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Donald I. A. MacLeod, I. Fine; Vision after early blindness. Journal of Vision 2001;1(3):470. doi: 10.1167/1.3.470.
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© ARVO (1962-2015); The Authors (2016-present)
We report on the initial visual experiences of MM, who recently received his first successful corneal transplant after becoming completely blind (except for light sensitivity) at age 3. He had no visual imagery or memories of life as a sighted person. MM's post-operative vision presently remains neurally limited, his resolution limit is approximately 1.5 c/deg for static gratings. His perception of depth and 3D spatial arrangement is somewhat rudimentary. He shows interesting differences between the effectiveness of various depth cues: he can exploit occlusion, but not perspective cues or shading (a simulated ball lit from above looks flat). He is impressively free from illusions associated with a suggestion of depth: he matches the images of the Shepard tables veridically, and shows little or no phenomenal regression to the real object in his assessment of the retinal aspect ratio of an images' slanted surface. MM seems to be able to exploit only those cues for depth perception that have counterparts in the tactile world. MM experiences brightness illusions associated with T-junctions (e.g. White's illusion), and he shows roughly normal susceptibility to many geometrical illusions, including Muller-Lyer and Sander illusions. MM's susceptibility to the Muller-Lyer illusion, unlike Gregory and Wallace's SB, suggests that this illusion does not depend on processes associated with depth perception. Motion is particularly efficacious in MM's visual world. He is almost twice as sensitive to moving gratings as to stationary gratings. He was able to recognize a simple Johansson point light figure as depicting a moving person. He does not perceive subjective contours in static displays, but does if the display elements are set in motion. He cannot recognize a stationary wire frame cube, but can when it is rotated as a KDE stimulus. These results suggest that motion mechanisms may be more robust to deprivation, or perhaps are sustained in the blind by tactile experience.
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