When the ordinary seems unexpected: evidence for incremental physical knowledge in young infants

According to a recent account of infants' acquisition of their physical knowledge, the incremental-knowledge account, infants form distinct event categories, such as occlusion, containment, support, and collision events. In each category, infants identify one or more vectors which correspond to distinct problems that must be solved. For each vector, infants acquire a sequence of variables that enables them to predict outcomes within the vector more and more accurately over time. This account predicts that infants who have acquired only a few of the variables in a sequence should err in two ways in violation-of-expectation tasks: (1) they should view impossible events consistent with their incomplete knowledge as expected (errors of omission), and (2) they should view possible events inconsistent with their incomplete knowledge as unexpected (errors of commission). Many reports have shown that infants who have not yet identified a variable in an event category produce errors of omission: they fail to view impossible events involving the variable as unexpected. However, there has been no report revealing errors of commission in infants' responses to possible events. The present research examined whether 3- and 2.5-month-old infants, whose knowledge of occlusion events is very limited, would produce errors of commission as well as errors of omission when responding to these events. At 3 months of age, infants viewed as unexpected a possible event in which a tall cylinder became visible when passing behind a tall screen with a very large opening extending from its upper edge. At 2.5 months, infants viewed as unexpected a possible event in which a tall cylinder became visible when passing behind a tall screen with a very large opening extending from its lower edge. These findings provide a new kind of evidence for the incremental-knowledge account, and more generally for the notion that infants, like older children and adults, engage in rule-based reasoning about physical events.     

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.     

Using Language to Navigate the Infant Mind

ABSTRACT— How do infants represent objects, actions, and relations in events? In this review, we discuss an approach to studying this question that begins with linguistic theory—specifically, semantic structures in language. On the basis of recent research exploring infant cognition and prominent linguistic analyses, we examine whether infants' representations of motion events are articulated in terms of the components proposed by Talmy (1985 ; e.g., path, manner) and whether infants' event representations are defined in terms of broad semantic roles (agent, patient, source, goal) as proposed by Jackendoff (1990) and Dowty (1991) . We show how recent findings in infant cognition are consistent with the idea that the infant's representation of events is a close reflection of the linguistic categories. We especially highlight research that is explicitly guided by linguistic categories likely to have correlates in nonlinguistic cognition to illustrate the usefulness of using language to pose questions about early conceptual representations.     

Infants' physical knowledge affects their change detection

Prior research suggests that infants attend to a variable in an event category when they have identified it as relevant for predicting outcomes in the category, and that the age at which infants identify a variable depends largely on the age at which they are exposed to appropriate observations. Thus, depending on age of exposure, infants may identify the same variable at different ages in different event categories. A good case in point is the variable height, which is identified at about 3.5 months in occlusion events, but only at about 12 months in covering events and 14 months in tube events. In the present experiments, 11-month-olds detected a change to an object's height in an occlusion but not a covering event, and 12.5-month-olds detected a similar change in a covering but not a tube event. Thus, infants succeeded in detecting a change to an object's height in an event where height had been identified as a relevant variable, but failed to detect the exact same change in another event where height had not yet been identified as a relevant variable. These findings provide evidence that infants' physical knowledge affects which changes they detect in physical events. Possible mechanisms underlying these findings are also discussed, in light of recent accounts of change detection in adults.     

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' knowledge about occlusion and containment events: a surprising discrepancy

The present research examined whether infants acquire general principles or more specific rules when learning about physical events. Experiments 1 and 2 investigated 4.5-month-old infants' ability to judge how much of a tall object should be hidden when lowered behind an occluder versus inside a container. The results indicated that at this age infants are able to reason about height in occlusion but not containment events. Experiment 3 showed that this latter ability does not emerge until about 7.5 months of age. The marked discrepancy in infants' reasoning about height in occlusion and containment events suggests that infants sort events into distinct categories, and acquire separate rules for each category.     

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.     

Learning and discrimination of audiovisual events in human infants: the hierarchical relation between intersensory temporal synchrony and rhythmic pattern cues

This study examined 4- to 10-month-old infants' perception of audio-visual (A-V) temporal synchrony cues in the presence or absence of rhythmic pattern cues. Experiment 1 established that infants of all ages could successfully discriminate between two different audiovisual rhythmic events. Experiment 2 showed that only 10-month-old infants detected a desynchronization of the auditory and visual components of a rhythmical event. Experiment 3 showed that 4- to 8-month-old infants could detect A-V desynchronization but only when the audiovisual event was nonrhythmic. These results show that initially in development infants attend to the overall temporal structure of rhythmic audiovisual events but that later in development they become capable of perceiving the embedded intersensory temporal synchrony relations as well.     

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.     

Reasoning about containment events in very young infants

The present research examined very young infants' expectations about containment events. In Experiment 1, 3.5-month-old infants saw a test event in which an object was lowered inside a container with either a wide opening (open-container condition) or no opening (closed-container condition) in its top surface. The infants looked reliably longer at the closed- than at the open-container test event. These and baseline data suggested that the infants recognized that the object could be lowered inside the container with the open but not the closed top. In Experiment 2, 3.5-month-old infants saw a test event in which an object was lowered either behind (behind-container condition) or inside (inside-container condition) a container; next, the container was moved forward and to the side, revealing the object behind it. The infants looked reliably longer at the inside- than at the behind-container test event. These and baseline results suggested that the infants in the inside-container condition realized that the object could not pass through the back wall of the container and hence should have moved with it to its new location. Experiments 3 and 4 extended the results of Experiments 1 and 2 to 2.5-month-old infants. Together, the present results indicate that even very young infants possess expectations about containment events. The possible origins and development of these expectations are discussed in the context of Baillargeon's model (Advances in infancy research 9 (1995) 305. Norwood, NJ: Ablex) of infants' acquisition of physical knowledge, and of Spelke's proposal (Cognition 50 (1994) 431) that, from birth, infants interpret physical events in accord with a solidity principle.     

Developments in young infants' reasoning about occluded objects

Eight experiments were conducted to examine 3- and 3.5-month-old infants' responses to occlusion events. The results revealed two developments, one in infants' knowledge of when objects should and should not be occluded and the other in infants' ability to posit additional objects to make sense of events that would otherwise violate their occlusion knowledge. The first development is that, beginning at about 3 months of age, infants expect an object to become temporarily visible when passing behind an occluder with an opening extending from its lower edge. The second development is that, beginning at about 3.5 months of age, infants generate a two-object explanation when shown a violation in which an object fails to become visible when passing behind an occluder with an opening in its lower edge. Unless given information contradicting such an explanation, infants infer that two identical objects are involved in the event, one traveling to the left and one to the right of the opening. These and related findings provide the basis for a model of young infants' responses to occlusion events; alternative models are also discussed.     

Inducing infants to detect a physical violation in a single trial

There is increasing evidence that infants' representations of physical events can be enhanced through appropriate experiences in the laboratory. Most of this research has involved administering infants multiple training trials, often with multiple objects. In the present research, 8-month-olds were induced to detect a physical violation in a single trial. The experiments built on previous evidence that for occlusion events, infants encode height information at about age 3.5 months, but for covering events, they encode height information only at about age 12 months. In two experiments, a short cover was first placed in front of a short or a tall object (occlusion event); next, the cover was lowered over the tall object until it became fully hidden (covering event). Exposure to the occlusion event (but not other events in which height information was not encoded) enabled the infants to detect the violation in the covering event, much earlier than they would have otherwise.     

Visual experience enhances infants' use of task-relevant information in an action task

Four experiments examined whether infants' use of task-relevant information in an action task could be facilitated by visual experience in the laboratory. Twelve- but not 9-month-old infants spontaneously used height information and chose an appropriate (taller) cover in search of a hidden tall toy. After watching examples of covering events in a teaching session, 9-month-old infants succeeded in an action task that involved the same event category; learning was not generalized to events from a different category. The present results demonstrate that learning through visual experience can be transferred to infants' subsequent actions. These findings shed light on the link between perception and action in infancy.     

Perseverative responding in a violation-of-expectation task in 6.5-month-old infants

In the present research, 6.5-month-old infants perseverated in a violation-of-expectation task designed to examine their reasoning about width information in containment events. After watching a familiarization event in which a ball was lowered into a wide container, the infants failed to detect the violation in a test event in which the same ball was lowered into a container only half as wide as the ball (narrow-container test event). This negative result (which was replicated in another experiment) was interpreted in terms of a recent problem-solving account of infants' perseverative errors in various means-end tasks (Aguiar, A., & Baillargeon, R. (2000). Perseveration and problem solving in infancy. In H. W. Reese (Ed.), Advances in child development and behavior (Vol. 27, pp. 135-180). San Diego, CA: Academic Press). It was assumed that the infants in the present experiments (1) did not attend to the relative widths of the ball and container in their initial analysis of the narrow-container test event, (2) categorized the event as similar to the familiarization event shown on the preceding trials, and (3) retrieved the expectation they had formed for that event ("the ball will fit into the container"), resulting in a perseverative error. This interpretation was supported by additional experiments in which different modifications were introduced that led to non-perseverative responding, indicating that 6.5-month-old infants could detect the violation in the narrow-container test event. The present findings are important for several reasons. First, they provide the first demonstration of perseverative responding in a violation-of-expectation task. Second, they make clear the breadth and usefulness of the problem-solving account mentioned above. Finally, they add to the evidence for some degree of continuity between infants' and adults' problem-solving abilities.     

Evidence for task-dependent categorization in infancy

Two experiments compared infants' attention to the categorical distinction between people and animals in object-examining and sequential-touching tasks. In Experiment 1, 10- and 13-month-old infants distinguished between animals and people in an object-examining task. In this task, infants are familiarized with individual exemplars from one category, and then their response to exemplars from another category is measured. In Experiment 2, 13- and 16-month-old infants, but not 10-month-old infants, attended to the same distinction in a sequential-touching task. In this task, infants are presented with several exemplars from two categories simultaneously, and the order in which they touch those objects is assessed. Evaluation of infants' touching behavior in Experiment 2 also revealed developmental changes in how they approached this task. The combined results of these two experiments confirm the general trend reported in the literature and begin to provide insight into developmental changes that contribute to infants' ability to apply their categorization skills in different task contexts.     

Can 15-month-old infants understand pretence? An investigation using the 'violation-of-expectation' paradigm

Productive tests are unsuitable for measuring infants' earliest understanding of pretence, because performance demands may render infants unable to produce the actions required to pass the test. Recently, Onishi, Baillargeon and Leslie (2007) used the violation-of-expectation (VOE) paradigm as a measure of infants' understanding of others' pretence that is free from such performance demands. They found that 15-month-old infants looked longer at an Unexpected event in which an actor pretended to pour into one cup but pretended to drink from another cup, compared to pretending to pour and drink with the same cup. On this basis, they argued that 15-month-old infants expect others' pretence to be consistent, demonstrating their understanding of others' pretence. However, infants may have responded to expectations they had about familiar action sequences, rather than to pretence per se. To test this hypothesis, the current study firstly replicated Onishi et al.'s results in a sample of 28 typically developing 15-month-old infants, and then added a condition using closely matched real versions of their pretend VOE tasks. It was found that infants looked longer at unexpected events, whether or not the events were real or pretend. It was concluded that 15-month-old infants may look longer at pretend events due to violations of expectations they have about familiar action sequences, rather than because they understand others' pretence behaviour.     

When the event is more than the sum of its parts: 9-month-olds' long-term ordered recall

Research suggests that 9-month-old infants are able to recall single object-specific actions over delays of 24 hours. In the present research we investigated whether 9-month-olds are able to recall over more extended delays, and to recall the temporal order of events, as well as the individual actions in them. In addition, we investigated whether recall can be enhanced by pre- and/or re-exposure to target events. Using elicited imitation of novel, multi-step event sequences, we demonstrated that, as a group, 9-month-olds are able to recall target actions after delays of five weeks. However, after this long delay, only 45% of the infants recalled the temporal order of the events. Re-exposure to events during the delay interval proved necessary for boys, but not for girls; pre-exposure to events did not affect later recall. The implications of individual differences in infants' recall ability for the understanding of the development of the neural correlates of declarative memory are discussed.     

Experience matters: the impact of doing versus watching on infants' subsequent perception of tool-use events

Prior work suggests that active experience affects infants' understanding of simple actions. The present studies compared the impact of active and observational experience on infants' ability to identify the goal of a novel tool-use event. Infants either received active training and practice in using a cane to retrieve an out-of-reach toy or had matched observational experience before taking part in a habituation paradigm that we used to assess infants' ability to identify the goal of another person's tool-use acts. Active training alone facilitated 10-month-old infants' ability to identify the goal of the tool-use event. Active experience using tools may enable infants to build motor representations of tool-use events that subsequently guide action perception and support action understanding.     

The Development of Infants' Spatial Categories

ABSTRACT— Early theories of how infants develop spatial concepts focused on the perceptual and cognitive abilities that contribute to this ability. More recent research, however, has centered on whether experience with spatial language might also play a role. The present article reviews how infants learn to form spatial categories, outlining the perceptual and cognitive abilities that drive this learning, and examines the role played by spatial language. I argue that infants' spatial concepts initially are the result of nonlinguistic perceptual and cognitive abilities, but that, as infants build a spatial lexicon, spatial language becomes an important tool in the spatial categories infants learn to form.     

Scripts and checkerboards: The influence of ordered visual information on remembering locations in infancy

Five-month-old infants were trained to fixate 4 event locations, and memory for sequential locations was assessed following training. Results of two studies reveal that ordered visual information influences young infants' memory for sequential events.