English‐Learning Infants' Representations of Word Forms With Iambic Stress

Retaining detailed representations of unstressed syllables is a logical prerequisite for infants' use of probabilistic phonotactics to segment iambic words from fluent speech. The head‐turn preference study was used to investigate the nature of English‐learners' representations of iambic word onsets. Fifty‐four 10.5‐month‐olds were familiarized to passages containing the nonsense iambic word forms ginome and tupong. Following familiarization, infants were either tested on familiar (ginome and tupong) or near‐familiar (pinome and bupong) versus unfamiliar (kidar and mafoos) words. Infants in the familiar test group (familiar vs. unfamiliar) oriented significantly longer to familiar than unfamiliar test items, whereas infants in the near‐familiar test group (near‐familiar vs. unfamiliar) oriented equally long to near‐familiar and unfamiliar test items. Our results provide evidence that infants retain fairly detailed representations of unstressed syllables and therefore support the hypothesis that infants use phonotactic cues to find words in fluent speech.     

Effects of Familiarity and Feeding on Newborn Speech–Voice Recognition

Newborn infants preferentially orient to familiar over unfamiliar speech sounds. They are also better at remembering unfamiliar speech sounds for short periods of time if learning and retention occur after a feed than before. It is unknown whether short‐term memory for speech is enhanced when the sound is familiar (versus unfamiliar) and, if so, whether the effect is further enhanced by feeding. We used a two‐factorial design and randomized infants to one of four groups: prefeed‐unfamiliar, prefeed‐familiar, postfeed‐unfamiliar, and postfeed‐familiar. Memory for either familiar or unfamiliar speech (the infant's mother saying “baby” versus a female stranger saying “beagle”) was assessed using head turning to sound in an habituation–recovery paradigm and a retention delay of 85 sec either before or after a typical milk feed. Memory for the familiar speech–voice was enhanced relative to the unfamiliar speech–voice, expressed by significantly less head turning toward the habituated sound stimulus when it was re‐presented after the delay. Memory for familiar or unfamiliar speech was not significantly enhanced from pre‐ to postfeeding, nor was there a significant interaction. This is the first demonstration in newborns that familiarity enhances short‐term memory for speech–voice sound.     

What aspects of counting help infants attend to numerosity?

Recent work shows that 18-month old infants understand that counting is numerically relevant—infants who see objects counted are more likely to represent the approximate number of objects in the array than infants who see the objects labeled but not counted. Which aspects of counting signal infants to attend to numerosity in this way? Here we asked whether infants rely on familiarity with the count words in their native language, or on procedures instantiated by the counting routine, independent of specific tokens. In three experiments (N = 48), we found that 18-month old infants from English-speaking households successfully distinguished four hidden objects from two when the objects were counted correctly, regardless of their familiarity with the count words (i.e., when objects were counted in familiar English and in unfamiliar German). However, when the objects were counted using familiar English count words in ways that violated basic counting principles, infants no longer represented the arrays, failing to distinguish four hidden objects from two. Together with previous findings, these results suggest that children may link the procedure of counting with numerosity years before they learn the meanings of the count words.     

Neural Correlates of Human and Monkey Face Processing in 9‐Month‐Old Infants

Behavioral and electrophysiological evidence suggests a gradual, experience‐dependent specialization of cortical face processing systems that takes place largely in the 1st year of life. To further investigate these findings, event‐related potentials (ERPs) were collected from typically developing 9‐month‐old infants presented with pictures of familiar and unfamiliar monkey or human faces in 2 different orientations. Analyses revealed differential processing across changes in monkey and human faces. The N290 was greater for familiar compared to unfamiliar faces, regardless of species or orientation. In contrast, the P400 to unfamiliar faces was greater than to familiar faces, but only for the monkey condition. The P400 to human faces differentiated the orientation of both familiar and unfamiliar faces. These results suggest more specific processing of human compared to monkey faces in 9‐month‐olds.     

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.     

Crawling Predicts Infants’ Understanding of Agents’ Navigation of Obstacles

We investigated whether crawling versus noncrawling infants interpret an agent's movements around an obstacle as goal‐directed. Infants (6–9 months) were habituated to a self‐propelled circle jumping over an obstacle to reach a goal. When the obstacle was removed, infants who crawled (n = 13) showed longer looking time to the familiar but now nonrational jumping path versus a novel but rational straight‐line path. Noncrawlers (n = 17) did not discriminate. Looking preference was independent of age and speed of habituation. These findings support the claim that infants’ processing of agency emerges early and applies to all agents, but stress the role of experience in the development of action interpretation.     

A Comparative Study of Arm‐Restraint Methodology: Differential Effects of Mother and Stranger Restrainers on Infants' Distress Reactivity at 6 and 9 Months of Age

This study examined both differential patterns and the stability of infants' (N = 70) distress reactivity across mother and stranger arm‐restraint conditions when infants were 6 and 9 months of age. Reactivity measures included observational variables for the rise, intensity, and duration of infant distress as well as motor activities associated with escape behaviors. Correlation analyses revealed that infant behaviors during arm restraint were modestly stable across conditions and over time; however, mean comparisons also showed that infants' distress responses appear to be sensitive to protocol parameters (whether restrainer is mother or stranger). At 6 months of age, infants cried more during maternal restraint than with strangers and exhibited escape behaviors more frequently with mothers. Findings further indicate that infants' distress reactivity undergoes developmental alterations from 6 to 9 months of age, with infants crying more quickly, reaching peak intensity of distress faster, and displaying more distress at 9 months compared to 6 months. These changes in infants' reactivity were particularly accentuated during maternal compared to stranger restraint conditions at 9 months of age.     

Interacting Socially With Human Hands at 24 Months of Age

This experiment explored whether or not 2‐year‐olds would engage in synchronic imitation with human hands. Sixty‐four 24‐month‐old infants participated. In a test of synchronic imitation, infants were given a toy while a model simultaneously performed novel actions on an identical toy. Infants were randomly assigned to 1 of 4 model conditions: a familiar person, an unfamiliar person, disembodied human hands, and disembodied robotic pincers. Infants were as likely to synchronically imitate disembodied hands as a person. Imitation of the pincers was significantly lower. This pattern suggests that 2‐year‐olds will engage socially with human hands in the absence of the rest of the body.     

Word Level Stress and Lexical Processing in 17‐Month‐Old Infants

Detailed representations enable infants to distinguish words from one another and more easily recognize new words. We examined whether 17‐month‐old infants encode word stress in their familiar word representations. In Experiment 1, infants were presented with pairs of familiar objects while hearing a target label either properly pronounced with the correct stress (e.g., baby /’be?bi/) or mis‐pronounced with the incorrect stress pattern (e.g., baby /be?’bi/). Infants mapped both the correctly stressed and mis‐stressed labels to the target objects; however, they were slower to fixate the target when hearing the mis‐stressed label. In Experiment 2, we examined whether infants appreciate that stress has a nonproductive role in English (i.e., altering the stress of a word does not typically signal a change in word meaning) by presenting infants with a familiar object paired with a novel object while hearing either correctly stressed or mis‐stressed familiar words (Experiment 2). Here, infants mapped the correctly stressed label to the familiar object but did not map the mis‐stressed label reliably to either the target or distractor objects. These findings suggest that word stress impacts the processing of familiar words, and infants have burgeoning knowledge that altering the stress pattern of a familiar word does not reliably signal a new referent.     

An object's categorizability impacts whether infants encode surface features into their object representations

Infants encode the surface features of simple, unfamiliar objects (e.g., red triangle) and the categorical identities of familiar, categorizable objects (e.g., car) into their representations of these objects. We asked whether 16–18-month-olds ignore non-diagnostic surface features (e.g., color) in favor of encoding an object's categorical identity (e.g., car) when objects are from familiar categories. In Experiment 1 (n = 18), we hid a categorizable object inside an opaque box. In No Switch trials, infants retrieved the object that was hidden. In Switch trials, infants retrieved a different object: an object from a different category (Between-Category-Switch trials) or a different object from the same category (Within-Category-Switch trials). We measured infants' subsequent searching in the box. Infants' pattern of searching suggested that only infants who completed a Within-Category-Switch trial as their first Switch trial encoded objects' surface features, and an exploratory analysis suggested that infants who completed a Between-Category-Switch trial as their first Switch trial only encoded objects' categories. In Experiment 2 (n = 18), we confirmed that these results were due to objects' categorizability. These results suggest infants may tailor the way they encode categorizable objects depending on which object dimensions are perceived to be task relevant.     

Affective and Behavioral Features of Jealousy Protest: Associations with Child Temperament,Maternal Interaction Style,and Attachment

This study explored variation in affective and behavioral components of infants’ jealousy protests during an eliciting condition in which mother and an experimenter directed differential attention exclusively toward a rival. Variation was examined in relation to child temperamental emotionality, maternal interaction style, and attachment security. At 45 weeks, intensity of infants’distress and durations of mother‐ and stranger‐directed behavioral responses, including gaze, touch, and proximity‐seeking, were observed in the eliciting condition. We also assessed infants’positive emotionality (PE) and negative emotionality (NE) and maternal interaction styles of sensitivity and engagement. At 54 weeks, attachment security was measured in the Strange Situation Procedure. Findings revealed that distress differed with temperamental emotionality and maternal interaction style. Specifically, distress was greater in infants with lower PE and having mothers who displayed less sensitivity and engagement. Analyses on behavioral responses toward the experimenter revealed linkages with maternal interaction style. Specifically, experimenter‐directed gaze and touch were greater among infants of mothers who demonstrated less sensitivity and engagement. Behavioral responses toward mother were found associated with quality of attachment. Specifically, mother‐directed proximity and touch were highest among infants later judged insecure resistant and lowest among those later judged insecure/avoidant; with infants later judged secure displaying moderate durations of mother‐directed proximal contact.     

Resolving the (Apparent) Talker Recognition Paradox in Developmental Speech Perception

The infant literature suggests that humans enter the world with impressive built‐in talker processing abilities. For example, newborns prefer the sound of their mother's voice over the sound of another woman's voice, and well before their first birthday, infants tune in to language‐specific speech cues for distinguishing between unfamiliar talkers. The early childhood literature, however, suggests that preschoolers are unable to learn to identify the voices of two unfamiliar talkers unless these voices are highly distinct from one another, and that adult‐level talker recognition does not emerge until children near adolescence. How can we reconcile these apparently paradoxical messages conveyed by the infant and early childhood literatures? Here, we address this question by testing 16.5‐month‐old infants (N = 80) in three talker recognition experiments. Our results demonstrate that infants at this age have difficulty recognizing unfamiliar talkers, suggesting that talker recognition (associating voices with people) is mastered later in life than talker discrimination (telling voices apart). We conclude that methodological differences across the infant and early childhood literatures—rather than a true developmental discontinuity—account for the performance differences in talker processing between these two age groups. Related findings in other areas of developmental psychology are discussed.     

Picture Perception in Infants: Generalization From Two‐Dimensional to Three‐Dimensional Displays

Two experiments investigated 9‐month‐old infants’ abilities to recognize the correspondence between an actual three‐dimensional (3D) object and its two‐dimensional (2D) representation, looking specifically at representations that did not literally depict the actual object: schematic line drawings. In Experiment 1 , infants habituated to a line drawing of either a doll or a sheep and were then tested with the actual objects themselves. Infants habituated to the sheep drawing recovered to the unfamiliar but not the familiar object, showing a novelty preference. Infants habituated to the doll drawing, however, recovered to both familiar and unfamiliar objects, failing to show any preference between the two. In Experiment 2 , infants habituated to the 3D objects and were then tested with the 2D line drawings. In this case, both groups of infants showed a preference only for the novel displays. Together these findings demonstrate that 9‐month‐old infants recognize the correspondence between 3D objects and their 2D representations, even when these representations are not literal copies of the objects themselves.     

The Other‐Race Effect in Infancy: Evidence Using a Morphing Technique

Human adults are more accurate at discriminating faces from their own race than faces from another race. This other‐race effect (ORE) has been characterized as a reflection of face processing specialization arising from differential experience with own‐race faces. We examined whether 3.5‐month‐old infants exhibit ORE using morphed faces on which adults had displayed a crossover ORE (i.e., Caucasians performed better on Caucasian faces and Asians performed better on Asian faces). In this experiment, Caucasian infants who had grown up in a predominantly Caucasian environment discriminated 100% Caucasian faces from 70% Caucasian/30% Asian morphed faces but failed to discriminate between the corresponding 100% Asian and 70% Asian/30% Caucasian faces. Thus, 3.5‐month‐olds exhibited evidence of ORE. These results indicate that at least by 3.5 months of age, infants have attained enough face processing expertise to process familiar‐race faces in a different manner than unfamiliar‐race faces.     

A Privileged Status for Male Infant‐Directed Speech in Infants of Depressed Mothers? Role of Father Involvement

Prior research showed that 5‐ to 13‐month‐old infants of chronically depressed mothers did not learn to associate a segment of infant‐directed speech produced by their own mothers or an unfamiliar nondepressed mother with a smiling female face, but showed better‐than‐normal learning when a segment of infant‐directed speech produced by an unfamiliar nondepressed father signaled the face. Here, learning in response to an unfamiliar nondepressed father’s infant‐directed speech was studied as a function both of the mother’s depression and marital status, a proxy measure of father involvement. Infants of unmarried mothers on average did not show significant learning in response to the unfamiliar nondepressed father’s infant‐directed speech. Infants of married mothers showed significant learning in response to male infant‐directed speech, and infants of depressed, married mothers showed significantly stronger learning in response to that stimulus than did infants of nondepressed, married mothers. Several ways in which father involvement may positively or negatively affect infant responsiveness to male infant‐directed speech are discussed.     

Beneficial effects of the mother's voice on infants’ novel word learning

The maternal voice appears to have a special role in infants’ language processing. The current eye‐tracking study investigated whether 24‐month‐olds (n = 149) learn novel words easier while listening to their mother's voice compared to hearing unfamiliar speakers. Our results show that maternal speech facilitates the formation of new word–object mappings across two different learning settings: a live setting in which infants are taught by their own mother or the experimenter, and a prerecorded setting in which infants hear the voice of either their own or another mother through loudspeakers. Furthermore, this study explored whether infants’ pointing gestures and novel word productions over the course of the word learning task serve as meaningful indexes of word learning behavior. Infants who repeated more target words also showed a larger learning effect in their looking behavior. Thus, maternal speech and infants’ willingness to repeat novel words are positively linked with novel word learning.     

Infants Experience Perceptual Narrowing for Nonprimate Faces

Perceptual narrowing—a phenomenon in which perception is broad from birth, but narrows as a function of experience—has previously been tested with primate faces. In the first 6 months of life, infants can discriminate among individual human and monkey faces. Though the ability to discriminate monkey faces is lost after about 9 months, infants retain human face discrimination, presumably because of their experience with human faces. The current study demonstrates that 4‐ to 6‐month‐old infants are able to discriminate nonprimate faces as well. In a visual paired comparison test, 4‐ to 6‐month‐old infants (n = 26) looked significantly longer at novel sheep (Ovis aries) faces, compared to a familiar sheep face (p = .017), while 9‐ to 11‐month‐olds (n = 26) showed no visual preference, and adults (n = 27) had a familiarity preference (p < .001). Infants’ face recognition systems are broadly tuned at birth—not just for primate faces, but for nonprimate faces as well—allowing infants to become specialists in recognizing the types of faces encountered in their first year of life.     

The Organization of Words and Symbolic Gestures in 18‐Month‐Olds’ Lexicons: Evidence From a Disambiguation Task

Infants’ early communicative repertoires include both words and symbolic gestures. The current study examined the extent to which infants organize words and gestures in a single unified lexicon. As a window into lexical organization, eighteen‐month‐olds’ (N = 32) avoidance of word–gesture overlap was examined and compared with avoidance of word–word overlap. The current study revealed that when presented with novel words, infants avoided lexical overlap, mapping novel words onto novel objects. In contrast, when presented with novel gestures, infants sought overlap, mapping novel gestures onto familiar objects. The results suggest that infants do not treat words and gestures as equivalent lexical items and that during a period of development when word and symbolic gesture processing share many similarities, important differences also exist between these two symbolic forms.     

Twelve‐Month‐Olds Know Their Cups From Their Keps and Tups

Fourteen‐month‐olds are sensitive to mispronunciations of the vowels and consonants in familiar words (N. Mani & K. Plunkett (2007), Journal of Memory and Language, 57, 252; D. Swingley & R. N. Aslin (2002), Psychological Science, 13, 480). To examine the development of this sensitivity further, the current study tests 12‐month‐olds’ sensitivity to different kinds of vowel and consonant mispronunciations of familiar words. The results reveal that vocalic changes influence word recognition, irrespective of the kinds of vocalic changes made. While consonant changes influenced word recognition in a similar manner, this was restricted to place and manner of articulation changes. Infants did not display sensitivity to voicing changes. Infants’ sensitivity to vowel mispronunciations, but not consonant mispronunciations, was influenced by their vocabulary size—infants with larger vocabularies were more sensitive to vowel mispronunciations than infants with smaller vocabularies. The results are discussed in terms of different models attempting to chart the development of acoustically or phonologically specified representations of words during infancy.     

Infants’ Discrimination of Familiar and Unfamiliar Accents in Speech

This study investigates infants’ discrimination abilities for familiar and unfamiliar regional English accents. Using a variation of the head‐turn preference procedure, 5‐month‐old infants demonstrated that they were able to distinguish between their own South‐West English accent and an unfamiliar Welsh English accent. However, this distinction was not seen when two unfamiliar accents (Welsh English and Scottish English) were presented to the infants, indicating they had not acquired the general ability to distinguish between regional varieties, but only the distinction between their home accent and unfamiliar regional variations. This ability was also confirmed with 7‐month‐olds, challenging recent claims that infants lose their sensitivity to dialects at around that age. Taken together, our results argue in favor of an early sensitivity to the intonation system of languages, and to the early learning of accent‐specific intonation and potentially segmental patterns. Implications for the development of accent normalization abilities are discussed.