THE POGGENDORFF ILLUSION WITH ANOMALOUS SURFACES: MANAGING PAC-MANS, PARALLELS LENGTH AND TYPE OF TRANSVERSAL.
In the classical Poggendorff illusion, a rectangular surface partially occludes an oblique line, and it lead to perceive as misaligned the two ends of the line segment, when, in fact, they are aligned. The illusion persists when the obscuring rectangle is replaced by Kanizsa-like subjective contours (Tibber et al. 2008) and when both the rectangle and oblique segments consist of Pac-Man tokens, generating Kanizsa-like subjective contours (Spoto et al., 2008). Nevertheless, previous research did not completely clarify the role of the presence of Pac- Man tokens in generating the effect. In the present research, using the adjustment method, the role of the mere presence of the Pac-Mans is further investigated, comparing three kinds of configurations: Pac-Mans generating surface, rotated Pac-Mans and no Pac-Mans, with two surface sizes and two types of oblique segment (classical line-dot and illusory line). Main results show that an overall effect of the mere presence of Pac-Man induces a sort of anchor in the perceived effect; moreover, we found an illusory effect even in the â€œNo Pac-Manâ€ condition, opening a new issue to be addressed by research in this field.