Reasoning about a hidden object after a delay: evidence for robust representations in 5-month-old infants

The present research examined two alternative interpretations of violation-of-expectation findings that young infants can represent hidden objects. One interpretation is that, when watching an event in which an object becomes hidden behind another object, infants form a prediction about the event's outcome while both objects are still visible, and then check whether this prediction was accurate. The other interpretation is that infants' initial representations of hidden objects are weak and short-lived and as such sufficient for success in most violation-of-expectation tasks (as objects are typically hidden for only a few seconds at a time), but not more challenging tasks. Five-month-old infants succeeded in reasoning about the interaction of a visible and a hidden object even though (1) the two objects were never simultaneously visible, and (2) a 3- or 4-min delay preceded the test trials. These results provide evidence for robust representations of hidden objects in young infants.     

Categorization of two-dimensional and three-dimensional stimuli by 18-month-old infants

In two experiments, 18-month-old infants’ categorization of 3D replicas and 2D photographs of the same animals and vehicles were compared to explore infants’ flexibility in categorization across different object representations. Using a sequential touching procedure, infants completed one superordinate and two basic-level categorization tasks with 3D replicas, 2D cut out photographs, or 2D images on photo cubes (“2D cubes”). For superordinate sets, 3D replicas elicited longer mean run lengths than 2D cut outs, and 3D replicas elicited equivalent mean run lengths as 2D cubes. For basic-level sets, infants categorized high-contrast animal sets when presented with 3D replicas, but they failed to categorize any of the 2D photograph sets. Categorization processes appear to differ for 3D and 2D stimuli, and infants’ discovery of object properties over time while manipulating objects may facilitate categorization, as least at the superordinate level. These findings are discussed in the context of infants’ representation abilities and the integration of perception and action.     

Factors affecting infants' manual search for occluded objects and the genesis of object permanence

Two experiments systematically examined factors that influence infants’ manual search for hidden objects (N = 96). Experiment 1 used a new procedure to assess infants’ search for partially versus totally occluded objects. Results showed that 8.75-month-old infants solved partial occlusions by removing the occluder and uncovering the object, but these same infants failed to use this skill on total occlusions. Experiment 2 used sound-producing objects to provide a perceptual clue to the objects’ hidden location. Sound clues significantly increased the success rate on total occlusions for 10-month-olds, but not for 8.75-month-olds. An identity development account is offered for why infants succeed on partial occlusions earlier than total occlusions and why sound helps only the older infants. We propose a mechanism for how infants use object identity as a basis for developing a notion of permanence. Implications are drawn for understanding the dissociation between looking time and search assessments of object permanence.     

Color-function categories that prime infants to use color information in an object individuation task

There is evidence for developmental hierarchies in the type of information to which infants attend when reasoning about objects. Investigators have questioned the origin of these hierarchies and how infants come to identify new sources of information when reasoning about objects. The goal of the present experiments was to shed light on this debate by identifying conditions under which infants’ sensitivity to color information, which is slow to emerge, could be enhanced in an object individuation task. The outcome of Experiment 1 confirmed and extended previous reports that 9.5-month-olds can be primed, through exposure to events in which the color of an object predicts its function, to attend to color differences in a subsequent individuation task. The outcomes of Experiments 2-4 revealed age-related changes in the nature of the representations that support color priming. This is exemplified by three main findings. First, the representations that are formed during the color-function events are relatively specific. That is, infants are primed to use the color difference seen in the color-function events to individuate objects in the test events, but not other color differences. Second, 9.5-month-olds can be led to form more abstract event representations, and then generalize to other colors in the test events if they are shown multiple pairs of colors in the color-function events. Third, slightly younger 9-month-olds also can be led to form more inclusive categories with multiple color pairs, but only when they are allowed to directly compare the exemplars in each color pair during the present events. These results shed light on the development of categorization abilities, cognitive mechanisms that support color-function priming, and the kinds of experiences that can increase infants’ sensitivity to color information.     

Common ground on object use associates with caregivers’ gesturese

Caregivers modify their communication when interacting with infants, and these modifications have been related to children's language development. However, the factors influencing caregivers’ modification of gestures are understudied. This study examined whether infants’ object knowledge, considered as common ground shared with the caregiver, relates to caregivers’ gesturese. Six caregiver-infant dyads were videotaped every two months for 15 min in their homes, from child age 8-to-16 months, while they played with two separate objects (i.e. toys). Results indicated that the changes in infants’ object knowledge were paralleled by associated changes in caregivers’ gestures: parents increased both the amount and the complexity of their gestures.     

Predicting sights from sounds: 6-month-olds' intermodal numerical abilities

Although the psychophysics of infants’ nonsymbolic number representations have been well studied, less is known about other characteristics of the approximate number system (ANS) in young children. Here three experiments explored the extent to which the ANS yields abstract representations by testing infants’ ability to transfer approximate number representations across sensory modalities. These experiments showed that 6-month-olds matched the approximate number of sounds they heard to the approximate number of sights they saw, looking longer at visual arrays that numerically mismatched a previously heard auditory sequence. This looking preference was observed when sights and sounds mismatched by 1:3 and 1:2 ratios but not by a 2:3 ratio. These findings suggest that infants can compare numerical information obtained in different modalities using representations stored in memory. Furthermore, the acuity of 6-month-olds’ comparisons of intermodal numerical sequences appears to parallel that of their comparisons of unimodal sequences.     

Something old,something new: a developmental transition from familiarity to novelty preferences with hidden objects

Novelty seeking is viewed as adaptive, and novelty preferences in infancy predict cognitive performance into adulthood. Yet 7‐month‐olds prefer familiar stimuli to novel ones when searching for hidden objects, in contrast to their strong novelty preferences with visible objects ( Shinskey & Munakata, 2005 ). According to a graded representations perspective on object knowledge, infants gradually develop stronger object representations through experience, such that representations of familiar objects can be better maintained, supporting greater search than with novel objects. Object representations should strengthen with further development to allow older infants to shift from familiarity to novelty preferences with hidden objects. The current study tested this prediction by presenting 24 11‐month‐olds with novel and familiar objects that were sometimes visible and sometimes hidden. Unlike 7‐month‐olds, 11‐month‐olds showed novelty preferences with both visible and hidden objects. This developmental shift from familiarity to novelty preference with hidden objects parallels one that infants show months earlier with perceptible stimuli, but the two transitions may reflect different underlying mechanisms. The current findings suggest both change and continuity in the adaptive development of object representations and associated cognitive processes.     

Twenty four-month-old infants’ interpretations of novel verbs and nouns in dynamic scenes

The current experiments address several concerns, both empirical and theoretical in nature, that have surfaced within the verb learning literature. They begin to reconcile what, until now, has been a large and largely unexplained gap between infants’ well-documented ability to acquire verbs in the natural course of their lives and their rather surprising failures to do so in many laboratory-based tasks. We presented 24-month-old infants with dynamic scenes (e.g., a man waving a balloon), and asked (a) whether infants could construe these scenes flexibly, noticing the consistent action (e.g., waving) as well as the consistent object (e.g., the balloon) and (b) whether their construals of the scenes were influenced by the grammatical form of a novel word used to describe them (verb or noun). We document that 24-month-olds’ representations of novel words are sufficiently precise to permit them to map novel verbs to event categories (e.g., waving events) and novel nouns to object categories (e.g., balloons). We also document the time-course underlying infants’ mapping of the novel words. These results beckon us to move beyond asking whether or not infants can represent verb meanings, and to consider instead the conditions that support successful verb learning in infants and young children.     

The effect of spatial cues on infants’ responses in the AB task,with and without a hidden object

The errors made by infants in the AB task were taken by Piaget as an indication of an inability to update their representations of the spatial location of a hidden object. This paper presents an experiment designed to further investigate the role of spatial representations in the production of the error. The introduction of strong visual cues to spatial location was found to reduce the traditional A‐not‐B search error. However, it also increased perseveration when a ‘lids‐only’ analogue of the AB task was used, in which infants are simply cued to pick up lids rather than encouraged to search for a hidden object. These results present a challenge to the dynamic systems account of the error given by Smith, Thelen, Titzer and McLin (Psychological Review, 106 (1999), 235–260), and indicate that the traditional A‐not‐B search error arises from a difficulty in updating representations of the spatial location of hidden objects. The relation of these results to Munakata’s PDP model (Developmental Science, 1 (1998), 161–211) and Thelen, Schöner, Scheier and Smith’s (Behavioural and Brain Sciences, 24 (2001), 1‐‐86) most recent dynamic systems model of the A‐not‐B error is also discussed.     

Toddlers’ cognition of adding and subtracting objects in action and in perception

A first experiment tested infants’ perceptual discrimination between correct and incorrect adding and subtracting objects with a standardized violation-of-expectation procedure. Eleven-, 16- and 21-month-olds did not look longer at incorrect (one object) than at correct (two objects) results of adding one object to another, nor at incorrect (two objects) than at correct (one object) results of subtracting one object from two. A second experiment tested 21-month-olds’ sensorimotor production of addition and subtraction results using a search-for-objects procedure. They already searched correctly for two objects when one object is added to another and for one object when one is subtracted from two objects. These findings support the constructivist hypothesis that infants’ active sensorimotor production may develop before their reactive perceptual discrimination of adding and subtracting objects.     

The sound of darkness: why do auditory cues aid infants' search for objects hidden by darkness but not by visible occluders?

In manual search tasks designed to assess infants' knowledge of the object concept, why does search for objects hidden by darkness precede search for objects hidden by visible occluders by several months? A graded representations account explains this décalage by proposing that the conflicting visual input from occluders directly competes with object representations, whereas darkness merely weakens representations. This study tests the prediction that representations of objects hidden by darkness are strong enough for infants to bind auditory cues to them and support search, whereas representations of objects hidden by occluders are not. Six-and-half-month-olds were presented with audible or silent objects that remained visible, became hidden by darkness, or became hidden by a visible occluder. Search required engaging in the same means-end action in all conditions. As predicted, auditory cues increased search when objects were hidden by darkness but not when they were hidden by a visible occluder. Results are discussed in the context of different facets of object concept development highlighted by graded representations perspectives and core knowledge perspectives and in relation to other work on multimodal object representations.     

The infant's acquisition of knowledge of bimodally specified events

Four-month-old infants viewed, for a duration of several minutes, two objects that bounced in synchrony with two percussion sounds. This synchrony was the only information tying each sound to its respective object. During the viewing the infants learned about the relationships between sound and object. Learning was revealed in two ways. In a search test, infants looked for an object when its sound was played. In a transfer test, infants' declining interest in a sound presented alone generalized to the visible object that the sound specified. Studies that reversed the spatial locations of the objects revealed that sound-object learning, rather than place or response learning, guided infants' perceptual exploration.     

Objects are individuals but stuff doesn't count: perceived rigidity and cohesiveness influence infants' representations of small groups of discrete entities

Young infants construct models of the world composed of objects tracked through time and occlusion. To date little is known about the degree to which these models are sensitive to the material make-up of the represented individuals. Two experiments probed 8-month-olds' ability to represent different kinds of entities: rigid, cohesive objects, flexible, cohesive objects, and non-rigid, non-cohesive portions of sand. In Experiment 1, infants represented an array of two rigid, cohesive objects hidden behind a single screen, but failed to represent hidden arrays of two flexible objects or two portions of sand. In Experiment 2, entities were hidden behind two screens instead of one, thereby reducing the information processing demands of the task. In that case, infants succeeded in representing arrays of both types of object stimuli, but again failed to represent the portions of sand. It is argued that (1) the processes by which infants individuate and track entities are sensitive to material kind, (2) rigid cohesive objects occupy a privileged status in this system, and (3) early knowledge about objects and substances has a quantificational aspect.     

Spatial updating according to a fixed reference direction of a briefly viewed layout

Three experiments examined the role of reference directions in spatial updating. Participants briefly viewed an array of five objects. A non-egocentric reference direction was primed by placing a stick under two objects in the array at the time of learning. After a short interval, participants detected which object had been moved at a novel view that was caused by table rotation or by their own locomotion. The stick was removed at test. The results showed that detection of position change was better when an object not on the stick was moved than when an object on the stick was moved. Furthermore change detection was better in the observer locomotion condition than in the table rotation condition only when an object on the stick was moved but not when an object not on the stick was moved. These results indicated that when the reference direction was not accurately indicated in the test scene, detection of position change was impaired but this impairment was less in the observer locomotion condition. These results suggest that people not only represent objects’ locations with respect to a fixed reference direction but also represent and update their orientation according to the same reference direction, which can be used to recover the accurate reference direction and facilitate detection of position change when no accurate reference direction is presented in the test scene.     

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.     

How 7-month-olds interpret ambiguous motion events: Category-based reasoning in infancy

This paper investigates the role of static and dynamic attributes for the animate-inanimate distinction in category-based reasoning of 7-month-olds. Three experiments tested infants’ responses to movement events involving an unfamiliar animal and a ball. When either the animal or the ball showed self-initiated irregular movements (Experiment 1), infants expected the previously active object to start moving again. When both objects were moving together in an ambiguous motion event (Experiment 2), infants expected only the animal to start moving again. Initial looking preferences for each object did not influence results. When either the facial features of the animal were removed, or its furry body was replaced by a plastic spiral in an ambiguous motion event (Experiment 3), infants formed no clear expectation regarding future movements. Based on this set of findings we conclude that 7-month-olds flexibly combine information about the static and dynamic properties of objects in order to reason about motion events.     

A double-dissociation in infants' representations of object arrays

Previous studies show that infants can compute either the total continuous extent (e.g. Clearfield, M.W., & Mix, K.S. (1999). Number versus contour length in infants' discrimination of small visual sets. Psychological Science, 10(5), 408-411; Feigenson, L., & Carey, S. (2003). Tracking individuals via object-files: evidence from infants' manual search. Developmental Science, 6, 568-584) or the numerosity (Feigenson, L., & Carey, S. (2003). Tracking individuals via object-files: evidence from infants' manual search. Developmental Science, 6, 568-584) of small object arrays. The present experiments asked whether infants can compute both extent and number over a given array. Experiment 1 used a habituation procedure to show that 7-month-old infants can compute numerosity when the objects in the array contrast in color, pattern, and texture. Experiment 2 revealed that, with these heterogeneous arrays, infants no longer represent the array's total continuous extent. Since previous work shows that infants compute continuous extent but not numerosity when objects have identical rather than contrasting properties, these results form a double dissociation. Infants computed number but not extent over representations of contrasting objects, and computed extent but not number over representations of identical objects.     

Infants recognize similar goals across dissimilar actions involving object manipulation

We investigated infants’ ability to recognize the similarity between observed and implied goals when actions differed in surface-level motion details. In two experiments, 10- to 12-month-olds were habituated to an actor manipulating an object and then shown test actions in which the actor contacted the object with a novel hand configuration that implied a goal either similar or dissimilar to the habituation event. Infants in both experiments looked significantly longer at test actions depicting a novel implied goal, suggesting that infants glossed over some surface-level motion details and compared implied goals.     

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.     

Sensitivity to binocular depth information in infants

In order to study infants' sensitivity to binocular information for depth, 11 infants, 20 to 26 weeks of age, were presented with real and stereoscopically projected virtual objects at three distances, and the infants' reaching behavior was videotaped. When the virtual object was positioned out of reach, infants tended to lean further forward and to reach less frequently than when the virtual object was positioned within reach. In addition, the proportion of reaches in which the infants patted, closed their hands, or brought their hands together was greater when the virtual object was within reach. However, no difference in the terminal location of the infants' reaches was found as a function of the virtual object's position. Examination of reaches to a near real object revealed that infants frequently did not contact the object or show appropriate hand shape or orientation. The effectiveness of the cue of retinal size and of binocular information for the depth of an object is discussed. It is concluded that 5-month-old infants are sensitive to binocular information for depth.