Aftereffects of apparent motion adaptation depends on adaptation duration

Abstract

We previously reported a negative, non-location-specific aftereffect of apparent motion (AM) adaptation. For example, perceived AM direction of a bistable motion quartet stimulus spanning a small area (~4×4 deg) exhibited a horizontal bias after 75 seconds of adaptation to a vertically directed AM adaptation stimulation spanning a large area (~8×8 deg). We now further investigated the characteristics of such an AM adaptation phenomenon as a function of adaptation duration (3, 5, 8,10, 12, 15, 30, 45, 60, and 75 seconds). The adapting AM stimulus (~8×8 deg; motion token diameter=1 deg; frame duration=200 msec; ISI=0) was rendered to move back-and-forth horizontally or vertically. The AM test stimulus (~4×4 deg; motion token diameter=1 deg; frame duration=150 msec; ISI=0) was displayed for 15 seconds and the observer was to continuously report the perceived motion direction by holding down on selected keys. Overall, we found a positive AM aftereffect with short adaptation durations (3 and 5 seconds), which switched to a negative AM aftereffect with adaptation durations beyond 8 second. Further analysis of the perceived AM direction immediately upon termination of the AM adaptation revealed a relationship between the immediately-perceived AM duration (AM_{immediate_percept}) and AM adaptation duration (Duration_adaptation), where AM_{immediate_percept} = 8.286*log(Duration_adaptation) - 6.607. Notably, AM_{immediate_percept} became zero when Duration_adaptation was 6.3 sec, revealing a critical adaptation duration, Duration_{critical_adaptation}. Therefore, when Duration_adaptation > Duration_{critical_adaptation}, the AM aftereffect was negative whereas it was positive when Duration_adaptation < Duration_{critical_adaptation}. Interestingly, the latter reveals an AM priming effect. Of significance, these findings suggest stimulus-driven attention-shift by itself is a driver of AM perception. Specifically, short duration of AM stimulation in one direction (horizontal or vertical) facilitates the stimulus-driven attention-shift mechanism in the same direction. Conversely, a longer AM stimulation duration fatigues the stimulus-driven attention-shift mechanism. This consequently biases the perceived AM toward the orthogonal direction.

Acknowledgement: NIH Grant EY023561 and EY023374