Illusory contours over pathological retinal scotomas

• Published in: PloS one Vol. 6; no. 10; p. e26154
• Main Authors: De Stefani, Elisa, Pinello, Luisa, Campana, Gianluca, Mazzarolo, Monica, Lo Giudice, Giuseppe, Casco, Clara
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 12.10.2011; Public Library of Science (PLoS)
• Subjects: Adolescent; Biology; Blindness; Contours; Contrast Sensitivity - physiology; Curvature; Discrimination; Female; Form Perception - physiology; Frequency dependence; Humans; Illusions; Illusions - physiology; Macula Lutea - pathology; Macula Lutea - physiopathology; Macular degeneration; Macular Degeneration - congenital; Macular Degeneration - pathology; Macular Degeneration - physiopathology; Male; Medicine; Neural coding; NMR; Nuclear magnetic resonance; Optic nerve; Photic Stimulation; Photoreceptors; Physiological aspects; Physiology; Retina; Retina - pathology; Retina - physiopathology; Scotoma - pathology; Scotoma - physiopathology; Social and Behavioral Sciences; Studies; Visual cortex; Visual discrimination; Visual perception; Visual stimuli; Visual task performance
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0026154

Our visual percepts are not fully determined by physical stimulus inputs. Thus, in visual illusions such as the Kanizsa figure, inducers presented at the corners allow one to perceive the bounding contours of the figure in the absence of luminance-defined borders. We examined the discrimination of the curvature of these illusory contours that pass across retinal scotomas caused by macular degeneration. In contrast with previous studies with normal-sighted subjects that showed no perception of these illusory contours in the region of physiological scotomas at the optic nerve head, we demonstrated perfect discrimination of the curvature of the illusory contours over the pathological retinal scotoma. The illusion occurred despite the large scar around the macular lesion, strongly reducing discrimination of whether the inducer openings were acute or obtuse and suggesting that the coarse information in the inducers (low spatial frequency) sufficed. The result that subjective contours can pass through the pathological retinal scotoma suggests that the visual cortex, despite the loss of bottom-up input, can use low-spatial frequency information from the inducers to form a neural representation of new complex geometrical shapes inside the scotoma.