Time course of motion adaptation: Motion-onset visual evoked potentials and subjective estimates

The aim of this study was to quantitatively describe the dynamics of adapta tion to visual motion with electrophysiological and psychophysical methods in man. We recorded visual evoked potentials (VEPs) to motion onset of rand om dot patterns from occipital and occipito-temporal electrodes during a su ccession of adaptation-recovery sequences. In these sequences the test stim ulus was used to set the adaptation level: seven trials with 70% motion dut y cycle (adaptation) followed by seven trials of 7% motion duty cycle (reco very). In a similar paradigm we determined the length of the perceptual mot ion after-effect to obtain a psychophysical measure of the time course of m otion adaptation. Our results show a highly significant reduction of the N2 amplitude in the maximally compared to the minimally adapted condition (P < 0.001). Electrophysiological and psychophysical results both indicate tha t adaptation to visual motion is faster than recovery: The data were fit wi th an exponential model yielding adaptation and recovery time constants, re spectively, of 2.5 and 10.2 s for the N2 amplitude (occipito temporal deriv ation) and of 7.7 and 16.7 s for the perceptual motion after-effect. Implic ations for the design of motion stimuli are discussed, e.g. a motion stimul us moving 10% of the time may lead to about 30% motion adaptation. (C) 1998 Elsevier Science Ltd. All rights reserved.