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Uri Polat, Yoram Bonneh, Dov Sagi; Lateral interactions and crowding in amblyopia. Journal of Vision 2003;3(9):342. doi: 10.1167/3.9.342.
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© ARVO (1962-2015); The Authors (2016-present)
Perceptual crowding is a strong phenomenon in which visual acuity for a single pattern degrades significantly when surrounded by other similar patterns. In amblyopic vision, it could be observed at fixation, extending over long distances. We investigated the relation between crowding and lateral interactions, in a group of anisometropic (N=7) and strabismic (or combined) (N=9) amblyopic patients using four different paradigms: (1) A single and multi-pattern (crowded) computerized E-test, (2) Vernier acuity of lines and Gabor patches with lateral flankers, (3) Orientation discrimination of lines and Gabor patches with lateral flankers and (4) Contrast detection of Gabor patches with lateral flankers (lateral masking). To isolate low-level lateral interactions from higher-level selection mechanisms, we added color to the target pattern (for lines only, not for Gabor paradigms), which made it distinguishable from its surround. We found that the strabismic (and combined) patients with amblyopia had a strong crowding effect in all four paradigms and that this effect decreased to half with the introduction of color (for line patterns). The anisometropic amblyopes had a very small crowding effect, which could not be removed with color. Both groups showed lateral suppression of flankers for contrast detection, but the suppression for the strabismic patients was much stronger and extended a larger distance (over 6 wave lengths; confirmed in a large patient sample, N=80). These results suggest that crowding in amblyopia involves two main components: (1) suppressive lateral interactions, and (2) impaired selectivity or attentional access which could be removed with proper tagging (e.g. color). While patients with strabismus show both components, anisometropic patients show only low lateral suppression and little crowding.
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