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Cerebral Cortex Advance Access published online on August 28, 2008
Cerebral Cortex, doi:10.1093/cercor/bhn139
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© The Author 2008. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

The Center-Surround Profile of the Focus of Attention Arises from Recurrent Processing in Visual Cortex

C. N. Boehler1, J. K. Tsotsos2, M. A. Schoenfeld1,3,4, H.-J. Heinze1,2 and J.-M. Hopf1,2

1 Leibniz-Institute for Neurobiology, D-39118 Magdeburg, Germany, 2 Centre for Vision Research and Department of Computer Science and Engineering, York University, Toronto, Ontario M3J 1P3, Canada, 3 Department of Neurology II, Otto-von-Guericke-University of Magdeburg, D-39120 Magdeburg, Germany, 4 Kliniken Schmieder, D-78476 Allensbach, Germany

Address correspondence to Jens-Max Hopf, MD, Department of Neurology II, Otto-von-Guericke-University of Magdeburg, Leipziger Strasse 44, D-39120 Magdeburg, Germany. Email: jens-max.hopf{at}medizin.uni-magdeburg.de.

We recently demonstrated with magnetoencephalographic recordings in human observers that the focus of attention in visual search has a spatial profile consisting of a center enhancement surrounded by a narrow zone of sensory attenuation. Here, we report new data from 2 experiments providing insights into the cortical processes that cause the surround attenuation. We show that surround suppression appears in search tasks that require spatial scrutiny, that is the precise binding of search-relevant features at the target's location but not in tasks that permit target discrimination without precise localization. Furthermore, we demonstrate that surround attenuation is linked with a stronger recurrent activity modulation in early visual cortex. Finally, we show that surround suppression appears with a delay (more than 175 ms) that is beyond the time course of the initial feedforward sweep of processing in the visual system. These observations together indicate that the suppressive surround is associated with recurrent processing and binding in the visual cortex.

Key Words: human • magnetoencephalography • spatial • suppression • visual attention


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