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Yasuhiko Saito, Kenzo Sakurai; Inverted vection as a function of vection strength induced by background motion. Journal of Vision 2014;14(10):1348. doi: 10.1167/14.10.1348.
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Nakamura and Shimojo (2000) reported inverted vection, illusory self-motion perception in the same direction as a foreground motion, induced by a combination of the slowly moving foreground and an orthogonally fast moving background. They also claimed that inverted vection occurred when the orientation of the self was destabilized by the motion of the background (Nakamura & Shimojo, 2003). If that were the case, inverted vection strength would increase as a function of the strength of vection induced by the moving background. We conducted 2 experiments to test this possibility by varying the velocity of moving random-dots of the background (experiment 1) and their motion direction coherence (experiment 2). Observers wore a shutter goggle and viewed stereoscopic stimuli, i.e, the background pattern 15cm farther and the expanding/contracting random-dots foreground pattern 15cm nearer than the screen. Observers reported the perceived self-motion duration and its direction (rightward/leftward or forward/backward) by pressing one of the 4 response keys, each for vection by background and for inverted vection by foreground. In experiment 1, 6 velocities (1, 5, 10, 15, 20, 25 deg/sec) for each direction were applied to random-dots' horizontal motion of the background. Results showed that the total duration of vection increased from 1 to 10 deg/sec then saturated up to 25 deg/sec, while the total duration of inverted vection increased as the velocity was higher than 10 deg/sec. In experiment 2, 11 coherence values (0 ~ 100% in 10% step) were applied to random-dots' motion direction of the background. Results showed that the total duration of vection increased from 0 to 50 % then saturated up to 100%, while the total duration of inverted vection increased as the coherence was higher than 50%. These results support Nakamura & Shimojo's claim that inverted vection occurs when the orientation of the self is destabilized.
Meeting abstract presented at VSS 2014
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