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.     

Global‐Before‐Basic Object Categorization in Connectionist Networks and 2‐Month‐Old Infants

A 3‐layered backpropagation connectionist network, configured as an autoassociator, learned to form global (e.g., mammal) before basic‐level (e.g., cat) category representations from perceptual input. To test the predicted global‐to‐basic order of category learning of the network, 2‐month‐olds were administered the familiarization/novelty‐preference procedure and examined for representation of global and basic‐level categories. Infants formed a global category representation for mammals that excluded furniture but not a basic‐level representation for cats that excluded elephants, rabbits, or dogs. The empirical results are consistent with the global‐to‐basic learning sequence observed in the network simulations.     

Young Infants' Performance in the Object‐Variation Version of the Above‐Below Categorization Task: A Result of Perceptual Distraction or Conceptual Limitation?

Five experiments were conducted to examine the performance of young infants on above versus below categorization tasks. Experiments 1 and 2 showed that infants did not form abstract categorical representations for above and below when familiarized with different objects depicted in a constant spatial relation relative to a horizontal bar and tested on a novel object depicted in the familiar and novel spatial relation. Experiments 3 through 5 examined perceptual‐attentional distraction versus conceptually based generalization explanations for young infant performance in the object‐variation version of the above‐below categorization task. Experiments 3 and 4 demonstrated that infants still did not form abstract categorical representations for above and below when object variation was removed from the familiarization trials or when object novelty was reduced during the preference test trials. However, Experiment 5 showed that 3‐ and 4‐month‐olds succeeded on the above versus below categorization task when familiarized with object variation and preference tested with a familiar versus novel object‐bar relation. These results indicate that young infants can form categorical representations for above and below in the object‐variation version of the above‐below categorization task, but that such representations are specific to the particular objects presented. Young infant performance in the object‐variation version of the above‐below categorization task thus reflects a conceptually based generalization limit rather than a problem of perceptual‐attentional distraction.     

One is Not Enough: Multiple Exemplars Facilitate Infants' Generalizations of Novel Properties

Across three experiments, we examined 9‐ and 11‐month‐olds' mappings of novel sound properties to novel animal categories. Infants were familiarized with novel animal–novel sound pairings (e.g., Animal A [red]–Sound 1) and then tested on: (1) their acquisition of the original pairing and (2) their generalization of the sound property to a new member of a familiarized category (e.g., Animal A [blue]–Sound 1). When familiarized with a single exemplar of a category, 11‐month‐olds showed no evidence of acquiring or generalizing the animal–sound pairings. In contrast, 11‐month‐olds learnt the original animal–sound mappings and generalized the sound property to a novel member of that category when familiarized with multiple exemplars of a category. Finally, when familiarized with multiple exemplars, 9‐month‐old infants learnt the original animal–sound pairing, but did not extend the novel sound property. The results of these experiments provide evidence for developmental differences in the facilitative role of multiple exemplars in promoting the learning and generalization of information.     

5‐Month‐Olds’ Categorization of Novel Objects: Task and Measure Dependence

To examine key parameters of the initial conditions in early category learning, two studies compared 5‐month‐olds’ object categorization between tasks involving previously unseen novel objects, and between measures within tasks. Infants in Experiment 1 participated in a visual familiarization–novelty preference (VFNP) task with two‐dimensional (2D) stimulus images. Infants provided no evidence of categorization by either their looking or their examining even though infants in previous research systematically categorized the same objects by examining when they could handle them directly. Infants in Experiment 2 participated in a VFNP task with 3D stimulus objects that allowed visual examination of objects’ 3D instantiation while denying manual contact with the objects. Under these conditions, infants demonstrated categorization by examining but not by looking. Focused examination appears to be a key component of young infants’ ability to form category representations of novel objects, and 3D instantiation appears to better engage such examining.     

A Comparison of Visual Familiarization and Object‐Examining Measures of Categorization in 9‐Month‐Old Infants

Three studies were conducted to determine whether differential patterns of categorization observed in studies using visual familiarization and object‐examining measures hold up as procedural confounds are eliminated. In Experiment 1, we attempted as direct a comparison as possible between visual and object‐examining measures of categorization. Consistent with previous reports, 9‐month‐old infants distinguished a basic‐level contrast (dog–horse) in the visual task, but not in the examining task. Experiment 2 was designed to reduce levels of nonexploratory activity in an examining task; 9‐month‐olds again failed to distinguish categories of dogs and horses. In Experiment 3, we adopted a paired‐comparison test format in the object‐examining task. Infants did display a novel category preference under paired testing conditions. The results suggest that the different patterns of categorization often seen in looking and touching tasks are a reflection, not of different categorization processes, but of the differential sensitivity of the tasks.     

The Role of Context in the Categorization of Hybrid Toy Stimuli by 18‐Month‐Olds

Using a sequential touching procedure, we examined whether 18‐month‐olds could use different categorization strategies adaptively as a function of context. Infants were presented with test toys of land animals (quadrupeds), cars, and hybrids made by recombining car parts with animal parts. Infants who experienced a context emphasizing a taxonomic divide were subsequently more likely to form categories that reflected a taxonomic divide, whereas infants who experienced a context emphasizing a partonomic divide were subsequently more likely to form categories based on functional parts. These results suggest that 18‐month‐olds can adapt their categorization strategies flexibly in accordance with ambient contextual cues. This adds to the growing body of evidence that early categorization is flexible and not rigidly tied to characteristic features in the environment.     

Relating 7‐Month‐Olds Visuo‐Spatial Working Memory to Other Basic Mental Skills Assessed With Two Different Versions of the Habituation–Dishabituation Paradigm

This study examines the relationship between various basic mental processing abilities in infancy. Two groups of 7‐month‐olds received the same delayed‐response task to assess visuo‐spatial working memory, but two different habituation–dishabituation tasks to assess processing speed and recognition memory. The single‐stimulus group (N = 32) was familiarized with only one abstract stimulus, whereas the categorization group (N = 32) received varying exemplars of the same kind. In the categorization group, infants high on working memory showed stronger habituation and dishabituation responses than infants scoring low in working memory. No corresponding relations were found for the single‐stimulus group. This suggests that working memory performance is systematically linked to other basic mental skills in 7‐month‐olds, but that corresponding relations may not get evident in any kind of habituation–dishabituation procedure. Implications for understanding the complex interplay of basic mental abilities in infancy will be discussed.     

Six‐Month‐Olds' Detection of Clauses Embedded in Continuous Speech: Effects of Prosodic Well‐Formedness

Three experiments investigated the role of prosodic structure for infants' recognition of embedded word sequences. Six‐month‐olds were familiarized with 2 versions of the same sequence, 1 corresponding to a well‐formed prosodic unit and the other to a prosodically ill‐formed sequence (although a successive word series). Next, infants heard 2 test passages. One included the well‐formed unit, and the other included the ill‐formed sequence. In Experiment 1, infants listened longer to the passage containing the well‐formed unit, suggesting that such units, even when they are embedded, are better recognized. Experiments 2 and 3 showed that this better recognition does not depend on an acoustic match between the familiarized sequences and their later embeddings. This suggests that the advantage of the well‐formed unit is at least partially due to infants' use of prosody to parse continuous speech.     

Mechanisms of Categorization in Infancy

This article presents a connectionist model of correlation‐based categorization by 10‐month‐old infants (Younger, 1985). Simple autoencoder networks were exposed to the same stimuli used to test 10‐month‐olds. The familiarization regime was kept as close as possible to that used with the infants. The performance of the model matched that of the infants. Both infants and networks used covariation information (when available) to segregate items into separate categories. The model provides a mechanistic account of category learning within a test session. It demonstrates how categorization arises as the product of an inextricable interaction between the subject (the infant) and the environment (the stimuli). The computational characteristics of both subject and environment must be considered in conjunction to understand the observed behaviors.     

A Comparison of Infants' Categorization in Paired and Successive Presentation Familiarization Tasks

Three experiments directly compared infants' categorization in variations of the visual familiarization task. In each experiment, 4‐ or 6‐month‐old infants were familiarized with a collection of dogs or cats and then their response to novel dogs and cats was assessed. In Experiment 1, 4‐month‐old infants responded to the exclusive distinction of dogs or cats when tested in a paired‐comparison task. In Experiments 2 and 3, 6‐month‐old infants, but not 4‐month‐old infants, responded to this same distinction in a successive presentation task, even when the amount of familiarization was equated to that of the paired comparison task. Therefore, familiarization with a particular set of stimuli does not induce infants to respond to a single category but rather they respond to different categories depending on features of the task.     

Integrated Emotion Processing in Infancy: Matching of Faces and Bodies

Accurate assessment of emotion requires the coordination of information from different sources such as faces, bodies, and voices. Adults readily integrate facial and bodily emotions. However, not much is known about the developmental origin of this capacity. Using a familiarization paired‐comparison procedure, 6.5‐month‐olds in the current experiments were familiarized to happy, angry, or sad emotions in faces or bodies and tested with the opposite image type portraying the familiar emotion paired with a novel emotion. Infants looked longer at the familiar emotion across faces and bodies (except when familiarized to angry images and tested on the happy/angry contrast). This matching occurred not only for emotions from different affective categories (happy, angry) but also within the negative affective category (angry, sad). Thus, 6.5‐month‐olds, like adults, integrate emotions from bodies and faces in a fairly sophisticated manner, suggesting rapid development of emotion processing early in life.     

Successful Word Recognition by 10‐Month‐Olds Given Continuous Speech Both at Initial Exposure and Test

Most words that infants hear occur within fluent speech. To compile a vocabulary, infants therefore need to segment words from speech contexts. This study is the first to investigate whether infants (here: 10‐month‐olds) can recognize words when both initial exposure and test presentation are in continuous speech. Electrophysiological evidence attests that this indeed occurs: An increased extended negativity (word recognition effect) appears for familiarized target words relative to control words. This response proved constant at the individual level: Only infants who showed this negativity at test had shown such a response, within six repetitions after first occurrence, during familiarization.     

From Syllables to Syntax: Multilevel Statistical Learning by 12‐Month‐Old Infants

To successfully acquire language, infants must be able to track multiple levels of regularities in the input. In many cases, regularities only emerge after some learning has already occurred. For example, the grammatical relationships between words are only evident once the words have been segmented from continuous speech. To ask whether infants can engage in this type of learning process, 12‐month‐old infants in 2 experiments were familiarized with multiword utterances synthesized as continuous speech. The words in the utterances were ordered based on a simple finite‐state grammar. Following exposure, infants were tested on novel grammatical and ungrammatical sentences. The results indicate that the infants were able to perform 2 statistical learning tasks in sequence: first segmenting the words from continuous speech, and subsequently discovering the permissible orderings of the words. Given a single set of input, infants were able to acquire multiple levels of structure, suggesting that multiple levels of representation (initially syllable‐level combinations, subsequently word‐level combinations) can emerge during the course of learning.     

Six‐Month‐Olds Comprehend Words That Refer to Parts of the Body

Comprehending spoken words requires a lexicon of sound patterns and knowledge of their referents in the world. Tincoff and Jusczyk (1999) demonstrated that 6‐month‐olds link the sound patterns “Mommy” and “Daddy” to video images of their parents, but not to other adults. This finding suggests that comprehension emerges at this young age and might take the form of very specific word‐world links, as in “Mommy” referring only to the infant’s mother and “Daddy” referring only to the infant’s father. The current study was designed to investigate if 6‐month‐olds also show evidence of comprehending words that can refer to categories of objects. The results show that 6‐month‐olds link the sound patterns “hand” and “feet” to videos of an adult’s hand and feet. This finding suggests that very early comprehension has a capacity beyond specific, one‐to‐one, associations. Future research will need to consider how developing categorization abilities, social experiences, and parent word use influence the beginnings of word comprehension.     

Bias for Vocalic Over Consonantal Information in 6‐Month‐Olds

Human languages rely on the ability to learn and produce an indefinite number of words by combining consonants and vowels in a lawful manner. The categorization of speech representations into consonants and vowels is evidenced by the tendency of adult speakers, attested in many languages, to use consonants and vowels for different tasks. Consonants are favored in lexical tasks, while vowels are favored to learn structural regularities. Recent results suggest that this specialization is already observable at 12 months of age in Italian participants. Here, we investigated the representations of younger infants. In a series of anticipatory looking experiments, we showed that Italian 6‐month‐olds rely more on vowels than on consonants when learning the predictions made by individual words (Experiment 1) and are better at generalizing a structure when it is implemented over vowels than when it is implemented over consonants (Experiments 2 and 3). Until 6 months of age, infants thus show a general vocalic bias, which contrasts with the specialization previously observed at 12 months. These results suggest the format of speech representations changes during the second semester of life.     

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.     

Mechanisms of Visual Object Recognition in Infancy: Five‐Month‐Olds Generalize Beyond the Interpolation of Familiar Views

This work examined predictions of the interpolation of familiar views (IFV) account of object recognition performance in 5‐month‐olds. Infants were familiarized to an object either from a single viewpoint or from multiple viewpoints varying in rotation around a single axis. Object recognition was then tested in both conditions with the same object rotated around a novel axis. Infants in the multiple‐views condition recognized the object, whereas infants in the single‐view condition provided no evidence for recognition. Under the same 2 familiarization conditions, infants in a 2nd experiment treated as novel an object that differed in only 1 component from the familiar object. Infants' object recognition is enhanced by experience with multiple views, even when that experience is around an orthogonal axis of rotation, and infants are sensitive to even subtle shape differences between components of similar objects. In general, infants' performance does not accord with the predictions of the IFV model of object recognition. These findings motivate the extension of future research and theory beyond the limits of strictly interpolative mechanisms.     

Infants' First Words are not Phonetically Specified: Own Name Recognition in British English‐Learning 5‐Month‐Olds

By the end of their first year of life, infants’ representations of familiar words contain phonetic detail; yet little is known about the nature of these representations at the very beginning of word learning. Bouchon et al. ( 2015 ) showed that French‐learning 5‐month‐olds could detect a vowel change in their own name and not a consonant change, but also that infants reacted to the acoustic distance between vowels. Here, we tested British English‐learning 5‐month‐olds in a similar study to examine whether the acoustic/phonological characteristics of the native language shape the nature of the acoustic/phonetic cues that infants pay attention to. In the first experiment, British English‐learning infants failed to recognize their own name compared to a mispronunciation of initial consonant (e.g., Molly versus Nolly) or vowel (e.g., April versus Ipril). Yet in the second experiment, they did so when the contrasted name was phonetically dissimilar (e.g., Sophie versus Amber). Differences in phoneme category (stops versus continuants) between the correct consonant versus the incorrect one significantly predicted infants’ own name recognition in the first experiment. Altogether, these data suggest that infants might enter into a phonetic mode of processing through different paths depending on the acoustic characteristics of their native language.     

Getting into the Groove: The Development of Tempo‐Flexibility Between 10 and 18 Months of Age

Despite good early rhythm processing abilities, and clear enjoyment of music, infants appear not to be able to spontaneously synchronize their movement to the beat of a song (Zentner and Eerola, Proceedings of the National Academy of Sciences, 107, 2010, 5768). We present a new social bell‐ringing task designed to facilitate synchronous movement to music in infants. Ten‐month‐olds, 18‐month‐olds, and adults were played musical tracks of various tempos and given handheld bells to ring, in the presence of either a live experimenter or an animated nonsocial stimulus. Surface electromyography (EMG) was used to measure the timing of arm movements during periods of bell ringing. Infants showed no evidence of synchronous bell ringing at any tempo. However, while the 10‐month‐olds did not modulate their ringing to the music tempo, the 18‐month‐olds showed tempo‐flexibility. Moreover, 18‐month‐olds displayed more associated behaviors such as bouncing and rocking in the absence (rather than presence) of a social partner, whereas the behavior of the 10‐month‐olds was not modulated by the presence or absence of a social partner. The results suggest a distinction between “moving together” and “moving to the beat,” which may have separate underlying mechanisms and developmental trajectories.