Vernier acuity

With a large number of receptive channels, the human visual system processes information in a parallel fashion. A single glimpse acquires a wealth of information the field of view for two eyes is 180° horizontally and 120° vertically (Mehr and Shindell, 1990). The spatial resolution in the central (foveal) part of the visual field is approximately 0.5-1.0 min of arc (Shlaer, 1937), although Vernier acuity, the specialized task of detecting a misalignment of two lines placed end to end, is much finer, approximately 2 s of arc (Stigmar, 1970). Low-contrast presentations substantially reduce visual acuity. 

Stigmar, G. 1970. Observation on vernier and stereo acuity with special reference to their relationship. Acta Ophthalmol. 48 979. 

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