Jl. Gallant et al., NEURAL ACTIVITY IN AREAS V1, V2 AND V4 DURING FREE VIEWING OF NATURALSCENES COMPARED TO CONTROLLED VIEWING, NeuroReport, 9(1), 1998, pp. 85-90
UNDER natural viewing conditions primates make frequent exploratory ey
e movements across complex scenes. We recorded neural activity of 62 c
ells in visual areas V1, V2 and V4 in an awake behaving monkey that fr
eely viewed natural images. About half of the cells studied showed a m
odulation in firing rate following some of the eye movements made duri
ng free viewing, though the proportions showing a discernible modulati
on varied across areas. These cells were also examined under controlle
d viewing conditions in which gratings or natural image patches were f
lashed in and around the classical receptive field while the animal pe
rformed a fixation task. Activity rates were generally highest with fl
ashed gratings and lowest during free viewing. Flashed natural image p
atches evoked responses between these two extremes, and the responses
were higher when the patches were confined to the classical receptive
field than when they extended into the non-classical surround. Thus th
e reduction of activity during free viewing relative to that obtained
with flashed gratings is partly attributable to natural images being l
ess effective stimuli and partly to suppressive spatio-temporal neural
mechanisms that are important during natural vision.