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Maria Pereverzeva, Scott O. Murray; Separating changes in reflectance and illumination in early human visual cortex. Journal of Vision 2009;9(14):73. doi: https://doi.org/10.1167/9.14.73.
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© ARVO (1962-2015); The Authors (2016-present)
To estimate object lightness, or perceived surface reflectance, the visual system has to discount illumination conditions. How this discounting is achieved is a central question in understanding lightness constancy. We investigate the neural mechanisms of lightness constancy by measuring the fMRI response in early visual cortex to luminance modulations of a rendered three-dimensional sphere. In one condition, the luminance modulation was consistent with a change in illumination and in a second condition it was consistent with a change in surface reflectance. We observed a strong correlation between neural activity in early retinotopic visual areas V1–V3 and perceived lightness. Specifically, even though the luminance modulations were identical in the two conditions, the fMRI response was significantly reduced when the luminance modulation was consistent with a change in illumination. This result is in-line with the idea that the visual system separates and at least partly discounts illumination information in early stages of processing, possibly forming the basis of lightness constancy.
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