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Daniel D. Dilks, Michael McCloskey; The El Greco effect: Perceptual distortion from visual cortical reorganization. Journal of Vision 2005;5(8):901. doi: 10.1167/5.8.901.
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© ARVO (1962-2015); The Authors (2016-present)
Cortical reorganization resulting from loss of sensory input (e.g., digit amputation, retinal lesions) has been studied extensively in the somatosensory system and to a lesser extent in the visual system. However, little work has considered the perceptual consequences of cortical reorganization. We present evidence from stroke patient BL, who has a damage to right-hemisphere inferior optic radiations. The damage caused a loss of sensory input to primary visual cortex representing the upper left visual field (LVF), producing a left superior homonymous quadrantanopia (i.e., blindness in the left upper quadrant). However, primary visual cortex itself is intact. BL exhibits dramatic distortion of perceived shape for stimuli in the lower LVF: The stimuli appear vertically elongated (toward and into the blind upper quadrant). For example, when shown a circle, he reports a “cigar” extending upward. Psychophysical testing confirmed that the distortion selectively affects the vertical dimension of shapes (i.e., the height); judgments concerning the horizontal dimension (width) are intact. Additional experiments revealed that the deficit is selective to vision (i.e., tactile shape judgments are intact); that vertical distance as well as shape judgments are affected; that the vertical distortion arises in a retinocentric frame of reference; that the extent of vertical distortion monotonically decreases with distance from the blind quadrant; and that deficit affects not only vision-for-perception, but also vision-for-action (grip aperture). Taken together, these results support the hypothesis that BL's perceptual distortions result from cortical reorganization in the early visual system: Visual cortex deprived of input from the upper LVF has apparently become responsive to stimuli in the lower LVF. These results have implications for understanding the nature and perceptual consequences of cortical reorganization in the human visual system.
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