Visual symmetry perception in early onset monocular blindness

Symmetry detection is impaired by abnormal binocular vision development such as in amblyopia. However, the detection of symmetry has never been investigated in cases where input from one eye is profoundly compromised. Testing monocularly blind (MB) individuals represents a unique opportunity to investigate whether symmetry salience relies on a normally developed binocular visual system. In a visual symmetry detection task using dot patterns, congenitally MB showed comparable accuracy to normally sighted individuals viewing monocularly. This included better detection of vertically than horizontally symmetric patterns. However, the MB were slower than controls in detecting a symmetrical pattern. In a control target-detection task, no significant differences in performance were observed between these groups. Overall, normal developing binocular vision does not appear necessary for the visual system to detect the presence of visual symmetry. However, optimal detection mechanisms may be dependent on binocular summation or other processes dependent on input from both eyes