Abstract
Visual motion processing is strongly susceptible to adaptation. Adaptation strength increases with duration, while little is known about the adapting effect of motion onsets. Animal studies have shown that a number of MT cells produce a transient response to onsets rather than a sustained response [1] and that onset and offset latencies can differ [2]. Using visual evoked potentials (VEPs) and psychophysical measures, we compared 3 different onset rates to assess the effect of motion onsets on motion adaptation in humans. Methods: Intermittent motion was used for adaptation. The duty-cycle (= motion duration vs. total duration) was kept constant at 33% while the rate of motion onsets was either 1.4, 2.8, or 5.6 per second. Stationary stimuli and continuous motion were used as reference conditions. The motion aftereffect was measured psychophysically in 11 subjects with a nulling technique based on motion coherence. VEPs were recorded from 7 subjects. Results: For intermittent adaptation, on average 26% coherent motion was required to cancel the motion aftereffect in the psychophysical experiment. There was no appreciable dependence on the motion onset rate. 7% (indicating a direction bias) and 29% coherence were required for stationary stimuli and continuous motion, respectively. VEP amplitudes were on average reduced by 70% after intermittent adaptation, relative to stationary adaptation. No sizable difference was found between the three motion onset rates. Adaptation with continuous motion resulted in a 95% decrease in VEP amplitude. Conclusion: Both VEPs and psychophysical results suggest that motion adaptation is independent of the number of motion onsets.
[1]
LisbergerSGMovshonJA(1999). J Neurosci 19:
2224–
2246
[2]
BairWCavanaughJRSmithMAMovshonJA(2002). J Neurosci 22:
3189–
3205