Hemispheric differences in stimulus identification

Subjects were presented with either verbal (letters) or nonverbal (outline forms) stimuli to their left or right cerebral hemispheres. Verbal items presented with a lateral masking stimulus were identified more quickly and accurately when presented to the right hemisphere rather than to the left. When the letters were presented without a masking stimulus, weak hemispheric effects were obtained. Nonverbal forms demonstrated faster reaction time and fewer errors for right-hemisphere presentations under both masked and unmasked conditions. Retinal locus of the display item was also varied and produced faster responding with fewer errors when the stimulus was presented foveally rather than peripherally under all display conditions. These effects were attributed to the use of a manual response procedure that effectively reduced the ability of subjects to employ names for the stimulus objects.