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Ryan Wilson, Pauline Pearson, Lorna Jakobson, Bruce Bolster, Jonathan Marotta, Uta Sboto-Frankenstein; Colour and texture processing in human extrastriate cortex: An fMRI study. Journal of Vision 2008;8(6):495. doi: 10.1167/8.6.495.
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Purpose: A neuroimaging investigation was conducted to determine the visual areas of the human brain involved in the discrimination of visual textures and wavelengths.
Methods: Six healthy adults performed forced-choice, match-to-sample tasks within a 1.5T whole body clinical MRI. A block design was used in which the ability to match target and choice patches on the basis of wavelength or texture was assessed separately for isoluminant colour patches from the red, yellow and blue regions of colour space and for Brodatz textures. Participants completed five blocks for each of the four types of visual stimuli.
Results: Relative to a fixation condition, discrimination of colour and visual textures resulted in distinct but significantly overlapping patterns of activation. Both wavelength and texture discrimination were accompanied by increased activation in the left striate and left lingual gyrus. Unique activation for texture or wavelength discrimination was limited to extrastriate areas. Wavelength discrimination uniquely activated more anterior areas, including the left posterior fusiform gyrus (−22, −65, −13) and right lingual gyrus (6,−84,−10); the overall patterns of activation in these areas appeared to demonstrate a dependency on wavelength. Texture showed a smaller regional extent of activation that was more posterior than that for wavelength.
Conclusions: Our study, which employed an active discrimination task rather than the more commonly employed passive viewing, suggests that colour discrimination uniquely activates an area of lingual and fusiform gyri that may represent the human homologue of area v4 in macaque. Furthermore, our results support a human homologue of the wavelength-dependent organization within extrastriate colour processing areas that has been demonstrated previously in macaque. Despite the role of middle temporal areas and anterior fusiform gyrus in form processing, activation in this area was not greater during the discrimination of visual textures than during the discrimination of similar wavelengths.
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