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Alyssa A. Brewer, Alex R. Wade, Brian A. Wandell; Visual field maps and color signals in human ventral occipital cortex. Journal of Vision 2002;2(7):549. doi: https://doi.org/10.1167/2.7.549.
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© ARVO (1962-2015); The Authors (2016-present)
Introduction: Human occipital cortex contains several distinct foveal representations, but mainly those on the ventral surface respond preferentially to color over luminance-matched stimuli. We made fMRI measurements to learn more about these ventral signals.
Methods: We examined the fMRI BOLD signal in human ventral occipital (VO) cortex using (1) traveling wave stimuli designed to measure eccentric and angular dimensions of retinotopy and (2) color and achromatic patterns matched in luminance but differing in S and L-M signals. Activation maps were transferred onto flattened views of visual cortex, and visual maps were identified to subdivide VO cortex. Regions responding preferentially to chromatic stimuli were located relative to these retinotopic regions.
Results: Large regions of VO cortex contain retinotopic maps. There is a map of the entire contralateral hemifield adjacent to ventral V3. This map fills 4 cm2 of cortex and includes a foveal representation that is confluent with that of areas V1/2/3. The homology of this area to macaque V4 is uncertain because the human map does not extend onto the dorsal surface nor does it surround V1. We propose calling this hemifield representation hV4. A separate and distinct foveal representation is present on the ventral surface anterior to hV4. This foveal representation, located 3–5 cm from the confluent V1/2/3 foveal representation, is larger than the foveal representation in V1. It may be the foveal representation used to define V8, but the orientation of the surrounding map is inconsistent with the V8 definition. Responses to colored stimuli exceed those to achromatic stimuli in V1, hV4, the distinct ventral foveal representation, and other locations within VO cortex.
Conclusion: There is an intricate collection of visual field representations and at least one large foveal representation in VO cortex. Ventral stream responses to S-cone and L-M signals exceed dorsal stream responses.
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