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Characterisation of the misalignment and misangulation components in the Poggendorff and corner-Poggendorff illusions

Reports the results of a component analysis of the Poggendorff illusion (PI) and several of its variants, including in particular the "corner-Poggendorff" illusion, and variants with a single arm. Using a nulling method, an orientation profile of each configuration was determined. A pure-misalignment component (MLC) and a pure misangulation component (MAC) of constant sign, having peaks at the orientations of the arms were identified. Both were present in both the classic and the corner-Poggendorff configurations. Thus, the MLC appears clearly in the classic PI, once the MAC is partitioned out. Similarly, the corner-Poggendorff configuration, which essentially estimates a MLC, contains a MAC component which becomes apparent once the MAC is nulled. While the analysis accounts for much of the variability in the shapes of the profiles, additional assumptions must be made to explain the relatively small MAC measured in the corner Poggendorff configuration, and the relatively large illusion measured in the configurations with a single arm. The authors suggest that parallelism and colinearity detectors provide counteracting cues, the 1st class reducing MAC corner-Poggendorff configuration, and the 2nd class reducing the illusion in the Poggendorff configurations with 2 arms. (PsycINFO Database Record (c) 2005 APA, all rights reserved)



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