The Ebbinghaus Illusion: New Contextual Effects and Theoretical Considerations

Abstract

Current accounts of the Ebbinghaus illusion emphasize either size contrast or contour interaction processes. To assess these alternatives, four variants of the Ebbinghaus figure were constructed using 1, 5, 9, or 13 small circles dispersed along the perimeter of larger contextual circles. 30 observers ranked the perceived size of the central circles and a single control circle. The rankings indicated that increasing the number of small circles reduced the perceived size of the central circle. The results parallel the effects of contextual arcs on the Ebbinghaus illusion and suggest that the mis-estimations of central circle size in Ebbinghaus figures result primarily from contour interactions.

Attractive Contours of the Ebbinghaus Illusion

“…The stimulus set used by Jaeger and Klahs (2015). Panels (a)-(d) show the cards that Jaeger and Klahs (2015) presented to their participants.…”

“…The stimulus set used by Jaeger and Klahs (2015). Panels (a)-(d) show the cards that Jaeger and Klahs (2015) presented to their participants. The cards had 1, 5, 9, or 13 tiny circles located progressively along the perimeter of where the large contextual circles of the more traditional Ebbinghaus figure would appear.…”

“…In a recent study published in Perceptual & Motor Skills, Jaeger and Klahs (2015) created different versions of the Ebbinghaus illusion by gradually adding tiny circles along the edges of where the contextual circles of the traditional Ebbinghaus figure would normally lay (Figure 1a-d). During testing, the participants were provided with four cards, each corresponding to a different version of the Ebbinghaus illusion ( Figure 1a-d), as well as a fifth card consisting of only the inner circle to serve as the control.…”

“…The participants were tasked to rank order the cards, starting with the one that appeared to have the smallest inner circle and ending with the one that appeared to have the largest inner circle. Jaeger and Klahs (2015) reasoned that the size-contrast and biphasic contour interaction theories each predict a different set of results from their experiment. According to size-contrast theory, the inner circle should appear larger as a function of the number of tiny circles added -in a manner similar to how an average-sized person would appear smaller when surrounded by a greater number of professional basketball players over six feet (or 2 metres) tall (Massaro & Anderson, 1971).…”

“…Reading Jaeger and Klahs (2015) led us to consider other ways in which one could test the biphasic contour interaction theory. One simple way would be to examine the effects of a different illusion which can be more parsimoniously explained by the biphasic contour interaction theory and see whether or not variability in susceptibility to this illusion is shared with variability in susceptibly to the Ebbinghaus illusion in the same cohort of participants.…”