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Nathan H Heller, Patrawat Samermit, Nicolas Davidenko; Orthogonal and parallel rebounding aftereffects produced by adaptation to back-and-forth apparent motion. Journal of Vision 2019;19(10):286a. doi: https://doi.org/10.1167/19.10.286a.
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It has been shown that adaptation to superimposed, balanced opposite motion directions (i.e. transparent motion) induces unidirectional motion aftereffects along the axis orthogonal the adaptation directions, not parallel to them (Grunwald & Lankheet, 1996). However, we recently showed in a striking new effect that adaptation to alternating (rather than superimposed) balanced motion directions leads to percepts of rebounding or back-and- forth motion that is parallel to the adaptation directions. In order for adaptation to produce these parallel rebounding aftereffects, the transition between alternate opposing directions must be sufficiently slow, around 1–3Hz (Davidenko, Heller, Cheong, & Smith, 2017; Davidenko & Heller, 2018; Heller & Davidenko, 2018). Here we asked whether adaptation to alternating directions at higher speeds would produce orthogonal rebounding after-effects. In this study participants adapted for 2, 2.667, or 3.333 seconds to rapidly alternating horizontal or vertical motion (9 Hz alternating speed; 18, 24, or 30 alternations) or slowly alternating motion (1.5 Hz; 4, 5, or 6 alternations). Participants then reported perceived direction on two ambiguous test frame transitions composed of uncorrelated random dots presented at 1.5 Hz. We coded responses as parallel rebounding aftereffects if reports followed the same axis as the adaptation (e.g. LEFT-RIGHT-LEFT-RIGHT followed by LEFT-RIGHT response). When responses switched axis (e.g. LEFT-RIGHT-LEFT-RIGHT followed by UP-DOWN response) we coded those as orthogonal rebounding aftereffects. The proportion of orthogonal and parallel rebounding aftereffects were significantly modulated by alternation speed [paired t test: t(33) = 2.9, p = .007], with the orthogonal effect reported on 23.1 % of fast trials and 15.1% of slow trials, and parallel effect reported on 16.4% of fast trials and 20.3% of slow trials. Thus, adapting to opposing directions not only result in unidirectional orthogonal aftereffects, but also leads to rebounding orthogonal or parallel aftereffects, depending on the speed of the adapting, rebounding motion.
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