Abstract
A number of studies showed that infants reorganize their perception of speech sounds according to their native language categories during their first year of life. Still, information is lacking about the contribution of basic auditory mechanisms to this process. This study aimed to evaluate when native language experience starts to noticeably affect the perceptual processing of basic acoustic cues [i.e., frequency-modulation (FM) and amplitude-modulation information] known to be crucial for speech perception in adults. The discrimination of a lexical-tone contrast (rising versus low) was assessed in 6- and 10-month-old infants learning either French or Mandarin using a visual habituation paradigm. The lexical tones were presented in two conditions designed to either keep intact or to severely degrade the FM and fine spectral cues needed to accurately perceive voice-pitch trajectory. A third condition was designed to assess the discrimination of the same voice-pitch trajectories using click trains containing only the FM cues related to the fundamental-frequency (F0) in French- and Mandarin-learning 10-month-old infants. Results showed that the younger infants of both language groups and the Mandarin-learning 10-month-olds discriminated the intact lexical-tone contrast while French-learning 10-month-olds failed. However, only the French 10-month-olds discriminated degraded lexical tones when FM, and thus voice-pitch cues were reduced. Moreover, Mandarin-learning 10-month-olds were found to discriminate the pitch trajectories as presented in click trains better than French infants. Altogether, these results reveal that the perceptual reorganization occurring during the first year of life for lexical tones is coupled with changes in the auditory ability to use speech modulation cues.
Highlights
In the first months of life, infants are able to discriminate almost all phonetic contrasts, including non-native ones (Kuhl, 2004; Werker and Tees, 2005)
The Mandarin-learning infants showed a significant preference for novelty [mean = 59.9%, SD = 15.4; t(15) = 2.58; p = 0.02]
French- and Mandarin-learning 10-month-old infants presented with the same acoustic patterns did not show the same novelty preference, reflecting diverging processing of acoustic cues related to F0 contours
Summary
In the first months of life, infants are able to discriminate almost all phonetic contrasts, including non-native ones (Kuhl, 2004; Werker and Tees, 2005). This so-called “perceptual reorganization” was initially demonstrated by Werker and Tees (1984) who Language experience and modulation cues found that young English-learning infants were able to discriminate a consonant contrast in Hindi between 6 and 8 months of age, but were unable to maintain this ability later on (between 10 and 12 months) while Hindi-exposed infants did so Several studies replicated these initial results with other consonant contrasts using either behavioral or electrophysiological methods (e.g., Tsushima et al, 1994; Best et al, 1995; Cheour et al, 1998; Rivera-Gaxiola et al, 2005). These results demonstrate that speech perception is shaped by language experience during the first year of life, with infants becoming more and more sensitive to their native speech contrasts and less sensitive to non-native ones
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