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Abstract:
Objectives: To examine developmental changes in the N1a, N1b
and N1c evoked by a tone versus a speech consonant (/da/). Methods:
Subjects (n=70 for tones; n=69 for /da/) were grouped into 2yr
intervals (age 3 to 16) and adults. They listened to a tone (2Khz;
36ms; 77 dB SL; ISI=600ms; n=346) or a speech consonant /da/
(female recording; 7ms VOT; 212ms; 72 dB SL; ISI=600ms; n=349)
while watching a Disney screensaver. EEG was recorded from 26
electrodes referenced to Cz. An averaged reference was computed
off-line. Amplitude and latency data were analyzed with
repeated-measures ANOVAs for age x electrode, and age x N1
component, respectively. Results: Left hemisphere N1a was mature
before age 3 whereas the right hemisphere did not mature until
7-8yrs. The vertex N1b showed a parietal distribution which shifted
anteriorly with age. The N1c showed age- and stimulus-related
changes. The left hemisphere N1c matured earlier than the right
hemisphere. The N1c to /da/ matured earlier than that to tones.
Conclusions: Auditory processing undergoes steady and subtle
developmental changes. These changes follow different maturational
patterns depending on the type of stimuli. The evidence suggests
earlier development of the left hemisphere and earlier development
of the generators underlying speech processing.
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