SPATIAL-FREQUENCY CHANNELS IN EXPERIMENTALLY STRABISMIC MONKEYS REVEALED BY OBLIQUE MASKING

Although the spatial vision deficits of human strabismic amblyopes hav e been well documented, surprisingly little is known about the mechani sms underlying their visual performance. In an effort to reveal the st ructure underlying the spatial vision deficits associated with strabis mic amblyopia, we measured the performance of monkeys (Macaca nemestri na) with experimental strabismus in a contrast detection task with obl ique masks. The masks were two adjacent identical oblique sine-wave gr atings modulated in space by a Gaussian envelope. The target stimulus was a vertically oriented Gabor patch that appeared superimposed on th e center of either the left or the right mask. The animals were traine d by operant methods to indicate the location of the target. We measur ed detection thresholds in each eye independently for a large number o f test and mask spatial frequencies, For each test spatial frequency, detection thresholds were elevated in the presence of the mask. The th reshold evaluations showed a peak for a particular spatial frequency t hat was typically similar to the test spatial frequency. This pattern of results is consistent with the idea that the tests are detected by a discrete number of channels tuned to a narrow range of spatial frequ encies. The data from the deviated eyes did not appear qualitatively d ifferent from those of the fellow eyes, and could be accounted by the same number of channels in both eyes. Quantitative estimates of the ch annels' characteristics revealed that the channels derived from the de viated eyes' data were similar to those yielded by the fellow eyes, bu t showed a reduction in their sensitivity to contrast.