Motion adaptation: net duration matters, not continuousness.

Motion processing is strongly adaptable. Adaptation strength generally increases with motion duration. Little is known, though, about the effect of motion onsets and offsets, which might be relevant if adaptation is not based on motion duration per se, but on the recent cumulated activity of motion-processing mechanisms. Thus, we presented intermittent motion with three different onset rates for adaptation. The duty cycle 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 amplitude of the N2 component of human motion visual evoked potentials was used to quantify adaptation. All three onset rates induced virtually identical amounts of adaptation (occipitally, P=0.71; occipito-temporally, P=0.27), suggesting that the continuousness of the stimulus does not play an important role in motion adaptation. This was confirmed by measuring the motion aftereffect psychophysically.