Abstract
Illusory motion of a visual target can be elicited by vibratory stimulation of the neck muscles; after vibration stops, motion in the opposite direction is perceived (Biguer et al, 1988, Brain, 111, 1405–1424). This motion aftereffect could be due to adaptation exclusively at the proprioceptive level, or at a stage where visual and proprioceptive information are combined. To distinguish between these two possibilities, we applied vibratory stimulation to dorsolateral neck muscles for 15-sec periods alternating with 15-sec periods without vibration.Observers (N=26) used a hand-held tracker to indicate perceived motion of the target (an LED). In the critical condition, observers were in complete darkness during vibration, and the LED was only turned on in post-vibration periods. If adaptation was purely proprioceptive, illusory LED motion should have occurred in this condition, but it did not. In a follow-up experiment (N=9), we used a similar method to determine if there was a position aftereffect. The LED was presented intermittently during the test period (for 150 msec, with 1.35 sec of dark periods in between), such that its displacement, rather than motion, could readily be perceived. No aftereffect occurred. Both experiments show that there has to be a visual stimulus during the adaptation period for the aftereffect to occur, at least for the relatively brief adaptation periods used. Proprioceptive mechanisms did not adapt, and visual motion mechanisms were mainly responsible for the illusion. We conclude that they adapt more quickly than the proprioceptive mechanisms from which they receive input.
Support: University of Sydney SESQUI grant to TSC