The visual evoked response to word stimuli in the visual fields

The visual evoked response (VER) has been considered an objective indicator of visual and perceptual processing, although as yet there is no clear evidence of a relationship between visual recognition and electrophysiological activity. The present study was performed to determine whether VER's can provide indications of differences in responses to word stimuli presented in different parts of the visual field. Additionally, evidence was sought as to whether the left and right hemispheres process visual information symmetrically. In 20 adult subjects with normal binocular vision, VER's were recorded simultaneously from left and right hemispheres in response to the repeated presentation of a three-letter word in each of 7 visual field locations. VER's of any subject in response to one stimulus site were consistent and repeatable; intersubject variation was large. For subject comparison, amplitude of VER was the measured response. No significant or consistent amplitude characteristics were identified that related to recognition of the stimulus. From comparison of responses to the different field locations, central stimulation (at 0 degrees) evoked the largest peak-to-trough amplitude (X=8.21 uV+/- 2.56). Amplitudes tended to be larger at 4 degrees than at 2 degrees from center; left field stimulation tended to give larger amplitudes than right field; however, these trends were larger than from the left, this difference was not valid since 11 subjects had larger right hemisphere responses, whereas 9 had larger amplitudes from the left hemisphere. Thus, the study suggests that the VER reflects some net electrical activity from the recording sites that may be traced to an external sensory stimulus and shows that this activity is symmetrical for each hemisphere.