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The Journal of Neuroscience, September 15, 2002, 22(18):8148-8157

Chromatic Light Adaptation Measured using Functional Magnetic Resonance Imaging

Alex R. Wade and Brian A. Wandell

Department of Psychology, Stanford University, Stanford, California 94305

Sensitivity changes, beginning at the first stages of visual transduction, permit neurons with modest dynamic range to respond to contrast variations across an enormous range of mean illumination. We have used functional magnetic resonance imaging (fMRI) to investigate how these sensitivity changes are controlled within the visual pathways. We measured responses in human visual area V1 to a constant-amplitude, contrast-reversing probe presented on a range of mean backgrounds. We found that signals from probes initiated in the L and M cones were affected by backgrounds that changed the mean absorption rates in the L and M cones, but not by background changes seen only by the S cones. Similarly, signals from S cone-initiated probes were altered by background changes in the S cones, but not by background changes in the L and M cones. Performance in psychophysical tests under similar conditions closely mirrored the changes in V1 fMRI signals. We compare our data with simulations of the visual pathway from photon catch rates to cortical blood-oxygen level-dependent signals and show that the quantitative fMRI signals are consistent with a simple model of mean-field adaptation based on Naka-Rushton (Naka and Rushton, 1966) adaptation mechanisms within cone photoreceptor classes.

Key words: fMRI; light adaptation; cones; simulation; V1; Naka-Rushton

Copyright © 2002 Society for Neuroscience  0270-6474/02/22188148-10$05.00/0


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Phil Trans R Soc B, April 29, 2005; 360(1456): 693 - 707.
[Abstract] [Full Text] [PDF]


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