Residual target detection as a function of stimulus size.

In the visual field defects of 5 patients with damage in the postgeniculate part of the primary visual system, residual detectability of an achromatic intensity target was tested as a function of target diameter, which was 10, 27, 44, 69 and 116 min of arc of visual angle. The set of 5 targets was presented at 3 different intensity ranges on a background of low photopic luminance. Within this size range residual detectability was a V-shaped function of target size with a dip at 44 min of arc. This result is discussed in relation to the centre/surround organization of receptive and perceptive fields.