Differences in the P3 component of the cortical evoked potential elicited by syllables and pure tones

Abstract

Hemispheric asymmetries of the cortical evoked potentials in response to speech stimuli have been reported by several laboratories. The present experiment sought to determine whether a paradigm which elicited the P3 wave, which occurs when the subject attends to an infrequent stimulus, would enhance such differences. Eight subjects listened to four sets of stimuli, two consisting of the CV syllables /pa/ and /ba/, and two consisting of pure tones at 250 Hz and 600 Hz. Each stimulus appeared as the frequent and infrequent stimulus, in a ratio of 1:4, in one of the sets. The subjects' task was to count the infrequent stimulus in each set. Separate averaged evoked responses were computed for each of the four conditions, from recording sites at the vertex and homologous points over the right and left temporal areas. The P3 waves elicited by the infrequent stimuli differed considerably between conditions (speech or tones) but within-condition asymmetries between the temporal area electrode sites were not observed.