Exploring the natural referent vowel hypothesis in infant perception experiments

Abstract

Directional asymmetries in infant vowel perception studies have led Polka and Bohn [Speech Commun. 41, 221–231 (2003)] to posit the Natural Referent Vowel hypothesis (NRV) according to which vowels that are relatively more peripheral in the F1/F2 space are perceptually privileged vis-a-vis less peripheral vowels. This bias has been observed in preference and in change/no change experiments with infants and with adult non-native listeners. NRV was further tested in headturn (change/no change) experiments with Danish-learning infants. With one important exception, results support the NRV by showing that the predicted asymmetries exist in areas of the vowel space that have not been previously explored. The exception was observed for the Danish front vowel pair /e/-/o//, where NRV incorrectly predicts that a change from the more peripheral /e/ to the less peripheral /o// is harder to discriminate than a change in the opposite direction. Interestingly, the unexpected asymmetry was observed only with infants up to the age of 7.5 months. Older infants showed a nonsignificant trend for an asymmetry in the opposite direction, as predicted by NRV. A modification of NRV to incorporate this finding will be proposed. [Research supported by Grant 25-01-0557 from the Danish Research Council for the Humanities (FKK).]