Journal of Neuroscience, Vol 9, 776-783, Copyright © 1989 by Society for Neuroscience
Chromatic and achromatic vision of macaques: role of the P pathway
WH Merigan
Department of Ophthalmology, University of Rochester Medical Center, New York 14642.
Chromatic and achromatic contrast sensitivity were measured in a human
observer, 2 normal macaque monkeys, and 3 monkeys with severe toxicant-
induced damage to the parvocellular projecting retinogeniculate pathway (P
cell-deficient monkeys). Damage to the P pathway was produced by the oral
administration of acrylamide monomer (Eskin and Merigan, 1986). Contrast
sensitivity was measured in all subjects with isochromatic luminance
gratings, as well as isoluminant chromatic gratings, modulated along
several directions of a color space that represents color-opponent and
luminance contrast (Krauskopf et al., 1986). The chromatic and achromatic
sensitivity of the control monkeys was virtually identical to that of the
human observer. Chromatic sensitivity of the P cell-deficient monkeys,
measured at a low spatial frequency (0.3 c/deg), along a constant-blue
color axis, was 0.9-1.5 log units lower than that of controls. Similar
losses were seen along a tritanopic confusion axis and along 2 intermediate
axes of color direction. Chromatic thresholds measured at higher spatial
frequency (2.0 c/deg) were similarly reduced. Counterphase-modulated
chromatic gratings were used to test color sensitivity over a range of
temporal frequencies up to 15 Hz, and the loss of color vision was
substantial over the entire range of frequencies. The luminance contrast
sensitivity of the P cell-deficient monkeys for stationary gratings
decreased after exposure by 0.5-0.8 log units. These results indicate that
the chromatic and achromatic spatial vision of macaques is very similar to
that of humans. They also suggest that the P pathway plays an important
role in macaque chromatic sensitivity at all spatial frequencies, as well
as achromatic sensitivity at high spatial and lower temporal frequencies.