Effect of Shape on the Magnitude of the Delboeuf Illusion

Abstract

Three experiments to discuss the applicability of the contour attraction and the parallel attraction to different shapes in the Delboeuf illusion. The contour attraction suggests that the contours of the test figure and the inducer have an effect of interattraction in the Delboeuf illusion, and the parallel attraction suggests that the attraction between non-intersecting contours was maximal when they were parallel. In Experiment 1, the shape of the test figures and the inducers changed simultaneously and formed parallel lines. In Experiment 2, the test figures remained circles while the inducers changed shape. Experiment 3 was identical to Experiment 2 except that the areas of the inducers remained equal. The results demonstrated that the illusion is influenced by shape. Importantly, the effect of shape on the magnitude of the Delboeuf illusion is based on the contour attraction and the parallel attraction. Configurations with circles or shapes more similar to a circle were related more to the contour attraction, whereas shapes that were dissimilar to a circle were related more to the parallel attraction. We suggest that the contour attraction may be a circular modality of the parallel attraction.

Methodological Challenges in the Assessment of Dogs' (Canis lupus familiaris) Susceptibility of the Ebbinghaus-Titchener Illusion Using the Spontaneous Choice Task

“…When presented together, humans perceive a size difference between the target circles, underestimating the target enclosed by the larger inducer ring and overestimating the target enclosed by the smaller inducer ring (Parrish, 2020). While typically illustrated with circles and inducer rings, the Delboeuf illusion can also be presented with any equally sized shapes or objects on two differently sized backgrounds (Howard et al, 2017;Li et al, 2020), though the shape used affects the strength of the illusion (Li et al, 2020). The Ebbinghaus-Titchener illusion also consists of two identically sized target circles surrounded by differently sized inducers.…”