Human brain responses to different image contrasts.
Human brain activity was evoked by a dynamic random-dot display in which a square-wave grating appeared and disappeared at regular intervals. Grating visibility was determined by one of four different contrasts: texture, stereo disparity, luminance, or color. Scalp fields measured with 31 electrodes were used to estimate epicortical potential fields. The estimation procedure required detailed anatomical data for each subject. These were obtained from magnetic resonance images. A three-dimensional digitizer and a stereotactic headgear were used to accurately merge the frame of reference of the magnetic resonance image with that of the evoked potential. Epicortical potential fields provided a better indicator of where brain activity is evoked than did scalp fields. These procedures also corrected for anatomical variations between scalp and brain from subject to subject. In two right-handed female subjects, evoked activity was observed in the left posterior parietal and the right occipital, parieto-occipital and posterior temporal cortices. Evoked activity was observed in the left parietal cortex for luminance processing, in the right parietal cortex for texture processing and in the right temporal cortex for color processing, which was selective for the particular contrast.
Srebro
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Department of Ophthalmology, University of Texas Southwestern Medical Center at Dallas 75235-8592.
Oguz
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RM
Purdy
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PD
D001921:Brain / Q000502:physiology*; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000502:physiology; D003118:Color Perception / Q000502:physiology; D015350:Contrast Sensitivity / Q000502:physiology; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D008027:Light; D008279:Magnetic Resonance Imaging; D010364:Pattern Recognition, Visual / Q000502:physiology*; D012535:Scalp / Q000502:physiology; D015357:Vision Disparity / Q000502:physiology