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Keith May, Robert Hess; Ladder contours are undetectable in the periphery. Journal of Vision 2007;7(9):113. doi: 10.1167/7.9.113.
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© 2017 Association for Research in Vision and Ophthalmology.
In many studies of contour integration, the task is to detect a contour consisting of spatially separated Gabor elements positioned along a smooth path (e.g., Field, Hayes, & Hess, 1993, Vision Research, 33, 173–193). The elements can be aligned with the path (“snakes”) or perpendicular to it (“ladders”). With foveal viewing, ladders are generally harder to detect than snakes but, as long as they are fairly straight, ladders can still be detected quite easily. We found a striking deficit in detection of ladders in the periphery. Completely straight ladders were undetectable at an eccentricity of 6 degrees of visual angle, whereas performance on straight snakes at this eccentricity was at or close to 100%. This suggests that ladder detection is disproportionately impaired in the periphery, but an alternative explanation is that there is a general impairment of ladder detection that only shows up in the periphery, where performance falls away from ceiling. To address this issue, we brought performance away from ceiling in the fovea by jittering the orientations of the elements. For two subjects, foveal performance was matched for snakes and ladders with the same orientation jitter levels. In both cases, detection of ladders fell to chance at an eccentricity of 4 deg, whereas detection of snakes remained significantly above chance up to and including the largest eccentricity that we tested (8 deg). The failure to detect ladders at such small eccentricities may partly explain the relative difficulty in detecting ladders that has been reported in previous studies: in all of these studies, the position of the contour has been randomized to some extent. The difference in the effect of eccentric viewing on snakes and ladders means that any positional randomization would have caused a greater disruption to detection of ladders.
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