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Maarten J. Smagt, Thomas D. Albright, Gene R. Stoner; Motion after-effect direction depends on depth ordering in the test pattern. Journal of Vision 2001;1(3):408. doi: 10.1167/1.3.408.
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A horizontally moving grating can be made to appear to move either upward or downward by introduction of appropriate depth-ordering cues (Duncan et al., J. Neurosci, 2000). Here we show that the illusory motion perceived in the motion after-effect (MAE) is similarly affected by these contextual cues. Eight naïve observers adapted 30s to a horizontally moving vertical grating, viewed through a diamond-shaped aperture. Random spatial texture was added to the bright regions of the grating to ensure the percept of horizontal motion. The entire adapting stimulus was at zero-disparity. The four panels defining the diamond-shaped aperture of the static test stimulus had one of two depth configurations: 1) Upper-left and lower-right panels in front of the grating, lower-left and upper right behind, or 2) vice-versa. The test grating had no texture and zero disparity. Stereo depth for these ‘barber-diamond’ stimuli (op. cit.) was achieved via anaglyph glasses. Although the motion of the adapting stimulus was exclusively horizontal, the direction of the MAE tended to deviate either upwards or downward, such that the physically static grating appeared to slide obliquely beneath the near panels of the test stimulus. A test pattern without the depth ordering but otherwise identical, did not reveal any systematic bias. Depth-ordering cues thus affect the interpretation of both real and illusory (MAE) motion, suggesting that motion adaptation occurs (at least in part) prior to the stage at which these contextual cues act.
DuncanAlbrightStoner(2000). Occlusion and the interpretation of visual motion: Perceptual and neuronal effects of context. J. Neurosci 20, 5885–5897.
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