Sunday, January 28, 2007

Two's a crowd: suppressed V4 visual responses to sequential stimuli

J. Patrick Mayo

Every minute, we sweep our eyes over
multiple objects. We look at one object
and then another, shifting our gaze across
cluttered scenes when, for example,
searching a desktop for car keys. Such real
world complexities are difficult to model
in the laboratory. Instead, a single stimulus
is often used to characterize visual responses
of neurons, be it a small bar in
primary visual cortex (V1) or a threedimensional
object in “higher” cortical
areas in the inferotemporal (IT) and frontal
lobes. Forays into more complex tasks
using multiple stimuli have mainly been
limited to simultaneously presented stimuli
in search and visual clutter tasks. Remarkably
few studies have investigated
how visual cortices respond to sequential
stimulus presentations. This paucity of research
is surprising given the wealth of
data collected in the psychophysical literature
regarding the temporal phenomena
of visual masking and inhibition of return.
A recent paper in the Journal of Neuroscience
(Motter, 2006) begins to fill this
conceptual void. The author recorded
from visual area V4 in awake behaving
monkeys while long sequences of stimuli
were presented.


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