track multiple "substances" stemmed not from violations of rigidity or cohesiveness per se, because subjects were able to track multiple noncohesive collections and multiple nonrigid deforming objects. Rather, the impairment was due to the dynamic extension and contraction during the substancelike motion, which rendered the location of the entity ambiguous. These results demonstrate a convergence between processes of midlevel adult vision and infant cognition, and in general help to clarify what can count as a persisting dynamic object of attention.     

Infants' categorization of novel objects with more or less obvious features

In five experiments, 14- to 15-month-old infants' categorization of objects on the basis of more or less obvious features was investigated. Using an object examining paradigm, a total of 200 infants were familiarized with novel objects that shared either more obvious features (i.e., easily visible) or less obvious features (i.e., accessible by lifting a flap), followed by an in-category object and an out-of-category object. When only perceptual information was available, infants formed a category on the basis of the more obvious features but not on the basis of the less obvious features (Experiments 1 and 3). When infants were provided with animacy cues and/or object names, they formed categories on the basis of either more or less obvious features (Experiments 2, 4, and 5). The results of these studies delineate the role of animacy cues and object names in establishing categories on the basis of less obvious features.     

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' search for visible objects: implications for the interpretation of early search errors

This study examined the error patterns of 9-month-old infants searching for hidden objects and objects that were visible within a container. Although errors occurred in both conditions, there were important differences between them. When the object was hidden, infants showed significant perseveration in that they searched more often at the object's previous hiding place than at a control location. When the object was visible, however, they made fewer errors and the errors they did make were as likely to be to the control location as to the previous hiding place. These results suggest that infants' errors in searching for a visible object reflect lapses of attention rather than systematic misunderstandings of objects or space and so are not incompatible with an information-processing account of early search.     

Infants' use of category knowledge and object attributes when segregating objects at 8.5 months of age

The current research investigates infants' perception of a novel object from a category that is familiar to young infants: key rings. We ask whether experiences obtained outside the lab would allow young infants to parse the visible portions of a partly occluded key ring display into one single unit, presumably as a result of having categorized it as a key ring. This categorization was marked by infants' perception of the keys and ring as a single unit that should move together, despite their attribute differences. We showed infants a novel key ring display in which the keys and ring moved together as one rigid unit (Move-together event) or the ring moved but the keys remained stationary throughout the event (Move-apart event). Our results showed that 8.5-month-old infants perceived the keys and ring as connected despite their attribute differences, and that their perception of object unity was eliminated as the distinctive attributes of the key ring were removed. When all of the distinctive attributes of the key ring were removed, the 8.5-month-old infants perceived the display as two separate units, which is how younger infants (7-month-old) perceived the key ring display with all its distinctive attributes unaltered. These results suggest that on the basis of extensive experience with an object category, infants come to identify novel members of that category and expect them to possess the attributes typical of that category.     

Age-related changes in attentional tracking of multiple moving objects

In a multiple-object tracking (MOT) task, young and older adults attentively tracked a subset of 10 identical, randomly moving disks for several seconds, and then tried to identify those disks that had comprised the subset. Young adults who habitually played video games performed significantly better than those who did not. Compared to young subjects (mean age = 20.6 years) with whom they were matched for video game experience, older subjects (mean age = 75.3 years) showed much reduced ability to track multiple moving objects, particularly with faster movement or longer tracking times. Control measurements with stationary disks show that the age-related decline in MOT was not caused by a general change in memory per se. To generate an item-wise performance measure, we examined older subjects' proportion correct according to the serial order in which individual disks were identified. Correct identification of target disks declined with the order in which targets were reported, suggesting that attentional tracking produced graded, rather than all-or-none, outcomes.     

A simple proximity heuristic allows tracking of multiple objects through occlusion

Moving objects in the world present a challenge to the visual system, in that they often move in and out of view as they are occluded by other surfaces. Nevertheless, the ability to track multiple objects through periods of occlusion is surprisingly robust. Here, we identify a simple heuristic that underlies this ability: Pre- and postocclusion views of objects are linked together solely by their spatial proximity. Tracking through occlusion was always improved when the postocclusion instances reappeared closer to the preocclusion views. Strikingly, this was true even when objects?? previous trajectories predicted different reappearance locations and when objects reappeared ??too close,?? from invisible ??slits?? in empty space, rather than from more distant occluder contours. Tracking through occlusion appears to rely only on spatial proximity, and not on encoding heading information, likely reappearance locations, or the visible structure of occluders.     

The role of location and motion information in the tracking and recovery of moving objects

Observers in a multiple object tracking task can track about four to five independently moving targets among several moving distractors, even if all of the stimuli disappear for a 300-msec gap. How observers reacquire targets following such a gap reveals what kind of information they can maintain for targets. Previous research has suggested that participants maintain minimal information about a set of moving objects--namely, just their present spatial locations. We report five new experiments that demonstrate retention of location information for at least four objects, and extrapolated motion information for around two objects.     

Infants' Physical World

Abstract— Investigations of infants' physical world over the past 20 years have revealed two main findings. First, even very young infants possess expectations about physical events. Second, these expectations undergo significant developments during the first year of life, as infants form event categories, such as occlusion, containment, and covering events, and identify the variables relevant for predicting outcomes in each category. A new account of infants' physical reasoning integrates these findings. Predictions from the account are examined in change-blindness and teaching experiments.     

Infants' perception of transparency

Four- and 7-month-old infants' perception of transparency was investigated with computer-generated achromatic or color displays depicting a semitransparent box occluding the center of a rod. Following habituation, infants viewed test displays consisting of either a two-color rod (corresponding to the habituation display's proximal characteristics) or a solid rod (corresponding to the distal characteristics of the event depicted by the habituation display). Looking-time results from 4-month-olds suggested perception of transparency in color displays but not in an achromatic display. An additional condition indicated that transparency perception may rely on the visibility of background texture through the transparent surface. Seven-month-olds, in contrast, provided some evidence of transparency perception in the achromatic display. Implications for the development of infants' responses to object properties and perceptual segregation are discussed.