The Mystery Spot Illusion and its Relation to Other Visual Illusions

Observations at The Mystery Spot, a roadside attraction near Santa Cruz, California, suggest intriguing visual illusions based on tilt-induced effects. Specifically, a tilted spatial background at The Mystery Spot induced misperceptions of the orientation of the cardinal axes (i.e., true horizontal and vertical), which then led to illusions in the perceived height of twoindividuals. This illusion was assessed at The Mystery Spot and replicated in the laboratory using pictorial and lined displays rotated in the picture plane. These findings are described in terms of the orientation framing theory, which suggests that these and other tilt-induced illusions (e.g., Ponzo illusion, Zöllner illusion) can be attributed to distorted frames of reference.