Summated potentials evoked by speech sounds for determining cerebral dominance for language

Ten normal adult right-handed subjects receive phonemic combinations (/epik/, /epak/, /a/, /pi/, /pa/) and pure tones (2500 and 8000 Hz) binaurally through matched earphones. Fifty responses from electrodes at P5, P6, C5, C6, F7 and F8 (referenced to linked mastoids) were summated, and evoked potentials from homologous areas were measured separately and superimposed in order to observe differences. Visual inspection of superimposed responses showed no consistent gross asymmetries that lateralized to either hemisphere. Comparison between amplitude of evoked potentials (N1, P2) at P5 and P6 were not significant (P < 0.05; paired t test). We suggest that our technique may not be a useful clinical test for cerebral dominance.