Color signals in human motion-selective cortex.
The neural basis for the effects of color and contrast on perceived speed was examined using functional magnetic resonance imaging (fMRI). Responses to S cone (blue-yellow) and L + M cone (luminance) patterns were measured in area V1 and in the motion area MT+. The MT+ responses were quantitatively similar to perceptual speed judgments of color patterns but not to color detection measures. We also measured cortical motion responses in individuals lacking L and M cone function (S cone monochromats). The S cone monochromats have clear motion-responsive regions in the conventional MT+ position, and their contrast-response functions there have twice the responsivity of S cone contrast-response functions in normal controls. But, their responsivity is far lower than the normals' responsivity to luminance contrast. Thus, the powerful magnocellular input to MT+ is either weak or silent during photopic vision in S cone monochromats.
Wandell
B A
BA
Department of Psychology, Stanford University, California 94305, USA. wandell@stanford.edu
Poirson
A B
AB
Newsome
W T
WT
Baseler
H A
HA
Boynton
G M
GM
Huk
A
A
Gandhi
S
S
Sharpe
L T
LT
D000221:Adaptation, Ocular / Q000502:physiology; D000293:Adolescent; D000328:Adult; D003116:Color; D003118:Color Perception / Q000502:physiology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009039:Motion Perception / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology; D010775:Photic Stimulation; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology; D014793:Visual Cortex / Q000033:anatomy & histology / Q000502:physiology*