Impact of second-language experience in infancy: brain measures of first- and second-language speech perception

Abstract

Language experience 'narrows' speech perception by the end of infants' first year, reducing discrimination of non-native phoneme contrasts while improving native-contrast discrimination. Previous research showed that declines in non-native discrimination were reversed by second-language experience provided at 9-10 months, but it is not known whether second-language experience affects first-language speech sound processing. Using event-related potentials (ERPs), we examined learning-related changes in brain activity to Spanish and English phoneme contrasts in monolingual English-learning infants pre- and post-exposure to Spanish from 9.5-10.5 months of age. Infants showed a significant discriminatory ERP response to the Spanish contrast at 11 months (post-exposure), but not at 9 months (pre-exposure). The English contrast elicited an earlier discriminatory response at 11 months than at 9 months, suggesting improvement in native-language processing. The results show that infants rapidly encode new phonetic information, and that improvement in native speech processing can occur during second-language learning in infancy.

Keywords: Event-related potentials (ERPs); infants; language development; mismatch negativity; second-language learning; speech discrimination; speech perception.

Figure 1

Example of a Spanish-language exposure session. Five native Spanish-speaking researchers (4 female, 1 male) served as “tutors” who used books (10 minutes) and toys (15 minutes) while talking to the infants. Each infant participated with at least 3 different tutors at least 3 times, for a total of 12 sessions. Infants’ parent/caregiver accompanied them, and either one or two parent-infant dyads were present during the sessions.

Figure 2

Grand-averaged pre- (9-month) and post-exposure (11-month) ERPs to syllables in double-oddball paradigm. Enlarged area displays results at a representative electrode site (CZ). Infants heard 700 standard stimuli ([ta], black line), 100 English deviants ([t^ha], blue line), and 100 Spanish deviants ([da], red line). Negative voltages (microvolts) are plotted upward.

Figure 3

Mean pre- and post-exposure ERP N200-250 and N250-450 peak amplitudes (microvolts) to the 3 stimuli, averaged across 13 electrode sites (5 left hemisphere, FP1, F3, FC1, C3, CP1; 5 right hemisphere, FP2, F4, FC2, C4, CP2; and 3 midline, FZ, CZ, PZ). Error bars represent + 1 SE. Asterisks represent significantly larger amplitudes to deviants vs. the corresponding standard stimuli.