Hyper-vision of mirror symmetry in patients with macular degenerationreflects parafoveal cortical reorganization.

Purpose: This study aims at comparing participants with juvenile macular degeneration (MD) and normally sighted observers in their sensitivity to mirror and translational symmetry.
Methods: We measured in 25 normal sighted and 9 MD participants sensitivity (d') to detect the symmetry of two dot patterns presented at the opposite sides of their central scotoma.
Results: At a large dot patterns separation (13.3 deg), at which detection failed in normally sighted observers, MD patients had high sensitivity to mirror symmetry, whereas translational symmetry was undetected.
Conclusions: The mirror-translational dissociation is not predicted by the well-known phenomenon of shrinking the location of images surrounding the scotoma. Our results indicate higher capacity of MD with respect to normally sighted observers to organize mirror symmetric dot patterns far apart into a unique percept. Our results suggest that MD have acquired the capability to use information only present in mirror symmetry, i.e., the co-aligned position of the centre of low-frequency filters connecting symmetric dot pairs on opposite sides of the scotoma. This relevant functional change in vision of MD patients may find its explanation in a functionally acquired high-level cortical representation of visual input.