Abstract
In many cortical areas including V1 (Trotter & Celebrini, 1999), the direction of gaze can modulate the gain of neuronal response to visual stimuli, presumably for the conversion from gaze-dependent to gaze-independent coordinates. In order to find a perceptual correlate of neural gaze modulation, we investigated whether gaze direction modulates visual aftereffects. We measured the effects of varying gaze direction between adaptation and test on (1) the tilt aftereffect, (2) the size aftereffect, and (3) post-adaptation threshold elevation for Gabor patterns by using the staircase method with a top-up adaptation procedure. Subjects always had to keep their head direction straight ahead, hence had to rotate their eyes in the head to gaze directly at a pattern. The adaptation pattern was presented 32-deg to the left or to the right. The test was presented pseudo-randomly on the same or opposite side of the midline as the adaptation stimulus. In either case, the subjects had to make a two-step gaze shift from adaptation to test patterns via a marker on the midline. The magnitude of the tilt aftereffect was smaller by about 20% when the adaptation and test were presented on opposite sides of the midline than when they were on the same side. Modulation by gaze direction was found even when accurate matching of retinal image was accomplished by means of an afterimage alignment procedure, although the modulation was greatly reduced when the stimuli were seen monocularly. Gaze modulation was not robustly found for the size aftereffect (2) and threshold elevation (3). We nevertheless could replicate the gaze-contingent motion aftereffect (Mayhew, 1973) in which alternate viewing of clockwise and anti-clockwise rotations at different gaze directions resulted in a direction reversal of the aftereffect in accordance with a gaze shift. These results suggest that the gaze direction can modulate visual aftereffects, though modestly and possibly not all aftereffects.
TrotterY.CelebriniS.(1999). Gaze direction controls response gain in primary visual-cortex neurons. Nature, 398(6724), 239– 242.