LEFT AND RIGHT VISUAL-FIELD ADVANTAGES ARE A FUNCTION OF SCOTOPIC ANDPHOTOPIC RETINAL ADAPTATION, RESPECTIVELY, IN SIMPLE REACTION-TIME TONEAR-THRESHOLD TARGETS

Modulation of stimulus luminance in a tachistoscopic face discriminati on task has been found to significantly invert visual hemifield advant age in reaction time (RT) (Sergent, 1982a, Sergent, 1982b). However, t here is no more physiological rationale for that than for a similar ef fect, say, of retinal adaptation, and it is even conceivable that the latter may have confounded the former in past experiments, The experim ents reported here were therefore designed to tease out the relative c ontributions of stimulus luminance and of background illumination (i.e ., retinal adaptation) in a simple RT task, Two equally difficult cond itions of dim targets were set up, one with light-adapted subjects and one with dark-adapted subjects. Similarly, two equally difficult cond itions of bright targets were set up with light and dark-adapted subje cts, It was found that dim targets (near detection threshold) yielded a significant right visual field RT advantage in light-adapted subject s and that dim targets (equally near detection threshold) yielded a si gnificant left visual field RT advantage in dark-adapted subjects, Fut ure experiments will determine whether cone-mediated RT to detection i s left hemisphere dominant and whether rod-mediated RT to detection is right hemisphere dominant.