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Hiroshi Ashida, Ichiro Kuriki, Ikuya Murakami, Akiyoshi Kitaoka; fMRI adaptation to anomalous motion in the “Rotating Snakes” patterns. Journal of Vision 2010;10(7):827. doi: https://doi.org/10.1167/10.7.827.
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© ARVO (1962-2015); The Authors (2016-present)
Stationary patterns with a specially designed repetitive pattern, such as the “Rotating Snakes” (Kitaoka & Ashida, 2003), can elicit illusory perception of motion. By using a conventional fMRI contrast, we have shown that the “Rotating Snakes” figure activates human MT+ (Kuriki et al, 2008). Activity in V1 was not evident, which can be either because motion signals arise within MT+ (Thiele et al, 2004), or because our motionless control stimulus (for comparison of BOLD signals) that consisted of the same local patterns might have elicited local motion signals (while globally cancelled out). In this study, we used an fMRI adaptation paradigm that does not require an explicit control stimulus, in order to assess direction-selective responses in the visual areas to the “Rotating Snakes” pattern. Four disks that comprised repetitive patterns of white-yellow-black-blue were used. They appeared as rotating in this direction when viewed naturally. After an adapting stimulus (S1) followed by a blank interval, a probe stimulus (S2) of either the same or the reversed color order (hence eliciting illusory motion in the same or the opposite direction) was presented. The spatial phase was altered between S1 and S2 to avoid local coincidence. The fixation mark was blurred to relax fixation to some extent because hard fixation can abolish illusory motion. Attention was controlled by a fixation task. Regions of interest were defined for each participant by separate localizer runs. A 3-T scanner (Siemens Trio Tim) was used. Event-related averages of time-courses revealed larger BOLD responses for reversed S2 than for the same S2 in MT+, indicating direction-specific adaptation. The difference was smaller but evident in V1-V4 and V3A. The overall results suggest that local motion sensors in V1 are indeed activated by the illusion figure, which is in line with most of currently proposed models.
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