Reaction times and evoked potentials as indicators of hemispheric differences for laterally presented name and physical matches.

Abstract

Letter pairs, which could be name matches, physical matches, or mismatches, were presented at fixation or 2.5 degrees left or right of fixation. During different experimental sessions, the locations and the types of matches were fixed (and therefore known in advance by the subject) or were randomized. Right visual field superiority in reaction time occurred for name matches only when location was randomized, and then the extent of the superiority depended on whether the types of match called for were predictable. Evoked potentials to the letter pairs during this task revealed hemispheric and neural pathway differences that were independent of expectancy condition. Right hemisphere responses were larger than left. For some components, amplitudes were smaller and latencies were shorter for direct than for indirect projection of stimuli to each cerebral hemisphere. Indirect-direct differences in P300 amplitude varied for each cerebral hemisphere according to whether a physical or name match occurred. The P130 and N170 components manifested hemispheric differences that depended on whether the two letters of a pair were in the same or different cases.