The apparent distance of interior and exterior corners: a test of Gregory's misapplied size constancy explanation for the Mueller-Lyer illusion.

Key to Gregory's misapplied size constancy explanation for the Mueller-Lyer illusion is the assumption that subjects perceive the central line segment of the fins-out figure, which is analogous to an interior corner, as projecting from a more distant object than does the central line segment of the fins-in figure, which is analogous to an exterior corner. We examined the validity of this assumption by having 20 college students judge the relative distance of three-dimensional model corners, presented in a monocular viewing box. The interior corner was perceived to be nearer than the exterior corner, indicating that the key assumption in Gregory's theory is either false or unfalsifiable.