Spatial Frequency Properties of Contour Interaction in Normal and Amblyopic Vision
Ehrt O.1,2, Hess R. F.1
1McGill Vision Research, Department of Ophthalmology, McGill University, Montréal/CDN; 2Department of Ophthalmology, Ludwig Maximilians University, Muenchen
Purpose: The cortical mechanisms underlying contour interaction (the detrimental effect of flanking structures on the discrimination of optotypes) are still poorly understood. The role of low level mechanisms (e.g. masking) is controversial. We investigated the spatial frequency properties of contour interaction in normal foveal vision to compare them with those of masking and in amblyopes, i.e. subjects who suffer from marked contour interation.
Method: Landolt-Cs with a diameter of 0.5° for normals (n=5) and 0.5° to 2.3° for amblyopes (n=5) and four high contrast flanking bars were digitally filtered and presented for 500 ms on a mid grey background of a calibrated monitor. The contrast threshold for discrimination of the orientation of the Landolt-C were measured for 3 different relative spatial frequencies of the C (0.94 - 3.75 cpl) and up to 14 relative spatial frequencies of the bars (0.47 - 10 cpl).
Results: All subjects showed a sharp tuning curve. In normal foveal vision the spatial frequency of bars with peak interaction increased only slightly from 1.0 to 1.3 cpl when the spatial frequency of the C increased from 0.94 to 3.75 cpl. All amblyopes did show a tuning curve similar to the normal subjects with a peak interaction at a bar frequency
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