Task-appropriate input supports word-object association in 14-month-old female infants.

Fourteen-month-old infants are unable to link minimal pair nonsense words with novel objects (Stager & Werker, 1997). Might an adult's productions in a word learning context support minimal pair word-object association in these infants? We recorded a mother interacting with her 24-month-old son, and with her 5-month-old son, producing nonsense words bin and din. We used these productions to determine if they had a differential effect on 14-month-old infants' word-object association abilities. Females hearing the words spoken to the older infant, but not those to the younger, succeeded. We suggest that the task-appropriateness of utterances can support infant word learning.

The Use of Pitch Accent in Word-Object Association by Monolingual Japanese Infants.

This study investigated the lexical use of Japanese pitch accent in Japanese-learning infants. A word-object association task revealed that 18-month-old infants succeeded in learning the associations between two nonsense objects paired with two nonsense words minimally distinguished by pitch pattern (Experiment 1). In contrast, 14-month-old infants failed (Experiment 2). Eighteen-month-old infants succeeded even for sounds that contained only the prosodic information (Experiment 3). However, a subsequent experiment revealed that 14-month-old infants succeeded in an easier single word-object task using pitch contrast (Experiment 4). These findings indicate that pitch pattern information is robustly available to 18-month-old Japanese monolingual infants in a minimal pair word-learning situation, but only partially accessible in the same context for 14-month-old infants.

The Role of Auditory and Visual Speech in Word Learning at 18 Months and in Adulthood.

Visual information influences speech perception in both infants and adults. It is still unknown whether lexical representations are multisensory. To address this question, we exposed 18-month-old infants (n = 32) and adults (n = 32) to new word-object pairings: Participants either heard the acoustic form of the words or saw the talking face in silence. They were then tested on recognition in the same or the other modality. Both 18-month-old infants and adults learned the lexical mappings when the words were presented auditorily and recognized the mapping at test when the word was presented in either modality, but only adults learned new words in a visual-only presentation. These results suggest developmental changes in the sensory format of lexical representations.

Infants track word forms in early word-object associations.

A central component of language development is word learning. One characterization of this process is that language learners discover objects and then look for word forms to associate with these objects (Mcnamara, 1984; Smith, 2000). Another possibility is that word forms themselves are also important, such that once learned, hearing a familiar word form will lead young word learners to look for an object to associate with it (Juscyzk, 1997). This research investigates the relative weighing of word forms and objects in early word-object associations using the anticipatory eye-movement paradigm (AEM; McMurray & Aslin, 2004). Eighteen-month-old infants and adults were taught novel word-object associations and then tested on ambiguous stimuli that pitted word forms and objects against each other. Results revealed a change in weighing of these components across development. For 18-month-old infants, word forms weighed more in early word-object associative learning, while for adults, objects were more salient. Our results suggest that infants preferentially use word forms to guide the process of word-object association.

Perceptual narrowing of linguistic sign occurs in the 1st year of life.

Over their 1st year of life, infants'"universal" perception of the sounds of language narrows to encompass only those contrasts made in their native language (J. F. Werker & R. C. Tees, 1984). This research tested 40 infants in an eyetracking paradigm and showed that this pattern also holds for infants exposed to seen language-American Sign Language (ASL). Four-month-old, English-only, hearing infants discriminated an ASL handshape distinction, while 14-month-old hearing infants did not. Fourteen-month-old ASL-learning infants, however, did discriminate the handshape distinction, suggesting that, as in heard language, exposure to seen language is required for maintenance of visual language discrimination. Perceptual narrowing appears to be a ubiquitous learning mechanism that contributes to language acquisition.

Now you hear it, now you don't: vowel devoicing in Japanese infant-directed speech.

In this work, we examine a context in which a conflict arises between two roles that infant-directed speech (IDS) plays: making language structure salient and modeling the adult form of a language. Vowel devoicing in fluent adult Japanese creates violations of the canonical Japanese consonant-vowel word structure pattern by systematically devoicing particular vowels, yielding surface consonant clusters. We measured vowel devoicing rates in a corpus of infant- and adult-directed Japanese speech, for both read and spontaneous speech, and found that the mothers in our study preserve the fluent adult form of the language and mask underlying phonological structure by devoicing vowels in infant-directed speech at virtually the same rates as those for adult-directed speech. The results highlight the complex interrelationships among the modifications to adult speech that comprise infant-directed speech, and that form the input from which infants begin to build the eventual mature form of their native language.

Perception of vowel length by Japanese- and English-learning infants.

This study investigated vowel length discrimination in infants from 2 language backgrounds, Japanese and English, in which vowel length is either phonemic or nonphonemic. Experiment 1 revealed that English 18-month-olds discriminate short and long vowels although vowel length is not phonemically contrastive in English. Experiments 2 and 3 revealed that Japanese 18-month-olds also discriminate the pairs but in an asymmetric manner: They detected only the change from long to short vowel, but not the change in the opposite direction, although English infants in Experiment 1 detected the change in both directions. Experiment 4 tested Japanese 10-month-olds and revealed a symmetric pattern of discrimination similar to that of English 18-month-olds. Experiment 5 revealed that native adult Japanese speakers, unlike Japanese 18-month-old infants who are presumably still developing phonological perception, ultimately acquire a symmetrical discrimination pattern for the vowel contrasts. Taken together, our findings suggest that English 18-month-olds and Japanese 10-month-olds perceive vowel length using simple acoustic?phonetic cues, whereas Japanese 18-month-olds perceive it under the influence of the emerging native phonology, which leads to a transient asymmetric pattern in perception.

Infant Discrimination of a Morphologically Relevant Word-Final Contrast.

Six-, 12-, and 18-month-old English-hearing infants were tested on their ability to discriminate nonword forms ending in the final stop consonants /k/ and /t/ from their counterparts with final /s/ added, resulting in final clusters /ks/ and /ts/, in a habituation-dishabituation, looking time paradigm. Infants at all 3 ages demonstrated an ability to discriminate this type of contrast, a contrast that constitutes one phonetic cue for the English morphological concepts of plural, possession, and person. These results suggest that across a significant portion of the development of infants' speech perception, this type of final contrast is discriminable.

Age-related changes in sensitivity to native phonotactics in Japanese infants.

Japanese infants at the ages of 6, 12, and 18 months were tested on their ability to discriminate three nonsense words with different phonotactic status: canonical keetsu, noncanonical but possible keets, and noncanonical and impossible keet. The results showed that 12 and 18 months olds discriminate the keets/keetsu pair, but infants in all age groups fail to discriminate the keets/keet pair. Taken together with the findings in our previous study [Kajikawa et al., J. Acoust. Soc. Am. 120(4), 2278-2284 (2006)], these results suggest that Japanese infants develop the perceptual sensitivity for native phonotactics after 6 months of age, and that this sensitivity is limited to canonical patterns at this early developmental stage.

Infant-directed speech supports phonetic category learning in English and Japanese.

Across the first year of life, infants show decreased sensitivity to phonetic differences not used in the native language [Werker, J. F., & Tees, R. C. (1984). Cross-language speech perception: evidence for perceptual reorganization during the first year of life. Infant Behaviour and Development, 7, 49-63]. In an artificial language learning manipulation, Maye, Werker, and Gerken [Maye, J., Werker, J. F., & Gerken, L. (2002). Infant sensitivity to distributional information can affect phonetic discrimination. Cognition, 82(3), B101-B111] found that infants change their speech sound categories as a function of the distributional properties of the input. For such a distributional learning mechanism to be functional, however, it is essential that the input speech contain distributional cues to support such perceptual learning. To test this, we recorded Japanese and English mothers teaching words to their infants. Acoustic analyses revealed language-specific differences in the distributions of the cues used by mothers (or cues present in the input) to distinguish the vowels. The robust availability of these cues in maternal speech adds support to the hypothesis that distributional learning is an important mechanism whereby infants establish native language phonetic categories.

Cross-language sensitivity to phonotactic patterns in infants.

This study explored sensitivity to word-level phonotactic patterns in English and Japanese monolingual infants. Infants at the ages of 6, 12, and 18 months were tested on their ability to discriminate between test words using a habituation-switch experimental paradigm. All of the test words, neek, neeks, and neekusu, are phonotactically legitimate for English, whereas the first two words are critically noncanonical in Japanese. The language-specific phonotactical congruence influenced infants' performance in discrimination. English-learning infants could discriminate between neek and neeks at the age of 18 months, but Japanese infants could not. There was a similar developmental pattern for infants of both language groups for discrimination of neek and neeks, but Japanese infants showed a different trajectory from English infants for neekusu/neeks. These differences reflect the different status of these word patterns with respect to the phonotactics of both languages, and reveal early sensitivity to subtle phonotactic and language input patterns in each language.

Japanese listeners' perceptions of phonotactic violations.

The canonical form for Japanese words is (Consonant)Vowel(Consonant) Vowel-. However, a regular process of high vowel devoicing between voiceless consonants and word-finally after voiceless consonants results in consonant clusters and word-final consonants, apparent violations of that phonotactic pattern. We investigated Japanese adults' perceptions of these violations, asking them to rate both canonical and noncanonical nonsense forms on a scale of goodness. Results indicate that adults show evidence of being guided in making their judgments by an implicit understanding of both typical canonical forms and appropriate contexts for vowel devoicing.