Directional motion asymmetry in infant VEPs - which direction?

Monocular viewing during early infancy reveals asymmetries in optokinetic n ystagmus (OKN) and visual evoked potentials (VEPs). This study investigates the VEP asymmetry to see if it is consistent in direction with the OKN asy mmetry. Steady-state VEPs were recorded from infants (5-21 weeks) viewing g ratings that underwent successive displacements in the same direction, left ward or rightward. In addition, transient VEPs were recorded to the two dir ections of an oscillating stimulus. Both tests produced larger VEP amplitud es for nasal-to-temporal compared to temporal-to-nasal movement. Horizontal eye movements were monitored by EOG while viewing these stimuli to test wh ether the asymmetry was a consequence of eye movements. No difference in ev e movements as a function of the stimulus was found. excluding differences in retinal slip as an explanation of the asymmetry. The stronger neural res ponse for nasal-to-temporal displacements is opposite to the asymmetry of O KN. Oculomotor and VEP asymmetries may be related: however this relationshi p is not simply that the stronger neural response, indicated by the VEP, le ads to a stronger optokinetic response. (C) 2001 Elsevier Science Ltd. All rights reserved.