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Peter Scarfe, Alan Johnston; Perception of motion from the combination of temporal luminance ramping and spatial luminance gradients. Journal of Vision 2010;10(7):847. doi: 10.1167/10.7.847.
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© ARVO (1962-2015); The Authors (2016-present)
It has been shown previously that illusory motion is seen when local temporal ramp after-effects are viewed slightly out of register with a static display of light or dark regions (Anstis, 1990, Perception, 19, 301-306). In the research presented here we investigated the apparent motion produced by after-effects such as these. In a first experiment observers adapted to a radial pattern of ramping lightening or darkening regions, which were replaced by static luminance gradients. The combination of temporally ramping luminance after-effects and physically present luminance gradients induced clear rotational motion. The speed of this rotation was measured in a binary choice task. The speed of rotation was very regularly related to the magnitude of the luminance gradient, shallower gradients resulted in faster rates of rotation, but the ramping rate during adaptation had no effect on the speed of perceived rotation. In a second experiment we adapted observers to a radially interleaved spatially separated pattern of static spatial luminance gradients and temporal luminance ramps. After adaptation we presented observers with a static uniformly mid-grey circle. Although this test pattern contained no physical luminance change, either spatially or temporally, observers perceived radial expanding or contracting motion, which was dependant on the direction of the temporal luminance ramping during adaptation. This suggests that temporal ramp after-effects and spatial gradient after-effects were spatially integrated to produce illusory motion. Overall our results point to a precise integration of temporal luminance ramping and spatial luminance gradients in the computation of image motion, whether these are physically present or in the form of perceptual after-effects.
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