Infants' Sensitivity to the Causal Features of Means‐End Support Sequences in Action and Perception

Current work has yielded differential findings regarding infants' ability to perceptually detect the causal structure of a means‐end support sequence. Resolving this debate has important implications for perception‐action dissociations in this domain of object knowledge. In Study 1, 12‐month‐old infants' ability to perceive the causal structure of a cloth‐pulling sequence was assessed via a habituation paradigm. After seeing an event in which a supported toy was moved by pulling a cloth that it sat on, 12‐month‐old infants demonstrated longer looking to events that violated the causal structure of this sequence than to events that preserved the causal structure but varied other perceptual features of the event. Studies 2 and 3 investigated 10‐month‐olds' interpretations of means‐end support sequences using both a habituation paradigm and a task that assessed infants' own means‐end actions. Whereas 10‐month‐olds failed to demonstrate an understanding of the causal structure when tested using a flat cloth as the support (Study 2), sensitivity to this structure was apparent when a rectangular box was the support. These patterns were evident in both action and perception (Study 3). Moreover, individual variation in action task performance was related to visual habituation performance. The results are discussed with respect to the relation between action and perception in infancy.     

Sex Differences in Infants' Ability to Represent Complex Event Sequences

Prior research suggests that when very simple event sequences are used, 4.5‐month‐olds demonstrate the ability to individuate objects based on the continuity or disruption of their speed of motion (Wilcox & Schweinle, 2003). However, infants demonstrate their ability to individuate objects in an event‐monitoring task (i.e., infants must keep track of an ongoing event) at a younger age than in an event‐mapping task (i.e., infants must compare information from 2 different events). The research presented here built on these findings by examining infants' capacity to succeed on an event‐mapping task with a more complex event sequence to determine if the complexity of the event interferes with their ability to form summary representations of the event, and, in short, individuate the objects. Three experiments were conducted with infants 4.5 to 9.5 months of age. The results indicated that (a) increasing the complexity of the objects' trajectories adversely affected infants' performance on the task, and (b) boys were more likely to succeed than girls. These findings shed light on how representational capacities change during the first year of life and are discussed in terms of information processing and representational capabilities as well as neuro‐anatomical development.     

Age‐Specific Preferences for Infant‐Directed Affective Intent

This study examined the developmental course of infants' attentional preferences for 3 types of infant‐directed affective intent, which have been shown to be commonly used at particular ages in the first year of life. Specifically, Kitamura and Burnham (2003) found mothers' tone of voice in infant‐directed speech is most comforting between birth and 3 months, most approving at 6 months, and most directive at 9 months. Thus, the aim of this study was to assess whether there is a relation between the type of affective intent used by mothers at each age point, and infants' affective intent preferences. Each infant group, 3‐, 6‐, and 9‐month‐olds, was played the 3 types of affective intent alternating across a single test session. When analyzed across age, the interactions revealed the predicted developmental trajectory; that is, infant preferences transformed between 3 and 6 months from comforting to approving, and between 6 and 9 months, from approving to directive. However, when analyzed separately by age, it was shown that 3‐month‐olds preferred comforting to other types; 6‐month‐olds preferred approving to directive, but listened equally to approving and comforting; and 9‐month‐olds showed no preference for any type of affective intent. Because it was possible that 9‐month‐olds were more focused on phonetic and phonotactic information, a new group of 9‐month‐olds was tested with intonation‐only versions of the 3 affective intent types. Under these conditions, they were found to prefer directive to comforting, but not directive to approving types. The results of this study have implications for what infants pay attention to in their social and linguistic environment over the course of the first year.     

Relation of infants' and mothers' pointing to infants' vocabulary measured directly and with parental reports

Infants' and parents' pointing gestures predict infants' concurrent and prospective language development. Most studies have measured vocabulary size using parental reports. However, parents tend to underestimate or overestimate infants' vocabulary necessitating the use of direct measures alongside parent reports. The present study examined whether mothers' index-finger pointing, and infants' whole-hand and index-finger pointing at 14 months associate with infants' receptive and expressive vocabulary based on parental reports and directly measured lexical processing efficiency (LPE) concurrently at 14 months and prospectively at 18 months. We used the decorated room paradigm to measure pointing frequency, the Turkish communicative development inventory I to measure infants' receptive vocabulary, Turkish communicative development inventory II to measure their expressive vocabulary, and the Looking-While-Listening (LWL) task to measure LPE. At 14 months, 34 mother-infant dyads, and at 18 months, 30 dyads were included in the analyses. We found that only infants' index-finger pointing frequency at 14 months predicted their LPE (both reaction time and accuracy) prospectively at 18 months but not concurrently at 14 months. Neither maternal pointing nor infants' pointing predicted their receptive and expressive vocabulary based on indirect measurement. The results extend the evidence on the relation between index-finger pointing and language development to a more direct measure of vocabulary.     

The Development of Specialized Processing of Own‐Race Faces in Infancy

In this study, we examined developmental changes in infants' processing of own‐ versus other‐race faces. Caucasian American 8‐month‐olds (Experiment 1) and 4‐month‐olds (Experiment 2) were tested in a habituation‐switch procedure designed to assess holistic (attending to the relationship between internal and external features of the face) versus featural (attending to individual features of the face) processing of faces. Eight‐month‐olds demonstrated holistic processing of upright own‐race (Caucasian) faces, but featural processing of upright other‐race (African) faces. Inverted faces were processed featurally, regardless of ethnicity. Four‐month‐olds, however, demonstrated holistic processing of both Caucasian and African upright faces. These results demonstrate that infants' processing of own‐ versus other‐race faces becomes specialized between 4 and 8 months.     

Recognition and Representation of Function Words in English‐Learning Infants

We examined infants' recognition of functors and the accuracy of the representations that infants construct of the perceived word forms. Auditory stimuli were “Functor + Content Word” versus “Nonsense Functor + Content Word” sequences. Eight‐, 11‐, and 13‐month‐old infants heard both real functors and matched nonsense functors (prosodically analogous to their real counterparts but containing a segmental change). Results reveal that 13‐month‐olds recognized functors with attention to segmental detail. Eight‐month‐olds did not distinguish real versus nonsense functors. The performance of 11‐month‐olds fell in between that of the older and younger groups, consistent with an emerging recognition of real functors. The three age groups exhibited a clear developmental trend. We propose that in the earliest stages of vocabulary acquisition, function elements receive no segmentally detailed representations, but such representations are gradually constructed so that once vocabulary growth starts in earnest, fully specified functor representations are in place to support it.     

Mothers’ Work Status and 17‐Month‐Olds’ Productive Vocabulary

Literature examining the effects of mothers’ work status on infant language development is mixed, with little focus on varying work schedules and early vocabulary. We use naturalistic data to analyze the productive vocabulary of 44 17‐month‐olds in relation to mothers’ work status (full time, part time, stay at home) at 6 and 18 months. Infants who experienced a combination of care from mothers and other caretakers had larger productive vocabularies than infants in solely full‐time maternal or solely other‐caretaker care. Our results draw from naturalistic data to suggest that this care combination may be particularly beneficial for early lexical development.     

Attention to Maternal Multimodal Naming by 6‐ to 8‐Month‐Old Infants and Learning of Word–Object Relations

We examined whether mothers' use of temporal synchrony between spoken words and moving objects, and infants' attention to object naming, predict infants' learning of word–object relations. Following 5 min of free play, 24 mothers taught their 6‐ to 8‐month‐olds the names of 2 toy objects, Gow and Chi, during a 3‐min play episode. Infants were then tested for their word mapping. The videotaped episodes were coded for mothers' object naming and infants' attention to different naming types. Results indicated that mothers' use of temporal synchrony and infants' attention during play covaried with infants' word‐mapping ability. Specifically, infants who switched eye gaze from mother to object most frequently during naming learned the word–object relations. The findings suggest that maternal naming and infants' word‐mapping abilities are bidirectionally related. Variability in infants' attention to maternal multimodal naming explains the variability in early lexical‐mapping development.     

Eighteen‐Month‐Olds,but not 14‐Month‐Olds,Use Social Context to Bind Action Sequences

We demonstrate that 18‐month‐olds, but not 14‐month‐olds, can anticipate others' actions based on an interpretation of shared goals that bind together individual actions into a collaborative sequence. After viewing a sequence of actions performed by two people who socially interact, 18‐month‐olds bound together the socially engaged actors' actions such that they later expected the actors to share the same final goal. Eighteen‐month‐olds who saw nonsocially engaged actors did not have this expectation and neither did 14‐month‐olds when viewing either socially or nonsocially engaged actors. The results are discussed in light of the possibility that experience in collaborations could be necessary for understanding collaboration from a third‐person perspective.     

Nineteen‐Month‐Olds' Understanding of the Conventionality of Object Labels Versus Desires

We assessed 19‐month‐olds' appreciation of the conventional nature of object labels versus desires. Infants played a finding game with an experimenter who stated her intention to find the referent of a novel word (word group), to find an object she wanted (desire group), or simply to look in a box (control group). A 2nd experimenter then administered a comprehension task to assess infants' tendency to extend information to a 2nd person who was not present at the time of learning. Results indicate that infants chose the target object when the 2nd experimenter asked for the referent of the novel label but not when she requested the referent of her desire. These findings demonstrate that 19‐month‐olds understand that words are conventional, but desires are not.     

Is Agency Skin Deep? Surface Attributes Influence Infants' Sensitivity to Goal‐Directed Action

Three studies investigated the role of surface attributes in infants' identification of agents, using a habituation paradigm designed to tap infants' interpretation of grasping as goal directed (Woodward, 1998). When they viewed a bare human hand grasping objects, 7‐ and 12‐month‐old infants focused on the relation between the hand and its goal. When the surface properties of the hand were obscured by a glove, however, neither 7‐ nor 12‐month‐old infants represented its actions as goal directed (Study 1). Next, infants were shown that the gloved hands were part of a person either prior to (Study 2) or during (Study 3) the habituation procedure. Infants who actively monitored the gloved person in Study 2 and older infants in Study 3 interpreted the gloved reaches as goal directed. Thus, varying the extent to which an entity is identifiable as a person impacts infants' interpretation of the entity as an agent.     

The Value of Vocalizing: 10‐Month‐Olds' Vocal Usage Relates to Language Outcomes at 15 Months

The interaction between infant's communicative competence and responsiveness of caregivers facilitates the transition from prelinguistic to linguistic communication. It is thus important to know how infants' communicative behavior changes in relation to different caregiver responses; furthermore, how infants' modification of communicative behavior relates to language outcomes. We investigated 39 10‐month‐old infants' communication as a function of mothers' attention and responses and the relationship to language outcomes at 15 months. We elicited infants' communicative behavior in three conditions: (1) joint attention: Mothers were visually attending and responding to infants' attention and interest; (2) available: Mothers were visually attending to infants, but not responding contingently to infants' attention and interest; (3) unavailable: Mothers were not attending to infants nor responding to them. Infants vocalized more when mothers attended and responded to them (conditions 1 and 2) than when mothers did not (condition 3), but infants' gesture and gesture‐vocal production did not differ across conditions. Furthermore, infants' production of a higher proportion of vocalizations in the unavailable condition relative to the joint attention condition correlated with, and predicted, infants' language scores at 15 months. Thus, infants who appear to be aware of the social effects of vocalizations may learn words better.     

Pointing to Nothing? Empty Places Prime Infants' Attention to Absent Objects

People routinely point to empty space when referring to absent entities. These points to “nothing” are meaningful because they direct attention to places that stand in for specific entities. Typically, the meaning of places in terms of absent referents is established through preceding discourse and accompanying language. However, it is unknown whether nonlinguistic actions can establish locations as meaningful places, and whether infants have the capacity to represent a place as standing in for an object. In a novel eye‐tracking paradigm, 18‐month‐olds watched objects being placed in specific locations. Then, the objects disappeared and a point directed infants' attention to an emptied place. The point to the empty place primed infants in a subsequent scene (in which the objects appeared at novel locations) to look more to the object belonging to the indicated place than to a distracter referent. The place–object expectations were strong enough to interfere when reversing the place–object associations. Findings show that infants comprehend nonlinguistic reference to absent entities, which reveals an ontogenetic early, nonverbal understanding of places as representations of absent objects.     

Seven‐Month‐Old Infants Selectively Reproduce the Goals of Animate But Not Inanimate Agents

We tested 7‐month‐old infants' sensitivity to others' goals in an imitation task, and assessed whether infants are as likely to imitate the goals of nonhuman agents as they are to imitate human goals. In the current studies, we used the paradigm developed by Hamlin et. al (in press) to test infants' responses to human actions versus closely matched inanimate object motions. The experimental events resembled those from Luo and Baillargeon's (2005) looking‐time study in which infants responded to the movements of an inanimate object (a self‐propelled box) as goal‐directed. Although infants responded visually to the goal structure of the object's movement, here they did not reproduce the box's goal. These results provide further evidence that 7‐month‐olds' goal representations are sufficiently robust to drive their own manual actions. However, they indicate that infants' responses to inanimate object movements may not be robust in this way.     

Bimodal Dynamics of Faces and Voices Influence Older Infants' Perception of Emotion

Given the importance of infants' perception of bimodal speech for emerging language and emotion development, this study used eye‐tracking technology to examine infants' attention to face+voice displays differing by emotion (fear, sad, happy) and visual stimulus (dynamic versus static). Peripheral distracters were presented to measure attention disengagement. It was predicted that infants would look longer at and disengage more slowly from dynamic bimodal emotion displays, especially when viewing dynamic fear. However, the results from twenty‐two 10‐month‐olds found significantly greater attention on dynamic versus static trials, independent of emotion. Interestingly, infants looked equally to mouth and eye regions of speakers' faces except when viewing/hearing dynamic fear; in this case, they fixated more on the speakers' mouth region. Average latencies to distracters were longer on dynamic compared to static bimodal stimuli, but not differentiated by emotion. Thus, infants' attention was enhanced (in terms of both elicitation and maintenance) by dynamic, bimodal emotion displays. Results are compared to conflicting findings using static emotion displays, with suggestions for future research using more ecologically relevant dynamic, multimodal displays to gain a richer understanding of infants' processing of emotion.     

Developmental Differences in Infants' Attention to Social and Nonsocial Threats

Research has demonstrated that humans detect threatening stimuli more rapidly than nonthreatening stimuli. Although the literature presumes that biases for threat should be normative, present early in development, evident across multiple forms of threat, and stable across individuals, developmental work in this area is limited. Here, we examine the developmental differences in infants' (4‐ to 24‐month‐olds) attention to social (angry faces) and nonsocial (snakes) threats using a new age‐appropriate dot‐probe task. In Experiment 1, infants' first fixations were more often to snakes than to frogs, and they were faster to fixate probes that appeared in place of snakes vs. frogs. There were no significant age differences, suggesting that a perceptual bias for snakes is present early in life and stable across infancy. In Experiment 2, infants fixated probes more quickly after viewing any trials that contained an angry face compared to trials that contained a happy face. Further, there were age‐related changes in infants' responses to face stimuli, with a general increase in looking time to faces before the probe and an increase in latency to fixate the probe after seeing angry faces. Together, this work suggests that different developmental mechanisms may be responsible for attentional biases for social vs. nonsocial threats.     

Can a Click be a Word?: Infants' Learning of Non‐Native Words

Forms that are nonlinguistic markers in one language (i.e., “tsk‐tsk” in English) may be part of the phoneme inventory—and hence part of words—in another language. In the current paper, we demonstrate that infants' ability to learn words containing unfamiliar language sounds is influenced by the age and vocabulary size of the infant learner, as well as by cues to the speaker's referential intent. When referential cues were available, infants at 14 months learned words with non‐native speech sounds, but at 20 months only those infants with smaller vocabularies succeeded. When no referential cues were present, infants at both 14 and 20 months failed to learn the same words. The implications of the relation between linguistic sophistication and non‐native word learning are discussed.     

The Cat is out of the Bag: The Joint Influence of Previous Experience and Looking Behavior on Infant Categorization

We examined the effect of 4‐month‐old infants' previous experience with dogs, cats, or both and their online looking behavior on their learning of the adult‐defined category of cat in a visual familiarization task. Four‐month‐old infants' (N = 123) learning in the laboratory was jointly determined by whether or not they had experience with pets at home and how much they shifted their gaze back and forth between the stimuli during familiarization. Specifically, only infants with pets at home who also exhibited high levels of switching during familiarization remembered the individual cat exemplars or formed a summary representation of those cats. These results are consistent with recent theorizing about the processes of how infants' categorical representations are formed, and provide new understanding into how infants' categorization unfolds over time.     

2‐Year‐Olds’ Speech Understanding in Multitalker Environments

Infants and toddlers are often spoken to in the presence of background sounds, including speech from other talkers. Prior work has suggested that infants 1 year of age and younger can only recognize speech when it is louder than any distracters in the environment. The present study tests 24‐month‐olds’ ability to understand speech in a multitalker environment. Children were presented with a preferential‐looking task in which a target voice told them to find one of two objects. At the same time, multitalker babble was presented as a distracter, at one of four signal‐to‐noise ratios. Children showed some ability to understand speech and look at the appropriate referent at signal‐to‐noise ratios as low as ?5 dB. These findings suggest that 24‐month‐olds are better able to selectively attend to an interesting voice in the context of competing distracter voices than are younger infants. There were significant correlations between individual children’s performance and their vocabulary size, but only at one of the four noise levels; thus, it does not appear that vocabulary size is the driving factor in children’s listening improvement, although it may be a contributing factor to performance in noisy environments.     

The Influence of Labels,Non‐Labeling Sounds,and Source of Auditory Input on 9‐ and 15‐Month‐Olds' Object Categorization

This experiment examines the joint influence of auditory and social cues on infants' basic‐level and global categorization. Nine‐ and fifteen‐month‐olds were familiarized to a series of category exemplars in an object‐examining task. Objects were introduced with a labeling phrase, a non‐labeling sound, or no sound, and auditory input was presented orally by the experimenter or played on a hidden voice recorder. Novel objects from the familiarized category and a contrasting category were then presented. Results of analyses performed on novelty preference scores indicated that infants demonstrated basic‐level categorization in all conditions. However, infants at both age levels only demonstrated global categorization when labeling phrases were introduced. In addition, labels led to global categorization in 9‐month‐olds regardless of the source of those labels; however, labels only led to global categorization in 15‐month‐olds when the labels were presented orally by the experimenter.