Peripheral and central delay in processing high spatial frequencies: reaction time and VEP latency studies

Visually evoked potentials (VEP) and reaction time (RT) were recorded under stimulation with sinusoidal gratings. Grating spatial frequency (SF) was 0 .5, 5 or 12 ed and grating contrast was varied. Consistent with previous fi ndings, both VEP latency and RT increased with the increase of grating SF a nd with the decrease of grating contrast. It was found, in addition, that R T and VEP latency increased by approximately the same amount when SF increa sed from 0.5 to 5 ed, thus suggesting that the main source of the RT delay at 5 ed in comparison with RT at 0.5 ed is of peripheral origin. However, i n comparison with the data at 0.5 and 5 ed, RT at 12 ed increased much more than VEP latency. We conclude that the RT delay at high SF involves a subs tantial central component in addition to the peripheral delay. (C) 1998 Els evier Science Ltd. All rights reserved.