Color, orientation and cytochrome oxidase reactivity in areas V1, V2 and V4 of macaque monkey visual cortex.

Color and orientation processing in the macaque monkey first segregates into cytochrome oxidase (CO)-rich blobs and -poor interblobs of area V1, from where the two streams flow through areas V2 and V4. This parallel representation is believed to enhance processing speed by compartmentalizing tasks of similar kinds, though our knowledge of the mechanisms is still elementary. We have examined the interaction and separation of color and orientation processing in neurons (n = 569) of the macaque visual cortex (V1, V2, V4) on the basis of microelectrode recordings. In all three areas, neurons selective for midspectral (MS) colors (e.g., yellow, green) were also found to be more orientation selective than those preferring endspectral (ES) colors (e.g., blue, red). The majority of achromatic (AC) cells responsive to bright stimuli were also orientation selective. When locations of cells and penetration columns were correlated with cytochrome oxidase (CO) landmarks in V1 and V2, V1 interblob and V2 interstripe cells were found to be predominantly midspectral and oriented, while V1 blob and V2 thin stripe cells were found to be predominantly endspectral and non-oriented. Cells preferring dark colors were found to cluster in thick stripes in V2, and in columns in V4. Separate clustering of midspectral (MS) and endspectral (ES) systems in V4 was also noted. With the results shown in a companion paper (Behav. Brain Res., 76 (1996) 51-70), the present data indicate that the visual system appears to optimize color and spatial acuity by separating chromatic information into non-oriented endspectral and oriented midspectral components.