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Sei-ichi Tsujimura, Qasim Zaidi; Is induced motion due to position illusions?. Journal of Vision 2002;2(7):374. doi: https://doi.org/10.1167/2.7.374.
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© ARVO (1962-2015); The Authors (2016-present)
A stationary stimulus flanked by moving stimuli can appear to move in the opposite direction. Most explanations involve motion sensitive receptive fields with positive and negative lobes corresponding to opposite directions of motion. For grating stimuli, motion induction exists only for velocities below 2.5 deg/sec. For uniform and shear motion, motion is detected by position tracking at these slow velocities and by motion-energy units at higher velocities (Tsujimura and Zaidi, 2001). We test, therefore, whether motion induction is due to apparent changes of position of the stationary stimulus caused by position changes of the surrounding stimulus, or due to receptive field properties of motion-energy units. A stationary grating (Contrast=.33) was flanked by two moving gratings at the same spatial frequency (SF: 0.5, 1, 2 cyc/deg). We used four kinds of motion for the flankers: 1) A unidirectional moving grating (Contrast=.33; TF: 0.25, 1.0, 4.0 Hz); 2) The moving grating added to a stationary grating (Contrast=.66) of the same spatial frequency. The compound grating's amplitude and spatial-phase oscillate with time, but the motion energy is contributed solely by the moving grating and is unidirectional; 3) A unidirectional grating whose amplitude was modulated like the compound grating; and 4) A grating (Contrast=.66) whose spatial phase was modulated like the compound grating. Observers had to choose whether motion in the central grating was “unidirection”, “oscillation” or “no-motion”. For the compound grating inducers, observers will respond oscillation or unidirection depending on whether motion is induced by position changes or by motion-energy. Observers reported oscillatory induced motion for velocities below 2 deg/sec. At faster velocities no induced motion was reported for any condition. This suggests that induced motion is due to illusory position changes of the central test in the opposite direction to the position changes of the compound grating.
Grants: Novartis Ophthalmics to S.Tsujimura, and NEI EY07556 & EY13312 to Q. Zaidi.
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