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.     

A comparison of monocular and binocular depth perception in 5- and 7-month-old infants

Monocular depth perception was compared with binocular depth perception in 5- and 7-month-old infants. Reaching was used as the dependent measure. Two objects, identical except in size, were presented simultaneously to each infant. The smaller object was within reach for the infants while the larger object was just beyond reach. The two objects subtended equal visual angles from the infants' observation point. With binocular presentation, 96% of the 7-month-olds' reaches and 89% of the 5-month-olds' reaches were for the nearer object. With monocular presentation, 58% of the 7-month-olds' reaches and 65% of the 5-month-olds' reaches were for the nearer object. The reaching preferences observed in the monocular condition indicated sensitivity to monocular depth information (motion parallax, accommodation, and relative size information were available). Binocular viewing, however, resulted in a far more consistent tendency to reach for the nearer object. This result suggests that the infants' perception of the objects' distances was more veridical in the binocular condition than in the monocular condition.     

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.     

Intermodal perception of expressive behaviors by human infants

Four experiments demonstrate that infants of 5 and 7 months can detect information that is invariant across the acoustic and optic presentations of a single affective expression. Infants were presented simultaneously with two filmed facial expressions accompanied by a single vocal expression characteristic of one of the facial expressions. The infants increased their looking time to a facial expression when it was sound-specified, as compared to when that filmed expression was projected silently. Even when synchrony relations were disrupted, infants looked proportionately longer to the film that was sound-specified, indicating that some factor other than temporal synchrony guided the infants' looking behavior. When infants viewed the filmed facial expressions either in a normal orientation or upside-down, those infants viewing the facial expressions in the normal orientation looked appropriately, while those viewing the inverted films did not. These findings support the view that infants are sensitive to amodal, potentially meaningful invariant relations in expressive behaviors. These results are discussed in the context of J. J. Gibson's theory of affordances.     

Infant search strategies with containers that move but do not alter the location at which contents can be found

A number of hypotheses about infants' delayed search accuracy have been based upon the notion that a location associated with repeated retrieval of the object attains privileged status. Infants may need strong cues to search at a new location. However, a test is reported in which performance of 12- and 15-month-old infants was shown to be indifferent to the location. The results were reliable at an individual level. The data accord with previous research upon the canonicality effect in infant spatial search, an effect which is taken to index an experiential constraint on spatial discrimination. The experimental design thus serves as a discriminative test between three approaches: the original privileged location hypothesis, a newer spatial-contrast hypothesis, and a wider approach which focuses on experiential constraints on learning, including the canonicality effect.     

Learning of syllable-object relations by preverbal infants: The role of temporal synchrony and syllable distinctiveness

The role of temporal synchrony and syllable distinctiveness in preverbal infants’ learning of word-object relations was investigated. In Experiment 1, 7- and 8-month-olds (N = 64) were habituated under conditions where two similar-sounding syllables, /tah/ and /gah/, were spoken simultaneously with the motions of one of two sets of objects (synchronous) or out of phase with the motions (asynchronous). On test trials, 8-month-olds, but not 7-month-olds, showed learning of the relations in the synchronous condition but not in the asynchronous condition. Furthermore, in Experiment 2, following habituation to one of the synchronous syllable-object pairs, 7-month-olds (n = 8) discriminated the syllables and the objects. In Experiment 3, following habituation to two distinct syllables, /tah/-/gih/ or /gah/-/tih/, paired with identical objects, 7-month-olds (n = 40) showed learning of the relations, again only in the synchronous condition. Thus, synchrony, which mothers naturally provide between words and object motions, facilitated the mapping onto objects of similar-sounding syllables at 8 months of age and distinct syllables at 7 months of age. These findings suggest an interaction between infants’ synchrony and syllable distinctiveness perception during early word mapping development.     

Developmental changes in associations between auditory-visual events

The goal of the present study was twofold: to examine the influence of two amodal properties, co-location and temporal synchrony, on infants' associating a sight with a sound, and to determine if the relative influence of these properties on crossmodal learning changes with age. During familiarization 2-, 4-, 6- and 8-month-olds were presented two toys and a sound, with sights and sounds varying with respect to co-location and temporal synchrony. Following each familiarization phase infants were given a paired preference test to assess their learning of sight-sound associations. Measures of preferential looking revealed age-related changes in the influence of co-location and temporal synchrony on infants' learning sight-sound associations. At all ages, infants could use temporal synchrony and co-location as a basis for associating an auditory with a visual event and, in the absence of temporal synchrony, co-location was sufficient to support crossmodal learning. However, when these cues conflicted there were developmental changes in the influence of these cues on infants' learning auditory-visual associations. At 2 and 4 months infants associated the sounds with the toy that moved in synchrony with the sound's rhythm despite extreme violation of co-location of this sight and sound. In contrast, 6- and 8-month-olds did not associate a specific toy with the sound when co-location and synchrony information conflicted. The findings highlight the unique and interactive effects of distinct amodal properties on infants' learning arbitrary crossmodal relations. Possible explanations for the age shift in performance are discussed.     

Should all stationary objects move when hit? Developments in infants’ causal and statistical expectations about collision events

Four experiments examined 8- and 9-month-old infants’ expectations about collision events. The infants saw test events in which a small cylinder rolled down a ramp and hit one of several different boxes. These boxes varied in width and height and always remained stationary when hit. The results revealed two separate developments. The first involved infants’ knowledge of the variables relevant to collision events. At 8 months, the infants expected all of the boxes to move when hit, regardless of their sizes; at 9 months, the infants began to take into account the size of the boxes to predict whether they should move when hit. The second development concerned infants’ ability to generate explanations for outcomes that violated their collision knowledge. At both ages, upon observing that a box with a salient vertical dimension did not move when hit, the infants apparently concluded that the box must be one of those objects we term pillars—vertical objects that are attached at one or both ends to adjacent surfaces. At 8 months, the infants considered any vertical box as a potential pillar; at 9 months, the infants considered only boxes that were both vertical and narrow as potential pillars. The development of infants’ knowledge about collision events is thus one that is complex and protracted and weaves together many separate developments.     

Infants' intermodal perception of two levels of temporal structure in natural events

Infants' intermodal perception of two levels of temporal structure uniting the visual and acoustic stimulation from natural, complex events was investigated in four experiments. Films depicting a single object (single, large marble) and a compound object (group of smaller marbles) colliding against a surface in an erratic pattern were presented to infants between 3 and months of age using an intermodal preference and search method. These stimulus events portrayed two levels of invariant temporal structure: (a) temporal synchrony united the sights and sounds of object impact, and (b) temporal microstructure, the internal temporal structure of each impact sound and motion, specified the composition of the object (single vs. compound). Experiment 1 demonstrated that by 6 months infants detected a relation between the audible and visible stimulation from these events when both levels of invariant temporal structure guided their intermodal exploration. Experiment 2 revealed that by 6 months infants detected the bimodal temporal microstructure specifying object composition. They looked predominantly to the film whose natural soundtrack was played even though the motions of objects in both films were synchronized with the soundtrack. Experiment 3 assessed infants' sensitivity to temporal synchrony relations. Two films depicting objects of the same composition were presented while the motions of only one of them was synchronized with the appropriate soundtrack. Both 6-month-olds showed evidence of detecting temporal synchrony relations under some conditions. Experiment 4 examined how temporal synchrony and temporal microstructure interact in directing intermodal exploration. The natural soundtrack to one of the objects was played out-of-synchrony with the motions of both. In contrast with the results of Experiment 2, infants at 6 months showed no evidence of detecting a relationship between the film and its appropriate soundtrack. This suggests that the temporal asynchrony disrupted their detection of the temporal microstructure specifying object composition. Results of these studies support on invariant-detection view of the development of intermodal perception.     

Selective information use and perseveration in the search behavior of infants and young children

Two experiments examined the early development of selective information use in search. The first experiment tested 9- and 16-month-olds on a modification of Piaget's Stage IV object permanence task. It examined infants' use of information from previous experiences with an object (prior information) and from the most recent hiding (current information) to locate a hidden object. In the second experiment, 2-, $\text{2}\text{1}\text{2}$-, and 4-year-old children received these same sources of information along with new forms of prior and current information: information about the typical locations of objects (location specificity) and verbal information. No systematic perseveration was observed at 9 months, although previous findings related to perseveration were replicated. Perseveration was found at 16 months, but there was also evidence of selectivity at that age. When errors occurred, they tended to be to the prior location, but they were infrequent in comparison to correct searches at the current location. The preschoolers, while continuing to show perseveration, were more consistently selective than the infants. They also showed considerable generality in extending their selectivity to new sources of information.     

Effects of sound frequency on behavioral and cardiac orienting in newborn and five-month-old infants

Alert newborn and 5-month-old infants' responsivity to variations in spectral composition of a rattle sound was examined. Each child received four stimulus conditions: low-, mid-, and high-frequency bandpass-filtered rattles and an unfiltered broadband rattle. Stimuli were played through a single loudspeaker laterally positioned, and head orientation and cardiac responses to sound were recorded. Compared to other stimuli, the low-frequency sound elicted less head turning in both age groups, with this effect exaggerated in younger infants. Head orientation toward the mid-frequency, high-frequency, and broadband stimuli did not differ with age. For all conditions, latency and duration of newborns' head turning was longer than that of 5-month-olds. Newborns responded with cardiac deceleration only on trials when they failed to turn. When head turns occurred, an acceleratory cardiac response was obtained. Five-month-olds responded with reliable cardiac deceleration irrespective of head turning toward the sound. Heart rate change did not vary as a function of frequency at either age, suggesting that all stimuli were equally effective in eliciting the infant's attention.     

Factors influencing infants’ ability to update object representations in memory

Remembering persisting objects over occlusion is critical to representing a stable environment. Infants remember hidden objects at multiple locations and can update their representation of a hidden array when an object is added or subtracted. However, the factors influencing these updating abilities have received little systematic exploration. Here we examined the flexibility of infants’ ability to update object representations. We tested 11-month-olds in a looking-time task in which objects were added to or subtracted from two hidden arrays. Across five experiments, infants successfully updated their representations of hidden arrays when the updating occurred successively at one array before beginning at the other. But when updating required alternating between two arrays, infants failed. However, simply connecting the two arrays with a thin strip of foam-core led infants to succeed. Our results suggest that infants’ construal of an event strongly affects their ability to update memory representations of hidden objects. When construing an event as containing multiple updates to the same array, infants succeed, but when construing the event as requiring the revisiting and updating of previously attended arrays, infants fail.     

Rapid word learning in 13- and 17-month-olds in a naturalistic two-word procedure: looking versus reaching measures

This study investigated infants’ rapid learning of two novel words using a preferential looking measure compared with a preferential reaching measure. In Experiment 1, 21 13-month-olds and 20 17-month-olds were given 12 novel label exposures (6 per trial) for each of two novel objects. Next, in the label comprehension tests, infants were shown both objects and were asked, “Where’s the [label]?” (looking preference) and then told, “Put the [label] in the basket” (reaching preference). Only the 13-month-olds showed rapid word learning on the looking measure; neither age group showed rapid word learning on the reaching measure. In Experiment 2, the procedure was repeated 24 h later with 10 participants per age group from Experiment 1. After a further 12 labels per object, both age groups now showed robust evidence of rapid word learning, but again only on the looking measure. This is the earliest looking-based evidence of rapid word learning in infants in a well-controlled (i.e., two-word) procedure; our failure to replicate previous reports of rapid word learning in 13-month-olds with a preferential reaching measure may be due to our use of more rigorous controls for object preferences. The superior performance of the younger infants on the looking measure in Experiment 1 was not straightforwardly predicted by existing theoretical accounts of word learning.     

Infants' learning,memory, and generalization of learning for bimodal events

Study 1 investigated whether infants 3 and 7 months of age show differential learning of and memory for sight-sound pairs depending on whether or not temporal synchrony was present; memory was assessed after a 10-min and 1-week interval. Study 2 examined whether 7-month-olds show generalization of learning when they encounter novel bimodal events that are similar (changes in size, orientation, or color, and spectral sound properties) to the sight-sound pairs learned 1 week earlier based on temporal synchrony. For Study 1, infants received a familiarization phase followed by a paired-comparison preference procedure to assess for learning of the sight-sound pairs. One week later a memory test was given. Results confirmed that 7-month-olds had no difficulty learning auditory-visual pairings regardless of whether or not events were temporally synchronous, and they remembered these 10 min and 1 week later. In contrast, 3-month-olds showed poorer learning of sight-sound associations in the no-synchrony than synchrony conditions, and memory for sight-sound pairs 1 week later was shown only for the synchrony conditions. Results for Study 2 revealed generalization of learning of bimodal pairings under all stimulus conditions after a 1-week interval at 7 months of age. Implications of these findings for development of intersensory knowledge are discussed.     

Infants’ responses to objects representing levels of word knowledge and categorical information

The effects of differing levels of word knowledge on infants’ sequential touching behaviors were investigated in two studies. In both, parent report was used to assess three levels of word knowledge: known, frontier, and unknown. In the first study, 14-month-old infants sequentially touched objects consistent with parents’ reports of their word knowledge. In the second study, 20-month-old infants sequentially touched objects by both conceptual category and reported level of word knowledge. It appears that even infants, like adults, can make distinctions among objects on the basis of their knowledge about the objects’ labels.     

Learning to form relationships in infancy: Parallel attainments with parents and peers

Freud's assertion notwithstanding, the attachment relationship is not “without parallel” in social life. Children's attainments in forming attachments to parents parallel the steps they take in relating to their peers. During the first 3 years of life, in both domains, infants come to recognize prospective social partners, communicate with them, engage them in patterned interaction, including both cooperation and conflict, learn from their presence and actions, and interact in idiosyncratic ways with particular companions. Toward the end of this period, children show signs of acquiring generalized concepts of the social relationships in which they engage. It is proposed that biological constraints on learning promote human infants' interest in and rudimentary abilities to interact with other members of their species. Subsequent incidental and intentional learning processes shape both the child's attachments and less intense relationships with other persons.     

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.     

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.     

Object individuation and labelling in 6-month-old infants

The ability to determine how many objects are involved in physical events is fundamental for reasoning about the world that surrounds us. Previous studies suggest that infants can fail to individuate objects in ambiguous occlusion events until their first birthday and that learning words for the objects may play a crucial role in the development of this ability. The present eye-tracking study tested whether the classical object individuation experiments underestimate young infants’ ability to individuate objects and the role word learning plays in this process. Three groups of 6-month-old infants (N = 72) saw two opaque boxes side by side on the eye-tracker screen so that the content of the boxes was not visible. During a familiarization phase, two visually identical objects emerged sequentially from one box and two visually different objects from the other box. For one group of infants the familiarization was silent (Visual Only condition). For a second group of infants the objects were accompanied with nonsense words so that objects’ shape and linguistic labels indicated the same number of objects in the two boxes (Visual & Language condition). For the third group of infants, objects’ shape and linguistic labels were in conflict (Visual vs. Language condition). Following the familiarization, it was revealed that both boxes contained the same number of objects (e.g. one or two). In the Visual Only condition, infants looked longer to the box with incorrect number of objects at test, showing that they could individuate objects using visual cues alone. In the Visual & Language condition infants showed the same looking pattern. However, in the Visual vs Language condition infants looked longer to the box with incorrect number of objects according to linguistic labels. The results show that infants can individuate objects in a complex object individuation paradigm considerably earlier than previously thought and that linguistic cues enforce their own preference in object individuation. The results are consistent with the idea that when language and visual information are in conflict, language can exert an influence on how young infants reason about the visual world.     

Increasing specificity in perceptual development: infants' detection of nested levels of multimodal stimulation

This research assessed the development of infants' sensitivity to two nested amodal temporal relations in audible and visible events. Their detection of global temporal synchrony between visible and audible impacts and internal temporal structure nested within each impact specifying object composition (single versus compound objects) was assessed. Infants of 4, 7, and 11 weeks of age were habituated to a single and a compound object striking a surface and then received test trials depicting a change in synchrony or object composition. Results indicated an interaction between age and condition where sensitivity to synchrony was present by 4 weeks and remained stable across age, whereas sensitivity to composition emerged later, by 7 weeks, and increased dramatically with age. These findings converge with other recent findings to illustrate a pattern of increasing specificity in the development of perception, where infants first detect global and later detect embedded relations. The early sensitivity to global relations may provide an organizational framework for development by focusing infant attention on unitary events, guiding and constraining further exploration, and buffering infants from learning incongruent relations.