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The Journal of Neuroscience, January 3, 2007, 27(1):93-97; doi:10.1523/JNEUROSCI.3162-06.2007

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Brief Communications
The Effect of Spatial Attention on Contrast Response Functions in Human Visual Cortex

Giedrius T. Buracas and Geoffrey M. Boynton

The Salk Institute, La Jolla, California 92037, and Center for Functional MRI, University of California, San Diego, La Jolla, California 92093

Correspondence should be addressed to Giedrius T. Buracas, University of California, San Diego Center for Functional MRI, 9500 Gilman Drive, La Jolla, CA 92093.

Previous electrophysiology data suggests that the modulation of neuronal firing by spatial attention depends on stimulus contrast, which has been described using either a multiplicative gain or a contrast-gain model. Here we measured the effect of spatial attention on contrast responses in humans using functional MRI. To our surprise, we found that the modulation of blood oxygenation level-dependent (BOLD) responses by spatial attention does not greatly depend on stimulus contrast in visual cortical areas tested [V1, V2, V3, and MT+ (middle temporal area)]. An additive model, rather than a multiplicative or contrast-gain model best describes the attentional modulations in V1. This inconsistency with previous single-unit electrophysiological data has implications for the population-based neuronal source of the BOLD signal.

Key words: spatial attention; contrast; fMRI; vision; additive; functional imaging

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Received Feb. 16, 2006; revised Nov. 21, 2006; accepted Nov. 22, 2006.

Correspondence should be addressed to Giedrius T. Buracas, University of California, San Diego Center for Functional MRI, 9500 Gilman Drive, La Jolla, CA 92093.

This article has been cited by other articles:

				X. Li, Z.-L. Lu, B. S. Tjan, B. A. Dosher, and W. Chu Blood oxygenation level-dependent contrast response functions identify mechanisms of covert attention in early visual areas PNAS, April 22, 2008; 105(16): 6202 - 6207. [Abstract] [Full Text] [PDF]

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