| This study explored the role of attention in the development of tone and vowel perception skills in infants through the use of auditory and visual associative learning and the functional nature of Mismatch Responses (MMRs) in infants. Two different infant MMR responses have been observed to speech sound changes, one positive and the other negative in polarity. Current evidence suggests that the negative MMR is the precursor of the adult MMN, whereas the positive MMR may index recovery from refractoriness or an orienting response. Event Related Potentials (ERPs) were collected to tones (1000Hz vs. 1200 Hz) and Consonant-Vowel-Consonant (CVC) words ([bIp] vs. [bepsilonp]) in two different conditions designed to focus attention differently. In the contingent condition, a picture of a smiling woman's face always followed occasional deviant auditory stimuli. In the non-contingent condition, the women's face followed 100% of the time in the tone experiment and the women's face randomly followed the standard [bepsilonp] on half the occasions, and the deviant [bIp] on the other half in the speech experiment. A statistically significant difference was not found between the contingent and non-contingent task in the tone experiment. Both conditions elicited a more negative deviant waveform than the standard waveform at frontal sites. Negative MMRs peaked around 200 ms when attention was focused to the change in the contingent condition for the speech experiment. A significant difference was seen in the amplitude of the MMR to the deviant in the contingent vs. non-contingent conditions (F (20, 180) = 2.67, p = 0.001). The difference was greatest at left frontocentral sites. The elicitation of the negative MMR (the assumed precursor of the adult MMN) to this fine-grained phonetic difference appears to require attention in the first year of life. This is most likely because robust representations have not yet been constructed to allow for automatic and preattentive discrimination. |
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