The Visual Evoked Potential and the Process of Selective Attention Under Conditions of Simultaneous Bilateral Stimulation

Abstract

Visual evoked potentials (VEPs) were recorded from the left and right occipital cortices of 14 male subjects. Single digit numerical stimuli were presented simultaneously in the left and right visual fields (different stimuli for each field) for 50 ms. The subject was asked to attend to one of the fields for a block of 100 trials. The subject was instructed to report verbally the identity of the digits about 1 second after they appeared. A baseline condition requiring no specific focus of attention was introduced to establish a level for any initial hemispheric differences. All subjects received the baseline condition first, and the order of presentation of the attention conditions to the left and right visual fields was randomized across subjects.

The 3-way ANOVA revealed a degree of VEP component specificity, reflecting the influence of the particular variables introduced in the study. The most critical findings for the present hypothesis were the post hoc comparisons between conditions at the right recording site. The latency of the late positive component was found to be significantly shorter when the subject attended to stimuli appearing in the left visual field compared to the baseline condition. No differences were found between the baseline and attend-to-right conditions. This pattern, however, was not noted in the VEPs recorded from the left hemisphere.

The results of the present study are discussed in terms of consistencies with previous VEP research and the the possible relationship between the neurophysiological processes of selective attention and hemispheric function.

Additional information

Notes on contributors

Ronald G. Drozdenko

Joyce Laing works in the Department of Child and Family Psychiatry, Playfield House, Cupar, Fife, and is a Consultant Art Therapist to Psychiatric Hospitals and Prisons and Chairwoman of the Scottish Society of Art and Psychology.