We used qualitative tests to assess the sensitivity of 1043
V2 neurons (predominantly multiunits) in anesthetised macaque
monkeys to direction, length, orientation, and color of moving
bar stimuli. Spectral sensitivity was additionally tested by
noting ON or OFF responses to flashed stimuli of varied size
and color. The location of 649 units was identified with respect
to cycles of cytochrome oxidase stripes (thick-inter-thin-inter)
and cortical layer. We used an initial 8-way stripe classification
(4 stripes, and 4 “marginal” zones at interstripes
boundaries), and a 9-way layer classification (5 standard layers
(2–6), and 4 “marginal” strata at layer
boundaries). These classes were collapsed differently for
particular analyses of functional distribution; the main
stripe-by-layer analysis was performed on 18 compartments (3
stripes × 6 layers). We found direction sensitivity only
within thick stripes, orientation sensitivity mainly in thick
stripes and interstripes, and spectral sensitivity mainly in
thin stripes. Positive length summation was relatively more
frequent in thick stripes and interstripes, and negative
length/size summation in thin stripes. All these
“majority” characteristics of stripes were most
prominent in layers 3A and 3B. By contrast, “minority”
characteristics (e.g. spectral sensitivity in thick stripes;
positive size summation in thin stripes) tended to be most frequent
in the outer layers, that is, layers 2 and 6. In consequence,
going by the four functions tested, the distinctions between
stripes were maximal in layer 3, moderate in layer 2, and minimal
in layer 6.
The functional organization of area V2, I: Specialization
across stripes and layers