The effect of stimulus duration and inter-stimulus interval on cortical responses in infants

Cortical auditory evoked potentials (CAEP) were recorded from ten normal-hearing infants, aged 3 to 7 months, using the natural speech segments /m/ and /t/. The aim was to investigate the effect of selected stimulus durations and inter-stimulus intervals (ISIs) on infant responses. In the first experiment, various stimulus durations were used but the ISI was fixed. Results showed no significant difference in the latency of the first positive peak (P1) with changes in stimulus duration, but there was a minor increase in amplitude when duration increased from short to medium length. In the second experiment, medium length stimuli were presented with various ISIs. Results showed that as the ISI increased, P1 latency was constant but its amplitude increased nonlinearly for /t/ only. It appears therefore, that for the selected speech stimuli there was no clear advantage in using stimulus durations beyond 35 ms and ISIs beyond 1125 ms in infant assessments.