FMRI evidence for perceptual filling-in in patients with macular dystrophy M Goldhacker1, K Rosengarth1, S Anstis2, A-M Wirth1, T Plank1, M W Greenlee1 |
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1Institute for Experimental Psychology, Universität Regensburg, Germany |
| Patients with macular dystrophy often report that they are unaware of their central scotoma, suggesting the presence of perceptual filling-in. We used functional Magnetic Resonance Imaging (3 Tesla fMRI) to determine possible neural correlates of perceptual filling-in in patients with retinal dystrophy and central scotomata in both eyes. Fixation behaviour and perimetry were measured with a Nidek microperimeter. We stimulated the central visual field (30°) with low spatial frequency, squarewave gratings with three orientations (10°, 70°, 130°) that were either a) continuous, or b) were interrupted by a central grey disk. The disk was either slightly larger than the scotoma (detectable on 75% of trials) or slightly smaller (detectable on 25% of trials). To control for attention participants responded in a one-back task with respect to the grating orientation. Results indicate that patients exhibit fMRI signal increases in retinotopic visual cortex and these signals were higher during filling-in (no disk: 0.08 %SC, small disk: 0.09 %SC, large disk: 0.02 %SC), and that classification in the foveal projection zone is above chance levels. Ongoing SVM analysis suggests higher classification rates in the foveal projection zone during filling-in conditions. |
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