Journal of Neuroscience, Vol 7, 2601-2617, Copyright © 1987 by Society for Neuroscience
On the role of cortical area V4 in the discrimination of hue and pattern in macaque monkeys
CA Heywood and A Cowey
Cortical visual area V4 in macaque monkeys has a large proportion of
neurons that are sensitive to the wavelength or to the color of light. We
tested its role in hue discrimination by removing it in macaque monkeys
trained to discriminate small differences in hue. Hue discrimination
thresholds were permanently elevated in 4 macaque monkeys in which V4 was
removed bilaterally. In contrast, there was no impairment in achromatic
intensity thresholds tested in an identical manner. However, the
discrimination of pattern and orientation was also conspicuously impaired,
indicating that area V4 is not concerned solely with processing information
about wavelength. The multiple defect is consistent with evidence that V4
provides the major cortical visual input to the temporal lobe, where a
large range of visual properties is registered. The performance of monkeys
with V4 ablation was compared with that of unoperated control monkeys and
monkeys with removal of cortex in the banks and floor of the rostral
superior temporal sulcus (STS). Removal of STS had only slight effects on
pattern discrimination and none of hue discrimination. To control for the
possible effects of inadvertent damage to the visual radiations when
removing V4, the lateral striate cortex was partially ablated bilaterally
in a control monkey. This had no effect on any discrimination, despite
producing more retrograde damage to the lateral geniculate nuclei than in
any monkey with V4 ablation. The visual disorder following removal of
visual area V4 strikingly resembles the clinical disorder of mild cerebral
achromatopsia with associated apperceptive agnosia for objects and
patterns.
