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Cerebral Cortex Advance Access originally published online on January 19, 2009
Cerebral Cortex 2009 19(10):2230-2239; doi:10.1093/cercor/bhn243
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© The Author 2009. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Feature Binding in the Feedback Layers of Area V2

Stewart Shipp1,2, Daniel L. Adams3, Konstantinos Moutoussis4 and Semir Zeki1

1 Laboratory of Neurobiology, Department of Cell and Developmental Biology, University College London, London WC1E 6BT, UK, 2 Institute of Ophthalmology, University College London, London EC1V 9EL, UK, 3 Center for Mind/Brain Science, University of Trento, Trento TN 38100, Italy, 4 Department of Philosophy and History of Science, University of Athens, 157 71 Athens, Greece

Address correspondence to email: s.shipp{at}ucl.ac.uk.

The visual features of an object are processed by multiple, functionally specialized areas of cerebral cortex. When several objects are seen simultaneously, what mechanism preserves the association of features that belong to a single item? We address this question—known as the "binding problem"—by examining combinatorial feature selectivity of neurons in area V2. In recording from anesthetized macaques, we estimate that dual selectivity for chromatic and spatiotemporal attributes is 50% more common (27% vs. 18% sampling frequency) in superficial and deep layer neurons receiving feedback connections from higher areas, compared with layer 4-3 neurons relaying ascending signals. The operation of feedback pathways is thought to mediate attentional modulation of activity that may achieve binding through acting to select one single object for higher representation and filtering out competing objects. We propose that dual-selective neurons perform a "bridging" function, mediating the transfer of feedback-induced bias between feature dimensions. The bias can be propagated through V2 output neurons (of unitary selectivity) to higher levels of specialized processing and so promote selection of the target object's representation among multiple feature maps. The bridging function would thus act to unify the outcome of parallel, object-selective processes taking place along segregated visual pathways.

Key Words: cerebral cortex • dual selectivity • laminar circuitry • macaque monkey • neurophysiology • vision


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