ABSTRACT
We investigated some aspects of the cortical processes responsible for contour interaction, i.e. the detrimental effect of flanks on the discrimination of a central optotype. METHODS: Contrast thresholds for detection of the Landolt — C flanked by four high contrast bars and thresholds for discrimination of its orientation were measured for five normal subjects and five amblyopes. RESULTS: Detection thresholds for unfiltered stimuli did not change more than 30% when bars were brought in. Discrimination thresholds showed a much stronger threshold elevation for small stimuli and in amblyopia but not for large stimuli. Spatial frequency properties of contour interaction were unlike those of contrast masking. CONCLUSIONS: Low level contrast masking contributes to physiologic foveal contour interaction only for large stimuli whereas higher level processes seem to be involved in contour interaction for smaller stimuli and in amblyopia.
