Kanizsa-like shapes have been widely used to investigate the spatial and temporal properties of
illusory contours and
amodal completion in shape discrimination tasks, and unveil the mechanisms that recover object size, shape, and position from sparsely segregated edge elements.
Kellman & Shipley (1991) described a theory explaining the perception of partly occluded objects and illusory figures, from both static and kinematic information, in a unified framework. However it remained unclear how the cortex implements the visual processing underlying the perception of illusory contours and amodal completion.
Neural responses to illusory contour were found in earlier cortical areas of macaque monkeys like V1, in midlevel visual areas like V4 as well as in higher cortical areas like the inferior temporal cortex (IT) suggesting that the computational power to detect illusory contours and distinguish figure from ground is available early in the visual cortex. However the temporal sequence of the events suggests that this computation involves inter-cortical interaction, and that early perceptual organization is likely to be an interactive process.
Studies using brain imaging techniques like fMRI, MEG, EEG or TMS, have demonstrated since that multiple cortical regions are also activated in the human visual cortex when static or moving Kanizsa-like illusory contours are presented. They showed that both earlier visual areas like V1/V2 and higher-level visual area like LO are critically involved in perceptual completion but with different timing. These results suggest that responses in earlier visual areas may be influenced by top-down modulation from higher areas, which contribute to perceptual completion through neural feedback to V1/V2 areas.
These results may have some clinical implications as schizophrenia patients exhibit abnormal electrophysiological signatures during Kanizsa shape perception tasks. While it remains unclear how these abnormalities are manifested behaviorally and whether they arise from early or late levels in visual processing, a recent study suggests that it is a later conceptually-mediated shape integration stage which is compromised in schizophrenia.
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