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The Journal of Neurophysiology Vol. 83 No. 6 June 2000, pp. 3525-3536
Copyright ©2000 by the American Physiological Society
Department of Psychology, Stanford University, Stanford, California 94305-2130
Huk, Alexander C. and
David J. Heeger.
Task-Related Modulation of Visual Cortex. J. Neurophysiol. 83: 3525-3536, 2000. We performed a series
of experiments to quantify the effects of task performance on cortical
activity in early visual areas. Functional magnetic resonance imaging
(fMRI) was used to measure cortical activity in several cortical visual
areas including primary visual cortex (V1) and the MT complex (MT+) as
subjects performed a variety of threshold-level visual psychophysical
tasks. Performing speed, direction, and contrast discrimination tasks
produced strong modulations of cortical activity. For example, one
experiment tested for selective modulations of MT+ activity as subjects
alternated between performing contrast and speed discrimination tasks.
MT+ responses modulated in phase with the periods of time during which subjects performed the speed discrimination task; that is, MT+ activity
was higher during speed discrimination than during contrast discrimination. Task-related modulations were consistent across repeated measurements in each subject; however, significant individual differences were observed between subjects. Together, the results suggest 1) that specific changes in the
cognitive/behavioral state of a subject can exert selective and
reliable modulations of cortical activity in early visual cortex, even
in V1; 2) that there are significant individual
differences in these modulations; and 3) that visual
areas and pathways that are highly sensitive to small changes in a
given stimulus feature (such as contrast or speed) are selectively
modulated during discrimination judgments on that feature. Increasing
the gain of the relevant neuronal signals in this way may improve their
signal-to-noise to help optimize task performance.
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