2018 Alternates 6406

2018 Alternates | Saturday, November 3, 2018 | Poster Session II, Metcalf Small | 3:15pm

Enhancement of stop contrast or emergence of new targets?: Implications on language development in Japanese
H. Hwang, R. Mazuka, M. Takada

Infants must acquire the ability to discriminate contrastive sounds in a language. If the input for infants involves ongoing sound changes, one of the challenges infants encounter can be varying cues across generations. Interestingly, a change-in-progress of laryngeal contrasts is reported in Japanese voiced stops; the lack of pre-voicing is observed frequently among younger speakers (Takada 2011). It raises an interesting question whether this change is reflected in maternal input, or mothers still exhibit pre-voicing prevalently when they talk to their infants to enhance the laryngeal contrast. What are the implications of the changes if infants’ speech development is closely linked to sound changes in the maternal input?

A corpus of spontaneous Japanese was analyzed. The RIKEN Japanese Mother-Infant Conversation Corpus consists of infant-directed speech (IDS) and adult-directed speech (ADS) by 22 mothers. Voice onset time (VOT) was measured for stops in the initial position of Intonational Phrase preceded by a pause longer than 200ms. Moreover, careful/read speech from the same speakers was also analyzed which enabled us to directly compare it and spontaneous speech.

As shown in Figure 1, the measurements reveal that the VOT distribution between voiced and voiceless stops is not different in IDS, suggesting no facilitative function of IDS. Regardless of register, approximately 20% of voiced stops are pre-voiced in spontaneous speech. In careful/reading speech, on the other hand, nearly all the voiced stops show positive VOT, implying that the VOT target of voiced stops in Japanese has changed at least for female speakers of this age group. Also, the quite adjacent distribution of two stop categories indicates difficulties in discriminating the voicing contrast.

It has been widely believed that sensitivity to stop VOT appears relatively early, and English- learning infants are capable of discriminating native stop contrasts before 6 months (Burns et al. 2007). Yet, early development of laryngeal contrast in Japanese has not been studied, which leads us to the second question: Can Japanese-learning infants perceive their native stop contrast as early as English-learning infants?

The visual habituation method was utilized to test Japanese-learning infants aged 5 and 9 monts-old. Averaged looking times of each age group are shown in Figure 2(a). Paired t-tests reveal that both age groups do not yield significantly different looking times between the same and switch trials. It seems that the discriminability of the Japanese voicing contrast is acquired later in the perceptual development. This “later” discrimination in Japanese can be attributed to the input; the voicing contrast in the initial position was not salient enough. Thus stops in intervocalic position (/ebe/-/epe/) were further tested, where [b] was fully voiced. The results shown in Figure 2(b) support that perceptual cues in intervocalic stops are rich enough for 5-month-olds to discriminate the contrast.

The results of the behavioral study confirm that the development of Japanese voicing perception is acquired relatively late, highlighting the weak discriminability of stop contrast due to the ongoing sound change in maternal input.

References

Burns, T.C., Yoshika, K.A., Hill, K., & Werker, J.F. (2007). The development of phonetic representation in bilingual and monolingual infants. Applied Psycholinguistics, 28, 455- 474.

Takada, M. (2011) Nihongo no goto heisaon no kenkyu: VOT no kyojiteki bunpu totsujiteki henka [Research on the word-initial stops of Japanese: Synchronic distribution and diachronic change in VOT]. Tokyo: Kurosio.