A waveform dissimilarity of auditory evoked potentials induced by the stimulation of meaningful nouns

Hemispheric asymmetry in language processing was investigated using an auditory evoked potential as the index for neurophysiological activity. Subjects were given the task of recognizing and classifying typical Japanese nouns, responding to nonsense syllables and responding to tone pips. Fourteen subjects participated and the AEPs of 12 subjects from the frontal, central and parietal regions were adopted for subsequent analyses. Correlation coefficients between the right/left AEPs from homologous scalp regions and a waveform similarity curve analysis that can indicate the similarity of two AEPs segmentally and successively, were adopted to provide the intra-individual symmetry index. Results were as follows: (1) The waveforms between the right/left AEPs induced by meaningful nouns were significantly dissimilar than those induced by nonsense syllables and tone pips; (2) the dissimilarities occurred mainly at 160 msec and 350 msec from the onset of the first syllable on the frontal and central regions. These findings may reflect the hemispheric asymmetry of neurophysiological activity in language processing.