Effect of attention on the VEP in binocular and monocular conditions

To study the effect of voluntary concentration on the visual evoked potential (VEP) with monocular and binocular rivalry stimulation, pattern reversal VEPs were recorded using 5.5 min arc and 50 min arc check sizes. Subjects viewed the VEP stimulus with the left eye and a light emitting diode (LED) with the right eye. They were asked to concentrate on either the VEP stimulus or the LED. The two targets were arranged so that the left eye remained accurately focused on, and directed to, the centre of the VEP stimulus throughout the recordings. The binocular VEP wave became attenuated when the subject concentrated on the LED. The wave was reduced to around two-thirds of the amplitude present when concentrating on the VEP stimulus. This reduction in the VEP amplitude is considered to be due to a binocular interaction because there was a lack of amplitude attenuation when the experiment was repeated with monocular conditions. The results also suggest that the wave is smaller when the non-dominant eye receives the VEP stimulus compared with that when the dominant eye is stimulated by the VEP target.