Kurki I, Hyvarinen A, Laurinen P I, 2005, "A reverse correlation study of the spatiotemporal properties of brightness perception in real and illusory stimuli" Perception 34 ECVP Abstract Supplement
A reverse correlation study of the spatiotemporal properties of brightness perception in real and illusory stimuli
I Kurki, A Hyvarinen, P I Laurinen
It has been proposed that the brightness of a uniform surface is determined by the local border contrast responses which are propagated in space by an active, temporally extended filling-in mechanism. Brightness illusions, such as the Craik - Cornsweet - O'Brien illusion where a luminance border gives rise to an illusory brightness percept, have been taken as evidence for this view. Here, a reverse correlation technique was used to assess the spatiotemporal characteristics of brightness perception for both 'real' (luminance defined) and 'illusory' surfaces. A contrast polarity discrimination task was used for (i) a 2.6 deg wide bar of uniform luminance and (ii) a 1-D COC bar in which the edges induce the perception of a 2.6 deg wide illusory bar. The target stimulus was flashed quickly, (4 frames, 67 ms) in the middle of a dynamic 1-D white noise sequence of 36 frames. A fixation mark was used to indicate both the location and the duration of the target stimulus. The resulting spatiotemporal classification images show that the brightness perception in both physical and illusory stimuli is associated with two spatiotemporally distinct responses: (i) a spatially local, temporally short border response, and (ii) a weaker response that was similar in both conditions and corresponds spatially to the brightness percept. This response is spatially and temporally more extended than the border response and resembles the output of a spatiotemporal low-pass filter. The maxima of both responses occur rather simultaneously; we could not find significant delays related to the propagation of the brightness signal. There were no marked differences in the classification images in the real and the illusory conditions, suggesting that both low-contrast physical and illusory surfaces are processed by mechanisms having similar spatiotemporal properties.
[Supported by the Academy of Finland.]
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