About specific and general factors for visual illusions

Contrary to studies of audition and cognition, we previously did not find evidence for a general common factor for vision but for many very specific ones. For example, we found strong correlations between 19 versions of the Ebbinghaus illusion, which differed in color, shape, size or texture (N=87), suggesting a factor specific for the Ebbinghaus illusion. However, the Ebbinghaus illusion correlated very little with other illusions. Here, we tested whether illusion perception is orientation specific, similar to perceptual learning. We tested 5 illusions with 4 different orientations (N=20). While we found almost no inter-illusory correlations, most intra-illusory correlations were significant, i.e., susceptibility to an illusion does not seem to depend on its orientation. Contrary to perceptual learning, this finding provides further evidence for illusion-specific factors but not stimulus specific factors.\ The project was funded by Swiss National Science Foundation (SNSF), project "Learning from Delayed and Sparse Feedback" (CRSII2_147636).