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Harold Bedell, Jianliang Tong; Perception of motion smear during visually induced illusory self motion. Journal of Vision 2009;9(8):688. doi: https://doi.org/10.1167/9.8.688.
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Purpose. Motion of the retinal image during an eye or head movement produces less perceived smear than when the same retinal image motion occurs during stable fixation. However, the reduction of perceived motion smear is asymmetrical, occurring only for targets that move in the opposite direction of an eye or head movement. In this study, we asked if perceived motion smear is reduced also during illusory self motion that is induced by rotation of the visual surroundings. Methods. Four normal observers matched the extent of perceived motion smear produced by a horizontally moving laser spot (velocity = 10 − 60 deg/s) during steady fixation. The observers were surrounded by a 148-cm diameter cloth drum, which either remained stationary or rotated at 15 or 30 deg/s in the clockwise or anti-clockwise direction. During rotation, the observers triggered trials only when they perceived themselves to be moving in the opposite direction of the drum. Horizontal eye movements were monitored and trials were rejected if the eye velocity exceeded 2 deg/s during presentation of the laser target. Results. The extent of perceived motion smear increased systematically from approximately 90 to 190 ms as the target duration increased from 100 to 300 ms. However, perceived smear did not differ significantly between drum-stationary and drum-moving conditions or, in the drum-moving condition, when motion of the laser spot was in the same vs. the opposite direction of perceived self motion. Conclusions. The reduction of perceived motion smear during eye and head movements is attributed to the influence of extra-retinal signals. Although vestibular and visual signals that contribute to perceived self motion are thought to combine in the brainstem, our results indicate these signals must remain separated to some extent, as only the vestibular signals for self motion decrease perceived motion smear.
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