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D. Zur, S. Ullman; Measuring and modeling filling-in effects in retinal AMD scotomas. Journal of Vision 2002;2(7):183. doi: 10.1167/2.7.183.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal scotomas, caused by Age-Related Macular Degeneration (AMD), often damage the center of the visual field, the locus of high acuity, normally used for the detection and recognition of shapes. As a result of the scotomas, the input image is disrupted at the retina level, but the perceived image usually appears continuous, and at the same time distorted in certain ways. Perceptual filling-in phenomena were studied in the past in relation to the blind spot and to artificial scotomas, but not in relation to the large and central scotomas that characterize AMD patients.
In this study we modeled the perceptual effects associated with retinal AMD scotomas. First, we empirically presented to patients a variety of specially designed patterns at controlled locations, and the patients responses were collected and analyzed. Second, we implemented a mathematical model and computer simulation of the observed filling-in phenomena. The model was based in part on neurophysiological evidence regarding receptive field expansion at the level of V1 in and around the scotomas regions. Psychophysically, we found that 1-D patterns such as lines and gratings were completed across large scotomas (up to 7 deg). Gratings completion was better than that of single line and increased with frequency up to 6.28 c/deg. For 2-D patterns, we found completion of dot arrays that improved with density and regularity. Computationally, we found that simulating the filling-in effect by convoluting the image with an adaptive local filter, that simulates the effect of receptive field expansion, achieves good image restoration of highly damaged images, and can account for many of the observed phenomena. The results suggest that the filling-in occurs at several levels of the visual pathway, that together can compensate for large and dense scotomas, and obtain filling-in of both simple and complex patterns.
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