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 N1c 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) or a speech consonant /da/ (female voice recording; 7 ms VOT; 212 ms; 72 dB SL; ISI=600 ms; 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×electrode, and age×N1 component, respectively. Results: Left hemisphere N1a was mature before age 3 whereas the right hemisphere N1a matured around 7–8 years. The vertex N1b showed a parietal distribution which shifted anteriorly with age. The N1c showed age- and stimulus-related changes. The N1c measured over the left hemisphere matured earlier than the N1c over 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.