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Takeharu Senoo, Takao Sato; The contribution of higher-order motion on vection and body sway. Journal of Vision 2003;3(9):412. doi: 10.1167/3.9.412.
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Purpose: We examined contributions of first- and higher-order motion components on vection and body-sway by using compound sinusoidal 2f+3f gratings. The stimulus comprised of second (2f) and third (3f) harmonics of non-existent fundamental frequency (f). When it was shifted by 90 deg of fundamental frequency, directions of first- and higher-order motions were opposite, while perception was dominant in the direction of higher-order motion. Method: The 2f+3f gratings with a fundamental frequency of 0.3 c/d were used. Regular, luminance defined gratings with the same fundamental f were also used. The stimulus was shifted by 90 deg phase angle with an SOA of 150ms and no ISI. Higher-order motion was perceptually dominant for 2f+3f stimuli. The stimulus subtended 55 × 55 deg visual angle. Subjects viewed the center of stimulus at a distance of 2.5m on a body sway measure board. In Exp. 1 drifting horizontal gratings were presented to evaluate vection. Subjects were asked to keep press a button specified for the vection direction while they perceive vection, and the duration of button presses were recorded. In Exp. 2, vertical gratings were used to evaluate body sway. Body sways were recorded with a body sway measure board at 10 Hz. Perceived motion directions were also recorded in either experiment. Motions were presented for 9 times for 30 sec each time and there was a 30 sec rest period in between. Results: Higher-order motion induced both vection and body sways. Both were observed in the opposite direction to perceived direction for the two types of stimuli. The magnitude of body sway and vection were larger for normal gratings than for 2f+3f gratings, but wave forms of body sways were quite similar.
Conclusion: These results indicated that both body sway and vection are induced by higher-order motions and that both are related to motion perception rather than the existence of internal motion signal.
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