Contrasting Three Popular Explanations for the Muller-Lyer Illusion

Abstract

Problem statement: Using the method of adjustment, participants compared the line lengths of 'dumbbell' and 'spectacle' versions of Muller-Lyer (circles and ovals at the endpoints in place of arrowheads). Approach: Three popular competing explanations for the illusion (conflicting cues, misapplied size constancy scaling and confusion hypothesis) make differing predictions concerning the pattern of change in illusion strength when the bounding elements are varied. Results: PSEs were computed for circle and spectacle versions of Muller-Lyer, in which the end points were varied in size or orientation. A set of planned comparisons were carried out between the baseline versions of the illusion (with small endpoints) and the other configurations where the inner, outer, or both bounding elements were altered. Increasing the size of the inner bounding circles, as well as the inner and outer bounding spectacles, gave rise to significant increases in the illusion size (although the effect was not additive), however increasing the size of the outer bounding circles resulted in an unexpected significant decrease in illusion size not predicted by any model considered here (all differences significant at p<0.005). It is possible that this unusual result is due to the bounding elements being perceived as separate from the line being bound. Conclusion/Recommendations: In summary, Confusion Hypothesis came closest to predicting the observed pattern of results however a complete explanation requires a combination of Misapplied Size Constancy Scaling, Confusion Hypothesis and the Ebbinghaus illusion.

Perceptual similarity and the neural correlates of geometrical illusions in human brain structure

“…The scene integration process might be particularly evident in the Muller-Lyer, Ebbinghaus and Ponzo illusions, where the surrounding figure elements (e.g., arrows in the Muller-Lyer) influence judgment of the target (e.g., the line length in the Muller-Lyer). In addition, it has also been repeatedly suggested that the illusory phenomenon might arise from an inappropriate interpretation of a 2-D image as a 3-D scene3518. The most explored flavor of this idea has been the misapplied size-constancy scaling theory1617 that proposed potential explanations for Muller-Lyer, Ponzo, and vertical-horizontal illusions.…”

“…That is, today, after many years of research, for the well-known illusions, such as the Ebbinghaus or Muller-Lyer, there are at least half a dozen potential explanations that are backed up by empirical results (for reviews, see refs 3 and 41). Critically, if we assume that only one of these explanations is correct, it is unclear how the current corpus of empirical evidence would be reconciled.…”

“…Numerous proposals explaining the reasons for illusory effects have been advanced, but no clear consensus has been reached2. Empirical research on illusions has been confined mostly to the exploration of each illusion separately, by manipulating their configurations (e.g., changing the shape of arrows in the Muller-Lyer illusion3). In a quest for unifying mechanisms of illusions, prominent theoretical proposals have been made4567.…”

“…15), here we asked whether more high-level, visuospatial mechanisms might also play a role in the misjudgment of geometrical illusions. That is, according to prominent misapplied size-constancy scaling theory1617, the illusory effect for illusions like Muller-Lyer, Ponzo, and vertical-horizontal might be related to erroneously perceiving the lines of different distance, while the visual system implicitly transforms the 2-D image to a 3-D scene318. Furthermore, geometrical illusions like Muller-Lyer, Ebbinghaus, and Ponzo can be conceptualized as complex scenes, consisting of target elements (i.e., elements that are compared) and spatial inducer elements (i.e., elements that influence the illusory percept).…”

Top-down Approach to the Investigation of the Neural Basis of Geometric-optical Illusions: Understanding the Brain as a Theoretical Entity

“…The main question of the present analysis is whether perceptual principles derived from these theories can guide researchers to the discovery of a common neural mechanism for the realization of such perceptual phenomena2 (31)(32)(33)(34)(35). In the following sections, it will be explained how a top-down strategy of research may lead to such a success in studying illusions in human population.…”