Acoustic correlates of allophonic versus phonemic dimensions in monolingual and bilingual infants' input

• Acoustic cues to phonological status were studied in French and English.
• Monolingual and bilingual infant-directed vowels were elicited in a crossed design.
• As predicted, effect sizes for vowel tenseness were greater in English than in French.
• As predicted, effect sizes for vowel nasality were greater in French than in English.
• However, cues to phonological status were significant only for tenseness.

Allophones are diverse phonetic instantiations of a single underlying sound category. As such, they pose a peculiar problem for infant language learners: These variants occur in the ambient language, but they are not used to encode lexical contrasts. Infants' sensitivity to sounds varying along allophonic dimensions declines by 11 months of age, suggesting that there must be information to phonological status available to pre-lexical infants. The present work tests one specific type of information: acoustic implementation. It was hypothesized that the acoustic distance between two vowel categories is smaller when the dimension along which the two vowels differ is allophonic (e.g., vowel nasality in American English, vowel tenseness in Quebec French) compared to when it is phonemic (e.g., vowel tenseness in American English, vowel nasality in Quebec French). Monolingual mothers speaking either English or French and bilingual mothers speaking both languages were recorded while they described objects to their 11-month-olds. Results provided weak support for the main hypothesis.