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Bruno Breitmeyer, James Brown, Ralph Hale, Richard Plummer; Effects of Inducer Contrast on Simultaneous Brightness and Poggendorf Illusions. Journal of Vision 2017;17(10):472. doi: https://doi.org/10.1167/17.10.472.
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© ARVO (1962-2015); The Authors (2016-present)
While the striate cortical contrast-response function is nearly linear, the extrastriate function shows a steep, nonlinear increase for contrasts ranging from 0.0 to 0.30 and a gradual increase toward response saturation for higher contrasts. The extrastriate response comports with: 1) the tendency for neural activity in the ventral cortical pathway to shift from stimulus-, energy-dependent coding at low cortical levels to percept-, information-dependent coding at higher levels; 2) the majority (≈70%) of local contrasts in natural scenes being ≤ 0.30; and consequently, 3) the need to amplify the contrast response to the low-contrast inputs at higher percept-dependent cortical coding to optimize the extraction of perceptual information. Past research has shown that Simultaneous Brightness induction can be explained by the antagonistic center-surround organization of neural receptive fields at low (striate and pre-striate) levels of processing whereas the Poggendorf illusion appears to additionally rely on higher percept-dependent (post-striate) processing. As inducer contrast increases from 0.0 to 0.30, the Poggendorf illusion should yield a strong nonlinear increase whereas the Simultaneous Brightness illusion should yield a nearly linear increase over the same range of contrasts. We normalized contrast-dependent changes of both illusions so that the changes ranged from 0.0 (at inducer contrast = 0.0) to 1.0 (at inducer contrast = 1.0). As expected, for inducer contrasts ranging from 0.0 to 0.32, we found that the illusion magnitude increased steeply and nonlinearly with inducer contrast for the Poggendorf illusion but nearly linearly for the Simultaneous Brightness illusion. We conclude that 1) the Poggendorf illusion relies more heavily on high-level, percept-dependent cortical processing than the Simultaneous Brightness illusion and, more generally, 2) differences between contrast-dependent changes may be a useful tool in determining the relative level of cortical processing of many other visual effects.
Meeting abstract presented at VSS 2017
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