The phonetic landscape in infant consonant perception is an uneven terrain

Previous research revealing universal biases in infant vowel perception forms the basis of the Natural Referent Vowel (NRV) framework (Polka & Bohn, 2011). To explore the feasibility of extending this framework to consonant manner perception, we investigated perception of the stop vs. fricative consonant contrast /b/-/v/ to test the hypothesis that young infants will display a perceptual bias grounded in the acoustic-phonetic properties of these sounds. We examined perception of stop-initial /bas/ and fricative-initial /vas/ syllables in English-learning and French-learning 5- to 6-month-olds. The /b/ and /v/ sounds distinguish words in English and French but have different distributional patterns; in spoken English /b/ occurs more frequently than /v/ whereas in spoken French /v/ occurs more frequently than /b/. A perceptual bias favoring /b/ over /v/ emerged in two experiments. In Experiment 1, a directional asymmetry was observed in discrimination; infants noticed when /vas/ changed to /bas/ but not when /bas/ changed to /vas/. In Experiment 2, a robust listening preference favoring stop-initial /bas/ was evident in responses from the same infants. This is the first study to show a perceptual bias related to consonant manner and to directly measure a consonant perception bias within the same infants. These data encourage further efforts to extend the NRV principles to perception of consonant manner. These findings indicate that we need to reform our view of infant speech perception to accommodate the fact that both discrimination abilities and biases shape speech perception during infancy.