Early Speech Perception and Later Language Development: Implications for the “Critical Period”

In this article, we present a summary of recent research linking speech perception in infancy to later language development, as well as a new empirical study examining that linkage. Infant phonetic discrimination is initially language universal, but a decline in phonetic discrimination occurs for nonnative phonemes by the end of the 1st year. Exploiting this transition in phonetic perception between 6 and 12 months of age, we tested the hypothesis that the decline in nonnative phonetic discrimination is associated with native-language phonetic learning. Using a standard behavioral measure of speech discrimination in infants at 7.5 months and measures of their language abilities at 14, 18, 24, and 30 months, we show (a) a negative correlation between infants’ early native and nonnative phonetic discrimination skills and (b) that nativeand nonnative-phonetic discrimination skills at 7.5 months differentially predict future language ability. Better native-language discrimination at 7.5 months predicts accelerated later language abilities, whereas better nonnative-language discrimination at 7.5 months predicts reduced later language abilities. The discussion focuses on (a) the theoretical connection between speech perception and language development and (b) the implications of these findings for the putative “critical period” for phonetic learning.