Abstract
The brain pools various sensory inputs together to form a unified perception of the world. Since our perception relies on the harmony of neural activities, adaptation mechanisms seem to exist to adjust the neural gain for maintaining correspondence between reality and our percept. While studies on unimodal aftereffects imply adaptation upstream to the stage of multi-sensory integration, very few examined the probability of crossmodal transfers of aftereffects (Kitagawa & Ichihara, 2002) and downstream adaptation is still unknown. Such mechanisms, adaptation after multi-sensory integration, would predict symmetric crossmodal transfers of aftereffects, namely, exposure to stimulus in modality A alone inducing modulation to modality B and vice versa (B to A). We tested this view using the orthogonal motion aftereffect. To examine the transfer of auditory to vision (AV), subjects were adapted to reciprocal auditory motion (burst of white noise moving through 4 speakers) while fixation and asked to report the visual motion (2AFC, horizontal or vertical) of dynamic random dots presented 1s after the offset of adaptation. We used mirrors to match the perceived center positions of the auditory and the visual stimulus. For the vision to auditory condition (VA), adaptation stimulus was a visual target moving reciprocally and subjects again reported the perceived motion (2AFC) of the auditory test stimulus, a superimposed auditory motion of horizontal and vertical (8 speakers). MAE was quantified by the shift of perceptual null points. There were significant shifts in null points for both the AV and VA conditions, such that visual motion in the AV condition and auditory motion in the VA condition were perceived more orthogonal to the adapted direction. The result provides an earliest evidence of bidirectional transfer of the orthogonal MAE, supporting the hypothesis that adaptation may also occur after multisensory integration.