Maternal interactions with a hearing and hearing-imparied twin : similarities and differences in speech input, interaction quality, and word production

This study examined a mother’s speech style and interactive behaviors with her twin sons: 1 with bilateral hearing impairment (HI) and the other with normal hearing (NH). The mother was video-recorded interacting with her twin sons when the boys were 12.5 and 22 months of age. Mean F0, F0 range, duration, and F1/F2 vowel space of the corner vowels /i/, /u/, and /a/ were compared in her infant-directed (ID) and adult-directed (AD) speech. The interactions were also coded for emotional availability, and vocabulary size was collected at 17 and 22 months. Acoustic analyses revealed no difference among mean F0, F0 range, and duration between the twins. In contrast, when the corner vowels were plotted in F1/F2 vowel space, the results showed a diminished vowel space in speech to the HI twin compared to the NH twin. Ratings of emotional availability were lower for the HI than the NH twin, but the HI twin had a larger expressive vocabulary on both occasions, albeit in the lower percentile. The mother appears more focused on maintaining the attention of the HI infant using the typical ID exaggerations to prosody and overlooking linguistic features such as the hyperarticulation of her vowels. The results have implications for early intervention strategies.