Statistical word segmentation: Anchoring learning across contexts

The present experiments were designed to assess infants' abilities to use syllable co-occurrence regularities to segment fluent speech across contexts. Specifically, we investigated whether 9-month-old infants could use statistical regularities in one speech context to support speech segmentation in a second context. Contexts were defined by different word sets representing contextual differences that might occur across conversations or utterances. This mimics the integration of information across multiple interactions within a single language, which is critical for language acquisition. In particular, we performed two experiments to assess whether a statistically segmented word could be used to anchor segmentation in a second, more challenging context, namely speech with variable word lengths. The results of Experiment 1 were consistent with past work suggesting that statistical learning may be hindered by speech with word-length variability, which is inherent to infants' natural speech environments. In Experiment 2, we found that infants could use a previously statistically segmented word to support word segmentation in a novel, challenging context. We also present findings suggesting that this ability was associated with infants' early word knowledge but not their performance on a cognitive development assessment.     

Avoidance of Heights on the Visual Cliff in Newly Walking Infants

Work with infants on the “visual cliff” links avoidance of drop‐offs to experience with self‐produced locomotion. Adolph's (2002) research on infants' perception of slope and gap traversability suggests that learning to avoid falling down is highly specific to the postural context in which it occurs. Infants, for example, who have learned to avoid crossing risky slopes while crawling must learn anew such avoidance when they start walking. Do newly walking infants avoid crossing the drop‐off of the visual cliff? Twenty prewalking but experienced crawling infants were compared with 20 similarly aged newly walking infants on their reactions to the visual cliff. Newly walking infants avoided moving onto the cliff's deep side even more consistently than did the prewalking crawlers. Thus, in the context of drop‐offs in visual texture, our results show that once avoidance of drop‐offs is established under conditions of crawling, it is developmentally maintained once infants begin walking.     

Maternal Talk About Mental States and the Emergence of Joint Visual Attention

Twenty‐four infants were tested monthly for gaze and point following between 9 and 15 months of age and mother‐infant free play sessions were also conducted at 9, 12, and 15 months (Carpenter, Nagell, & Tomasello, 1998). Using this data set, this study explored relations between maternal talk about mental states during mothers' free play with their infants and the emergence of joint visual attention in infants. Contrary to hypothesis, mothers' comments about their infants' perceptual states significantly declined after their infants began to engage in joint visual attention. Comments about other mental states did not change relative to acquisition of joint visual attention skill. We speculate that after infants begin to reliably follow gaze and points, mothers may switch the focus of their conversation from their infants' visual behavior and experiences to the object of their mutual attention.     

Within‐rhythm Class Native Language Discrimination Abilities of Basque‐Spanish Monolingual and Bilingual Infants at 3.5 Months of Age

Language rhythm determines young infants' language discrimination abilities. However, it is unclear whether young bilingual infants exposed to rhythmically similar languages develop sensitivities to cross‐linguistic rhythm cues to discriminate their dual language input. To address this question, 3.5‐month‐old monolingual Basque, monolingual Spanish and bilingual Basque‐Spanish infants' language discrimination abilities (across low‐pass filtered speech samples of Basque and Spanish) have been tested using the visual habituation procedure. Although falling within the same rhythmic class, Basque and Spanish exhibit significant differences in their distributions of vocalic intervals (within‐rhythmic class variation). All infant groups in our study successfully discriminated between the languages, although each group exhibited a different pattern. Monolingual Spanish infants succeeded only when they heard Basque during habituation, suggesting that they were influenced by native language recognition. The bilingual and the Basque monolingual infants showed no such asymmetries and succeeded irrespective of the language of habituation. Additionally, bilingual infants exhibited longer looking times in the test phase as compared with monolinguals, reflecting that bilingual infants attend to their native languages differently than monolinguals. Overall, results suggest that bilingual infants are sensitive to within‐rhythm acoustic regularities of their native language(s) facilitating language discrimination and hence supporting early bilingual acquisition.     

Sensitivity to Word‐Final Phonotactics in 9‐ to 16‐Month‐Old Infants

Previous research has shown that infants begin to display sensitivities to language‐specific phonotactics and probabilistic phonotactics at around 9 months of age. However, certain phonotactic patterns have not yet been examined, such as contrast neutralization, in which phonemic contrasts are neutralized typically in syllable‐ or word‐final position. Thus, the acquisition of contrast neutralization is dependent on infants' ability to perceive certain contrasts in final position. The studies reported here test infants' sensitivity to voicing neutralization in word‐final position and infants' discrimination of voicing and place of articulation (POA) contrasts in word‐initial and word‐final position. Nine and 11‐month‐old Dutch‐learning infants showed no preference for legal versus illegal voicing phonotactics that were contrasted in word‐final position. Furthermore, 10‐month‐old infants showed no discrimination of voicing or POA contrasts in word‐final position, whereas they did show sensitivity to the same contrasts in word‐initial position. By 16 months, infants were able to discriminate POA contrasts in word‐final position, although showing no discrimination of the word‐final voicing contrast. These findings have broad implications for models of how learners acquire the phonological structures of their language, for the types of phonotactic structures to which infants are presumed to be sensitive, and for the relative sensitivity to phonemic distinctions by syllable and word position during acquisition.     

An Eye Tracking Investigation of Color–Location Binding in Infants' Visual Short‐Term Memory

Two experiments examined 8‐ and 10‐month‐old infants' (N = 71) binding of object identity (color) and location information in visual short‐term memory (VSTM) using a one‐shot change detection task. Building on previous work using the simultaneous streams change detection task, we confirmed that 8‐ and 10‐month‐old infants are sensitive to changes in binding between identity and location in VSTM. Further, we demonstrated that infants recognize specifically what changed in these events. Thus, infants' VSTM for binding is robust and can be observed in different procedures and with different stimuli.     

Learning Stimulus‐Location Associations in 8‐ and 11‐Month‐Old Infants: Multimodal Versus Unimodal Information

Research on the influence of multimodal information on infants' learning is inconclusive. While one line of research finds that multimodal input has a negative effect on learning, another finds positive effects. The present study aims to shed some new light on this discussion by studying the influence of multimodal information and accompanying stimulus complexity on the learning process. We assessed the influence of multimodal input on the trial‐by‐trial learning of 8‐ and 11‐month‐old infants. Using an anticipatory eye movement paradigm, we measured how infants learn to anticipate the correct stimulus–location associations when exposed to visual‐only, auditory‐only (unimodal), or auditory and visual (multimodal) information. Our results show that infants in both the multimodal and visual‐only conditions learned the stimulus–location associations. Although infants in the visual‐only condition appeared to learn in fewer trials, infants in the multimodal condition showed better anticipating behavior: as a group, they had a higher chance of anticipating correctly on more consecutive trials than infants in the visual‐only condition. These findings suggest that effects of multimodal information on infant learning operate chiefly through effects on infants' attention.     

Infants' Perception of Intonation: Is It a Statement or a Question?

The ability to distinguish phonetic variations in speech that are relevant to meaning is essential for infants' language development. Previous studies into the acquisition of prosodic categories have focused on lexical stress, lexical pitch accent, or lexical tone. However, very little is known about the developmental course of infants' perception of linguistic intonation. In this study, we investigate infants' perception of the correlates of the statement/yes–no question contrast in a language that marks this sentence type distinction only by prosodic means, European Portuguese (EP). Using a modified version of the visual habituation paradigm, EP‐learning infants at 5–6 and 8–9 months were able to successfully discriminate segmentally varied, single‐prosodic word intonational phrases presented with statement or yes–no question intonation, demonstrating that they are sensitive to the prosodic cues marking this distinction as early as 5 months and maintain this sensitivity throughout the first year. These results suggest the presence of precocious discrimination abilities for intonation across segmental variation, similarly to previous reports for lexical pitch accent, but unlike previous findings for word stress.     

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.     

Discrimination of Large and Small Numerosities by Human Infants

Six experiments investigated infants' sensitivity to numerosity in auditory sequences. In prior studies (Lipton & Spelke, 2003), 6‐month‐old infants discriminated sequences of 8 versus 16 but not 8 versus 12 sounds, and 9‐month‐old infants discriminated 8 versus 12 but not 8 versus 10 sounds, when the continuous variables of rate, sound duration, and sequence duration were controlled. The current studies investigated whether infants' numerical discrimination is subject to the signature ratio limit of adults' numerosity discrimination. Four experiments at 6 and 9 months provided evidence for this signature limit, suggesting that common mechanisms underlie numerosity discrimination in infants and adults. In further experiments, infants failed to discriminate 2 versus 4 or 2 versus 3 sounds when tested under the same conditions as with large numbers. These findings accord with studies using visual‐spatial arrays (e.g., Clearfield & Mix, 1999) and suggest that separate systems underlie infants' representation of small and large numerosities.     

Contribution of Motion Information to Maternal Face Discrimination in Infancy

The contribution of motion and feature invariant information in infants' discrimination of maternal versus female stranger faces was assessed. Using an infant controlled habituation–dishabituation procedure, 4‐ and 8‐month‐old infants (N = 62) were tested for their ability to discriminate between their mother and a female stranger in 4 different conditions varying whether motion or feature information about the faces was available. The faces were presented in a still or dynamic video image with either a positive or a negative contrast. In each condition, infants habituated to a stranger's face and then viewed, in 3 pairs of alternating novelty test trials, either a new stranger or their mother's face. Results show that motion information contributes to the 8‐month‐old infants', but not the 4‐month‐old infants' discrimination of maternal faces. These results are interpreted in relation to recent findings and models in the adult literature suggesting that there is an enhanced contribution of dynamic information in face recognition when the face is familiar. Our data confirm that from the outset, there is a complex interplay of feature and motion information in the discrimination of the mother's face when the viewing condition is not optimal.     

Temporal Sequence of Global‐Local Processing in 3‐Month‐Old Infants

In 3 experiments, the temporal processing sequence of local and global visual properties was investigated with 3‐month‐old infants. Across the experiments, a global pattern was discriminated under conditions of less familiarization than was necessary for local elements to be discriminated, thus indicating a global precedence in the sequence of visual processing at 3 months of age. Patterns of discrimination were also observed to vary as a function of individual differences in infants' look duration. Furthermore, the pattern of novelty and familiarity preferences for short‐looking infants varied in complex ways as a function of familiarization time: Preferences for novel global properties were supplanted by familiarity preferences at the point in familiarization at which infants first became sensitive to local properties.     

Infants' Manual Exploration of Pictorial Objects Varying in Realism

In previous research, we established that 9‐month‐old infants manually investigate pictured objects by hitting, rubbing, and grasping as if to pluck them off the page. This behavior suggests that infants do not understand the 2‐dimensional nature of pictures. Although they can perceive depth cues and distinguish pictures from objects, they do not appreciate the significance of these cues; that is, they do not realize how depicted objects differ from real ones. We report 2 studies that support the idea that infants' manual response to pictures is driven by the resemblance of depicted objects to the real objects they represent. In Study 1, we report that infants' manual investigation of pictures is directly related to how realistic they are: The more depicted objects look like real objects, the more manual investigation they evoke. In Study 2, we show that 9‐month‐old infants' manual behaviors are concentrated on depicted objects even when there are areas of greater perceptual contrast on the page. The results are discussed with respect to the early development of pictorial competence.     

Postural Position Constrains Multimodal Object Exploration in Infants

Recent research has revealed the important role of multimodal object exploration in infants' cognitive and social development. Yet, the real‐time effects of postural position on infants' object exploration have been largely ignored. In the current study, 5‐ to 7‐month‐old infants (N = 29) handled objects while placed in supported sitting, supine, and prone postures, and their spontaneous exploratory behaviors were observed. Infants produced more manual, oral, and visual exploration in sitting compared to lying supine and prone. Moreover, while sitting, infants more often coupled manual exploration with mouthing and visual examination. Infants' opportunities for learning from object exploration are embedded within a real‐time postural context that constrains the quantity and quality of exploratory behavior.     

Body Structure Perception in Infancy

Structural cues, such as the relative size and arrangement of parts, are key aspects of adults' representation of human bodies, and they are used to derive significant social information such as age, sex, and attractiveness. Prior studies have not clearly addressed young infants' sensitivity to these body characteristics. In the current experiments, 3.5‐month‐olds exhibited a preference between images of intact bodies versus those with parts in wrong locations. Infants also discriminated between intact bodies and those with distorted part proportions. In both cases, infants discriminated when images were presented upright but not when they were inverted. These results indicate that infants are sensitive to the arrangement and size of human body parts at least by 3.5 months of age. Thus, contrary to some prior reports, body representation early in life is developed enough to include structural information.     

Competition for Infants' Attention: The Interactive Influence of Attentional State and Stimulus Characteristics

The interactive effects of stimulus characteristics and attentional state on infants' distraction latency were studied. As 7‐month‐old infants explored initial stimuli that were composed of either a single nonmoving component or multiple moving components, one of several types of distractors was presented in the periphery. Infants' distraction latencies (the amount of time they took to turn from the initial stimulus to the distractor) varied as a function of the interaction between the infants' attentional state at distractor onset and the characteristics of the stimuli. Variations in the visual characteristics of the distractor stimulus (solid rectangle vs. checkerboard) had a larger effect on distraction latency when infants were in a focused attentional state than when they were in a casual attentional state. Similarly, variations in the auditory characteristic of the distractor stimulus (1 intermittent tone vs. 2 alternating tones) had a larger effect when infants were engaged in a focused attentional state toward the multicomponent toys. Thus, infants' distractibility in this context reflects an interaction between the infants' attentional state and the competition between external stimuli for their attentional focus.     

Infants Associate Praise and Admonishment with Fair and Unfair Individuals

Recent evidence suggests that infants possess a rudimentary sensitivity to fairness: Infants expect resources to be distributed fairly and equally, and prefer individuals that distribute resources fairly over those that do so unfairly. The goal of this work was to determine whether infants' evaluations of fair and unfair individuals also includes an understanding that fair individuals are worthy of praise and unfair individuals are worthy of admonishment. After watching individuals distribute goods fairly or unfairly to recipients, 15‐month‐old (Experiments 1 and 2) and 13‐month‐old (Experiment 3) infants took part in a test phase in which they saw only the distributors' faces accompanied by praise or admonishment. Across all experiments, infants differentially shifted their visual attention to images of the fair and unfair distributors as a function of the accompanying praise or admonishment, although the direction in which they did so varied by age. Thus, by the start of the second year of life, infants appear to perceive fair individuals as morally praiseworthy and unfair individuals as morally blameworthy.     

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.     

12‐Month‐Old Infants' Perception of Attention Direction in Static Video Images

Twelve‐month‐old infants' ability to perceive gaze direction in static video images was investigated. The images showed a woman who performed attention‐directing actions by looking or pointing toward 1 of 4 objects positioned in front of her (2 on each side). When the model just pointed at the objects, she looked straight ahead, and when she just looked, her hands were hidden below the tabletop. An eye movement system (TOBII) was used to register the gaze of the participants. We found that the infants clearly discriminated the gaze directions to the objects. There was no tendency to mix up the 2 object positions, located 10° apart, on the same side of the model. The infants spent more time looking at the attended objects than the unattended ones and they shifted gaze more often from the face of the model to the attended object than to the unattended objects. Pointing did not significantly increase the infants' tendency to move gaze to the attended object, irrespective of whether the pointing gesture was accompanied by looking or not. In all conditions the infants spent most of the time looking at the model's face. This tendency was especially noticeable in the pointing‐only condition and the condition where the model just looked straight ahead.     

Early Word Segmentation in Naturalistic Environments: Limited Effects of Speech Register

We examined 7.5‐month‐old infants' ability to segment words from infant‐ and adult‐directed speech (IDS and ADS). In particular, we extended the standard design of most segmentation studies by including a phase where infants were repeatedly exposed to target word recordings at their own home (extended exposure) in addition to a laboratory‐based familiarization. This enabled us to examine infants' segmentation of words from speech input in their naturalistic environment, extending current findings to learning outside the laboratory. Results of a modified preferential‐listening task show that infants listened longer to isolated tokens of familiarized words from home relative to novel control words regardless of register. However, infants showed no recognition of words exposed to during purely laboratory‐based familiarization. This indicates that infants succeed in retaining words in long‐term memory following extended exposure and recognizing them later on with considerable flexibility. In addition, infants segmented words from both IDS and ADS, suggesting limited effects of speech register on learning from extended exposure in naturalistic environments. Moreover, there was a significant correlation between segmentation success and infants' attention to ADS, but not to IDS, during the extended exposure phase. This finding speaks to current language acquisition models assuming that infants' individual attention to language stimuli drives successful learning.