The Effects of Attention and Adaptation Duration on the Motion Aftereffect

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The motion aftereffect (MAE) is the perception of illusory motion following extended exposure to a moving stimulus. The MAE has been used to probe the role of attention in motion processing. Many studies have reported that MAEs are reduced if attention is diverted from the adaptation stimulus, but others have argued that motion adaptation is independent of attention. We explored several factors that might modulate the attention−adaptation relationship and therefore explain apparent inconsistencies, namely (a) adaptation duration, (b) motion type: translating versus complex, and (c) response bias. Participants viewed translating (Experiments 1a and 2) or rotating (Experiment 1b) random dot patterns while fixating a central letter stream. During adaptation, participants reported brief changes in the adaptor speed (attention-focused) or the presence of white vowels within the letter stream (attention-diverted). Trials consisted of multiple adaptation-test cycles, and the MAE was measured after each adaptation period. Across experiments, focused attention produced significantly larger MAEs than did diverted attention (15% change, Cohen’s d = .41). Attention affected the MAE asymptote, rather than its accumulation rate, and had larger effects for translational than for complex motion. The effect of attention remained evident after controlling for response bias. Our results suggest that attention affects multiple levels of the motion-processing hierarchy: not only higher level motion processing, as seen with apparent motion, but also low-level motion processing, as evidenced by the MAE.

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