[Effect of defocusing a visual stimulus on a human evoked potential].

A study was made of EP recorded in the visual projection area of the cerebral cortex in children with normal sight and in those with disturbed refraction when presented with blank and checkered patterns, the dimensions of the chess squares equalling 10, 20, 40, 60 and 120 angular minutes. In children with normal sight the patterns were defocussed by eyeglass lenses of --1 to +/- 6 dioptries. The investigation revealed a different EP configuration on the presentation of blank and checkered patterns. There was a similarity between the EP change when a blank pattern was replaced by a checkered one, and when the checkered pattern was made sharper. It is assumed that these EP changes results from enhanced lateral inhibition due to the contrast boundaries of the checkered pattern, The experiments carried out on children with disturbed refraction indicated that the maximal EP amplitude corresponded to the optimal optic correction, which shows that theuse of EP is a promising cue in determing vision acuity.