Hemispheric differences in stimulus identification

Abstract

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.The usual paradigm for measuring hemispheric processing effects on the accuracy of stimulus identification consists of tachistoscopically presenting items in either the right or left visual field. If the subject is fixating on a central point and the stimulus is presented at an exposure duration of less than 250 msec, the item is projected to the hemisphere contralateral to the visual field in which it appears. The subject is then required to indicate, either verbally or by pointing to the test item from an array of possible items, what he saw. Considering identification studies that presented stimulus items to only one visual field on any given trial, verbal items are correctly identified more often when they are projected to the left than when they are projected to the right hemisphere. These verbal stimulus materials have included single letters (Bryden, 1965(Bryden, , 1966

Integrative and interruptive mechanisms in peripheral and hemispheric masking

“…The experiment was similar to other masking studies that varied the location of the stimulus presentations in the visual fields (Lefton, 1972;McFadden & Gummerman, 1973;Polich, 1978;Proudfoot , 1982;Saccuzzo et al, 1982;Ward & Ross, 1977), and it is a partial replication of the work by Saccuzzo et al that examined masking in higher cortical regions . It is believed that presentations to opposite visual fields result in contralateral stimulus projections beyond Area 17 in the visual cortex (McFadden & Gummerman, 1973;Saccuzzo et al, 1982).…”

Color segregation and selective attention in a nonsearch task

“…For all types of mixed-noise displays, performance degraded more when the more strongly interfering type of noise element was positioned in the left rather than in the right visual field. Apparently, the perceptual impact of a noise element was stronger when the element was presented to the left visual field/right hemisphere than when presented to the right visual field/left hemisphere (cf', Hellige, 1980;Hellige &: Webster, 1979;Polich, 1978). In agreement with the hypothesis that the more strongly a noise element interfered, the greater was the benefit by color segregation of that noise element from the target, improvement in performance was greater by color segregation of a noise element in the left than by one in the right visual field.…”

Dual hemispheric processing in a letter matching task

“…This finding is difficult to interpret, in view of the fact that it was absent in the previous experiment. However, it is interesting to note that such an effect is not unprecedented (e.g., Bryden, 1966;Crovitz & Schiffman, 1965;Polich, 1978).…”