Tracking the development of the N1 from age 3 to adulthood: an examination of speech and non-speech stimuli

Objectives: To examine developmental changes in the N1a, N1b and N1e evoked by a tone and a speech consonant (/da/). Methods: Subjects (n = 70 for tones; n = 69 for /da/) were grouped into 2 year intervals (age 3-16) and adults. They listened to a tone (2 kHz; 36 ms; 77 dB SL; ISI = 600 ms; n = 346) ora speech consonant /da/ (female voice recording; 7 ms VOT; 212 ms; 72 dB SL; ISI = 600 ms; n = 349) while watching a Disney(R) screensaver. EEG was recorded from 26 electrodes referenced to Ct. 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 N1a matured around 7-8 years. The vertex Nib showed a parietal distribution which shifted anteriorly with age. The Nle showed age- and stimulus-related changes. The Nle measured over the left hemisphere matured earlier than the Nlc over the right hemisphere. The Nlc 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. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.