Neurophysiological investigations of visual object completion processes
Item
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Title
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Neurophysiological investigations of visual object completion processes
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Identifier
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d_2009_2013:116aab515075:10791
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identifier
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11101
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Creator
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Shpaner, Marina,
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Contributor
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John J. Foxe | Sophie Molholm
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Date
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2011
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Language
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English
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Publisher
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City University of New York.
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Subject
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Neurosciences | Cognitive psychology | contours | ERP | gabors | human | illusory contours | spatial segmentation
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Abstract
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Research over the past several decades has provided exciting insights into the cortical underpinnings of vision. Whereas early efforts concentrated on identifying and characterizing the distinctive properties of neuronal populations, more recent investigations focus on how separate channels of information are integrated. Here, we examined the cortical dynamics of object completion within the framework of interacting parallel pathways. The "frame and fill" model advances fast and coarse scene analysis in the dorsal visual stream as the foundation of more detailed object-related processing in the ventral visual stream. Our first study assesses sensitivity to illusory contour (IC) stimuli within the lateral occipital complex (LOC) as compared to salient region (SR) stimuli, a stimulus class that lacks the classic bounding contours of illusory shapes. Using high-density electrical mapping of visual evoked potentials, we show that early LOC activity is substantially stronger to IC than to SR stimuli, while later LOC activity is stronger to SR than to IC stimuli. We further suggest that crude region based segmentation takes place in the dorsal stream regions prior to contour interpolation. The second study more closely examines contour interpolation in the context of complex visual scenes. We use different levels of clutter to obscure the salience of the centrally presented IC, thus taxing the initial scene delineation process. In support of the "frame-and-fill" model, we show that high levels of clutter significantly affect the early illusory contour sensitivity in the LOC and result in an apparent switch to more effortful mode of contour interpolation. The final study focuses on mechanisms of contour integration in the ventral stream. We arbitrate between two previously advanced mechanisms of contour integration: serial facilitative interactions between collinear cells in the primary visual cortex or pooling of inputs in higher order visual areas. We use retinotopic presentations of Gabor contours embedded in Gabor noise in order to assess the timecourse of earliest cortical activity. We report earliest contour-related cortical responses in the higher-order visual areas and not in the primary visual cortex, indicative of pooling of inputs in extra-striate areas. Overall, the results of our studies support the tenets of the "frame-and-fill" model of cortical processing.
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Type
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dissertation
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Source
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2009_2013.csv
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degree
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Ph.D.
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Program
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Psychology
