Shigeaki Amano

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.

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.

A method for fundamental frequency estimation and voicing decision: Application to infant utterances recorded in real acoustical environments

This paper proposes a method for fundamental frequency (F0) estimation and voicing decision that can handle wide-ranging speech signals including adult and infant utterances recorded in real noisy environments. In particular, infant utterances have unique characteristics that are different from those of adults, such as a wide F0 range, F0 abrupt transitions, and unique energy distribution patterns over frequencies. Therefore, conventional methods that were developed mainly for adult utterances do not necessarily work well for infant utterances especially when the signals are contaminated by background noise. Several techniques are introduced into the proposed method to cope with this problem. We show that the ripple-enhanced power spectrum based method (REPS) can estimate the F0s robustly, and that the use of instantaneous frequency (IF) enables us to refine the accuracy of the F0 estimates. In addition, the degree of dominance defined based on the IF is introduced as a robust voicing decision measure. The effectiveness of the proposed method is confirmed in terms of gross pitch errors and voicing decision errors in comparison with the recently proposed methods, Praat and YIN, using both longitudinal recordings of Japanese infant utterances and adult utterances.

Modality dependency of familiarity ratings of Japanese words

Familiarity ratings for a large number of aurally and visually presented Japanese words were measured for 11 subjects, in order to investigate the modality dependency of familiarity. The correlation coefficient between auditory and visual ratings was .808, which is lower than that observed for English words, suggesting that a substantial portion of the mental lexicon is modality dependent. It was shown that the modality dependency is greater for low-familiarity words than it is for medium- or high-familiarity words. This difference between the low- and the medium- or high-familiarity words has a relationship to orthography. That is, the dependency is larger in words consisting only ofkanji, which may have multiple pronunciations and usually represent meaning, than it is in words consisting only ofhiragana or katakana, which have a single pronunciation and usually do not represent meaning. These results indicate that the idiosyncratic characteristics of Japanese orthography contribute to the modality dependency.

Longitudinal developmental changes in spectral peaks of vowels produced by Japanese infants.

This paper describes a longitudinal analysis of the vowel development of two Japanese infants in terms of spectral resonant peaks. This study aims to investigate when and how the two infants become able to produce categorically separated vowels, and covers the ages of 4 to 60 months in order to provide detailed findings on the developmental process of speech production. The two lower spectral peaks were estimated from vowels extracted from natural spontaneous speech produced by the infants. Phoneme labeled and transcription-independent unlabeled data analyses were conducted. The labeled data analysis revealed longitudinal trends in the developmental change, which correspond to the articulation positions of the tongue and the rapid enlargement of the articulatory organs. In addition, the distribution of the two spectral peaks demonstrates the vowel space expansion that occurs with age. An unlabeled data analysis technique derived from the linear discriminant analysis method was introduced to measure the vowel space expansion quantitatively. It revealed that the infants vowel space becomes similar to that of an adult in the early stages. In terms of both labeled and unlabeled properties, these results suggested that infants become capable of producing categorically separated vowels by 24 months.

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.

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.

Development of Japanese infant speech database from longitudinal recordings

Developmental research on speech production requires both a cross-sectional and a longitudinal speech database. Previous longitudinal speech databases are limited in terms of recording period or number of utterances. An infant speech database was developed from 5 years of recordings containing a large number of daily life utterances of five Japanese infants and their parents. The resulting database contains 269,467 utterances with various types of information including a transcription, an F0 value, and a phoneme label. This database can be used in future research on the development of speech production.

Relationships Between Depression and Stress Factors in Housework and Paid Work Among Japanese Women

Objective/Background The prevalence of depression in women is two times as much as that in men. However, the rehabilitation programme for return to work for patients with depression in Japan mainly focuses on male individuals. Japanese working women usually have the central role in housework in addition to paid work. Therefore, we hypothesized that Japanese working women with depression need a support programme for housework as well as paid work. The purpose of this study was to investigate the stress factors relevant to the existence of depression, in both paid work and housework, among working women. Methods This study recruited 35 women with depression and 35 women without depression. We carried out a cross-sectional investigation with two questionnaires having the same structure: The National Institute for Occupational Safety and Health (NIOSH) Generic Job Stress Questionnaire (for paid work) and the NIOSH Generic Housekeeping Labor Stress Questionnaire (for housework). We extracted the stress factors contributing to the existence of depression using logistic regression. Results Three stress factors were found–-two in housework, and one in paid work. In housework, variance in workload and underutilization of abilities were associated with the presence of depression. In paid work, interpersonal conflict was an associated factor. Conclusion Rehabilitation programmes involving variance in workload and under self-evaluation in housework, and interpersonal conflict in paid work must be adequately addressed to support working women with depression.

Production of single and geminate stops in Japanese three- and four-mora wordsa)

This study examined the durational structure of single and geminate stop distinction produced in three- and four-mora words of Japanese, (C(1))V(1)(C(2))C(2)V(2)X [(C(2))C(2) = the contrasting consonants; X = a CV mora, the moraic nasal, or a long vowel as part of V(2)]. The questions addressed were how factors such as speaking rate, segmental variability, and moraic composition of words affected the stop quantity distinction in words longer than well-studied disyllabic words, and whether there exists an invariant parameter that classified these two stop categories. Results showed that all of those factors systematically affected the duration of the contrasting stop closure, the unit of [(C(1))V(1)(C(2))C(2)V(2)], and the entire three- and four-mora words. However, the durational units of moras and words were well-structured, and the ratio of the contrasting stop closure to the [(C(1))V(1)(C(2))C(2)V(2)] unit, as well as the ratio of the closure to the entire word, were found to be invariant in indicating the stop quantity distinction. These results support the theory of relational acoustic invariance [Pickett et al., Phonetica 56, 135-157 (1999)] on the part of production. Furthermore, the results provide insight into different versions of Japanese mora hypothesis [Han, The Study of Sounds 10, 65-80 (1962); Port et al., J. Acoust. Soc. Am. 81(5), 1574-1585 (1987)], which have been under debate for five decades.