Linearly Additive Shape and Color Signals in Monkey Inferotemporal Cortex

• Published in: Journal of neurophysiology 2009-04, Vol.101 (4), p.1867-1875
• Main Authors: McMahon, David B. T, Olson, Carl R
• Format: Article
• Language: English
• Subjects: Action Potentials - physiology; Animals; Color Perception - physiology; Discrimination, Psychological - physiology; Female; Linear Models; Macaca mulatta; Male; Neurons - classification; Neurons - physiology; Pattern Recognition, Visual - physiology; Photic Stimulation - methods; Reaction Time - physiology; Temporal Lobe - cytology; Temporal Lobe - physiology; Visual Pathways - physiology
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.90650.2008

Center for the Neural Basis of Cognition, Mellon Institute, and Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania Submitted 19 June 2008; accepted in final form 8 January 2009 How does the brain represent a red circle? One possibility is that there is a specialized and possibly time-consuming process whereby the attributes of shape and color, carried by separate populations of neurons in low-order visual cortex, are bound together into a unitary neural representation. Another possibility is that neurons in high-order visual cortex are selective, by virtue of their bottom-up input from low-order visual areas, for particular conjunctions of shape and color. A third possibility is that they simply sum shape and color signals linearly. We tested these ideas by measuring the responses of inferotemporal cortex neurons to sets of stimuli in which two attributes—shape and color—varied independently. We find that a few neurons exhibit conjunction selectivity but that in most neurons the influences of shape and color sum linearly. Contrary to the idea of conjunction coding, few neurons respond selectively to a particular combination of shape and color. Contrary to the idea that binding requires time, conjunction signals, when present, occur as early as feature signals. We argue that neither conjunction selectivity nor a specialized feature binding process is necessary for the effective representation of shape–color combinations. Address for reprint requests and other correspondence: D.B.T. McMahon, Laboratory of Neuropsychology, National Institute of Mental Health, NIH, 49 Convent Drive, Room B2-J45, Bethesda, MD 20892 (E-mail: mcmahond{at}mail.nih.gov )