Acoustic variability affects asymmetry in infant speech discrimination

Abstract

From birth, infants are capable of discriminating speech sounds that occur cross-linguistically, but by their first year, infants have difficulty discriminating most non-native contrasts (Werker and Tees, 1984). Yet, language experience is not the only factor affecting discrimination. Further research into language-specific perception reveals asymmetries occur in the discrimination of vowels according to perceptual space (Polka and Bohn, 2003) and consonants based on frequency in the input (Anderson etal., 2003). It might be that acoustic variability also causes asymmetries in infant speech perception. Seventy-six 6- and 9-month olds participated in a discrimination task comparing bilabial and velar stop - /l/ onsets to unattested coronal stop - /l/ onsets (e.g. /kla/ - /tla/; /pla/ - /tla/) in both voiced and voiceless conditions. Infants successfully discriminated coronal from bilabial onsets (p<0.05), but not velar (p>0.05), with no effects of age or voicing. Adult productions of the attested clusters were subjected to an acoustic analysis. Of the four tested characteristics, higher standard deviations were found in velar onsets (/kla/ > /pla/: F2 onset and liquid duration; /gla/ > /bla/: F2 slope, VOT, and liquid duration). This suggests that acoustic variability in the input affects infants' speech discrimination.