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Barbara Dillenburger, Christian Wehrhahn; Real line masks “close the gap” in abutting line type illusory contour processing. Journal of Vision 2006;6(6):330. doi: 10.1167/6.6.330.
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© ARVO (1962-2015); The Authors (2016-present)
Contextually induced illusory contours (ICs) allow us to perceive objects that are partly occluded or invisible due to poor contrast. Real contours (RCs) can not only induce, but also mask ICs. These interactions possibly reside in areas V1 and V2. How can RCs interfere with IC processing? Masking of abutting line IC induction by real lines might be either due to metacontrast masking of the inducing RCs or to inhibition of endstopped cells hypothetized to induce abutting line ICs.
We tested this by measuring orientation discrimination thresholds of abutting line type ICs in a backward masking paradigm. Masking line patterns (continuous “RCmask”, or abutting “ICmask”) were oriented parallel or at angles −45, 45, or 90deg to the inducing line pattern.
Masking effects depend on the processes mediating masking. If metacontrast masking interferes with inducing RCs, both RCmask and ICmask should interfere. If, however, inhibition of endstopped cells mediates interference with the IC, ICmasks should interfere less than Rcmasks.
We found that ICmasks oriented different to the inducers interfered stronger than corresponding RCmasks, indicating metacontrast masking of ICs. ICmasks parallel to the inducers, however, showed decreased masking in comparison to RCmasks.
Our data show, first, the masking of an IC by another parallel IC comparable to RC metacontrast masking. Second, these results suggest that RCmasks parallel to the inducers inhibit endstopped cells, thus “close the gap”, rather than metacontrast mask inducing lines. This is consistent with the hypothesis that endstopped cells induce abutting line type ICs.
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