The majority of infants with permanent congenital hearing loss fall significantly behind their normal hearing peers in the development of receptive and expressive oral communication skills. Independent of any prosthetic intervention for infants with hearing loss, the social and linguistic environment can still be optimal or sub-optimal and so can exert significant positive or negative effects on speech and language acquisition, with far-reaching beneficial or adverse effects, respectively. This study focuses on the nature of the linguistic environment of infants with hearing loss, in particular speech directed to infants (infant-directed speech, IDS). The first experiment used a cross-sectional design that assessed the acoustic features in IDS to infants with HL with a specific focus on how infants’ chronological age and hearing experience may affect these features. The second experiment included a longitudinal investigation focusing on the acoustic features of IDS to infants with HL and infants with NH of the same amount of hearing experience. The results demonstrate that mothers adjust their speech to infants with HL in a similar manner as in IDS to infants with normal hearing. However, some differences exist.
The second part of the talk will present the project on the role of infants’ home speech environment in language development during the first two years of life. This project examined the composition of early infants’ speech environment and its effects on infants’ language outcomes by using a unique dataset of large-scale naturalistic Japanese mother-infant dyads obtained in home settings. Specifically, we focused on the quantity of speech input, contingent vocal responsiveness in mother-infant interactions, and language milestones such as perceptual attunement and receptive and expressive vocabulary skills. The preliminary results demonstrate that Japanese infants from high SES background receive a similar amount of speech input as do infants from high SES North American families. Furthermore, the results indicate the relation between speech perception during the 1st year and vocabulary development during the 2nd year of life.
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