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The Journal of Neuroscience, November 15, 2006, 26(46):12043-12054; doi:10.1523/JNEUROSCI.3225-06.2006

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Behavioral/Systems/Cognitive
Boundary Completion Is Automatic and Dissociable from Shape Discrimination

Micah M. Murray,^1,2 Michelle L. Imber,^2,3 Daniel C. Javitt,² and John J. Foxe^2,4

¹Functional Electrical Neuroimaging Laboratory, Neuropsychology Division and Radiology Service, Centre Hospitalier Universitaire Vaudois, Lausanne 1011, Switzerland, ²Cognitive Neurophysiology Laboratory, Program in Cognitive Neuroscience and Schizophrenia, The Nathan S. Kline Institute for Psychiatric Research, Orangeburg, New York 10962, ³Department of Psychology, New York University, New York, New York 10003, and ⁴Program in Cognitive Neuroscience, Department of Psychology, City College of the City University of New York, New York, New York 10031

Correspondence should be addressed to either of the following: Micah M. Murray, The Functional Electrical Neuroimaging Laboratory, Neuropsychology Division, Centre Hospitalier Universitaire Vaudois, Hôpital Nestlé, 5 Avenue Pierre Decker, 1011 Lausanne, Switzerland, Email: micah.murray{at}chuv.ch; or John J. Foxe, The Cognitive Neurophysiology Laboratory, The Nathan S. Kline Institute for Psychiatric Research, 140 Old Orangeburg Road, Orangeburg, NY 10962, Email: foxe{at}nki.rfmh.org

Normal visual perception readily overcomes suboptimal or degraded viewing conditions through perceptual filling-in processes, enhancing object recognition and discrimination abilities. This study used visual evoked potential (VEP) recordings in conjunction with electrical neuroimaging analyses to determine the spatiotemporal brain dynamics of boundary completion and shape discrimination processes in healthy humans performing the so-called "thin/fat" discrimination task (Ringach and Shapley, 1996) with stimuli producing illusory contours. First, results suggest that boundary completion processes occur independent of subjects' accuracy on the discrimination task. Modulation of the VEP to the presence versus absence of illusory contours [the IC effect (Murray et al., 2002)] was indistinguishable in terms of response magnitude and scalp topography over the 124–186 ms poststimulus period, regardless of whether task performance was correct. This suggests that failure on this discrimination task is not primarily a consequence of failed boundary completion. Second, the electrophysiological correlates of thin/fat shape discrimination processes are temporally dissociable from those of boundary completion, occurring during a substantially later phase of processing (330–406 ms). The earlier IC effect was unaffected by whether the perceived contour produced a thin or fat shape. In contrast, later time periods of the VEP modulated according to perceived shape only in the case of stimuli producing illusory contours, but not for control stimuli for which performance was at near-chance levels. Collectively, these data provide further support for a multistage model of object processing under degraded viewing conditions.

Key words: illusory contour; visual evoked potential; VEP; event-related potential; ERP; shape discrimination; object recognition; binding

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Received March 23, 2006; revised Oct. 6, 2006; accepted Oct. 6, 2006.

Correspondence should be addressed to either of the following: Micah M. Murray, The Functional Electrical Neuroimaging Laboratory, Neuropsychology Division, Centre Hospitalier Universitaire Vaudois, Hôpital Nestlé, 5 Avenue Pierre Decker, 1011 Lausanne, Switzerland, Email: micah.murray{at}chuv.ch; or John J. Foxe, The Cognitive Neurophysiology Laboratory, The Nathan S. Kline Institute for Psychiatric Research, 140 Old Orangeburg Road, Orangeburg, NY 10962, Email: foxe{at}nki.rfmh.org

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