Mommy, speak clearly: induced hearing loss shapes vowel hyperarticulation.

Talkers hyperarticulate vowels when communicating with listeners that require increased speech intelligibility. Vowel hyperarticulation is said to be motivated by knowledge of the listener's linguistic needs because it typically occurs in speech to infants, foreigners and hearing-impaired listeners, but not to non-verbal pets. However, the degree to which vowel hyperarticulation is determined by feedback from the listener is surprisingly less well understood. This study examines whether mothers' speech input is driven by knowledge of the infant's linguistic competence, or by the infant's feedback cues. Specifically, we manipulated (i) mothers' knowledge of whether they believed their infants could hear them or not, and (ii) the audibility of the speech signal available to the infant (full or partial audibility, or inaudible). Remarkably, vowel hyperarticulation was completely unaffected by mothers' knowledge; instead, there was a reduction in the degree of hyperarticulation such that vowels were hyperarticulated to the greatest extent in the full audibility condition, there was reduced hyperarticulation in the partially audible condition, and no hyperarticulation in the inaudible condition. Thus, while it might be considered adaptive to hyperarticulate speech to the hearing-impaired adult or infant, when these two factors (infant and hearing difficulty) are coupled, vowel hyperarticulation is sacrificed. Our results imply that infant feedback drives talker behavior and raise implications for intervention strategies used with carers of hearing-impaired infants.