Abstract
Prior physiological studies indicate that gaze direction modulates the gain of neural responses to visual stimuli (Andersen and Mountcastle 1983). Although several relevant psychophysical reports are available (Kohler, 1964; Leppmann & Wieland, 1966), the gaze modulation of visual aftereffects are controversial (McCullough, 1965; Harrington, 1966) with few exceptions (Meyhew, 1973; Nishida et al., 2001). Here, we test gaze modulation using color and depth aftereffects. Using methods of constant stimuli to derive psychometric functions we measure the intensity of color and depth aftereffects primarily utilizing three paradigms: 1) Classical Retinotopy (Subjects maintain constant fixation throughout adaptation and testing. Adaptation stimuli are always presented on the fovea while test stimuli are presented at varying retinal positions), 2) Balanced Alternating Adaptation (Similar to Mayhew. At regular intervals during the adaptation period, subjects alternate fixation between two loci with opponent adaptation stimuli. For testing, refixation position varies and the test stimuli are presented at the fovea), and 3) Alternating Fixation Adaptation (Similar to 2, except only one of the alternating fixation loci includes an adaptation stimuli). In both color and depth aftereffects we find strong spatial tuning (1) centered at the location of adaptation with significant effect beyond the retinotopic adapted region. Alternating fixation (2,3) shows strong gaze dependent aftereffects for both color and depth. Alternating adaptation paradigms provide a qualitatively different means of testing the spatial tuning of aftereffects and may prove a more sensitive measure of gaze modulation. The results provide strong evidence for (a) gaze modulation of aftereffects, (b) generality of the modulation across two visual attributes, and (c) perceptual correlates of the modulation of neural activity by gaze direction.