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The Journal of Neuroscience, August 4, 2004, 24(31):6898-6903; doi:10.1523/JNEUROSCI.1996-04.2004

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BRIEF COMMUNICATION
Setting Boundaries: Brain Dynamics of Modal and Amodal Illusory Shape Completion in Humans

Micah M. Murray,^1,2 Deirdre M. Foxe,² Daniel C. Javitt,² and John J. Foxe^2,3

¹The Functional Electrical Neuroimaging Laboratory, Neuropsychology Division and Radiodiagnostic and Interventional Radiology Service, Vaudois Univerity Hospital Center, Nestlé Hospital, 1011 Lausanne, Switzerland, ²The Cognitive Neurophysiology Laboratory, Program in Cognitive Neuroscience and Schizophrenia, The Nathan S. Kline Institute for Psychiatric Research, Orangeburg, New York 10962, and ³Departments of Neuroscience and Psychiatry, Albert Einstein College of Medicine, Bronx, New York 10462

Normal visual perception requires differentiating foreground from background objects. Differences in physical attributes sometimes determine this relationship. Often such differences must instead be inferred, as when two objects or their parts have the same luminance. Modal completion refers to such perceptual "filling-in" of object borders that are accompanied by concurrent brightness enhancement, in turn termed illusory contours (ICs). Amodal completion is filling-in without concurrent brightness enhancement. Presently there are controversies regarding whether both completion processes use a common neural mechanism and whether perceptual filling-in is a bottom-up, feedforward process initiating at the lowest levels of the cortical visual pathway or commences at higher-tier regions. We previously examined modal completion (Murray et al., 2002) and provided evidence that the earliest modal IC sensitivity occurs within higher-tier object recognition areas of the lateral occipital complex (LOC). We further proposed that previous observations of IC sensitivity in lower-tier regions likely reflect feedback modulation from the LOC. The present study tested these proposals, examining the commonality between modal and amodal completion mechanisms with high-density electrical mapping, spatiotemporal topographic analyses, and the local autoregressive average distributed linear inverse source estimation. A common initial mechanism for both types of completion processes (140 msec) that manifested as a modulation in response strength within higher-tier visual areas, including the LOC and parietal structures, is demonstrated, whereas differential mechanisms were evident only at a subsequent time period (240 msec), with amodal completion relying on continued strong responses in these structures.

Key words: illusory contour; visual evoked potential; VEP; event-related potential; ERP; source analysis; binding; figure-ground segregation

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Received April 1, 2004; revised June 21, 2004; accepted June 22, 2004.

This article has been cited by other articles:

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