Relative spatial expansion and contraction within the Müller-Lyer and Judd illusions

Area of Science:

• Visual perception
• Psychophysics
• Cognitive psychology

Background:

• The Müller-Lyer illusion is a well-known visual illusion affecting perceived line length.
• Previous research suggested size-constancy mechanisms might explain the M-L illusion.
• The distribution of perceived length distortion along the figure's shaft remained unclear.

Purpose of the Study:

• To investigate the spatial distribution of perceived length distortion in various geometric figures.
• To test the hypothesis that the M-L illusion results from uniform size scaling.
• To compare distortion patterns across Müller-Lyer, one-ended M-L, and Judd figures.

Main Methods:

• Subjects bisected the shaft portions of Müller-Lyer, one-ended M-L, Judd figures, and their controls into eight equal intervals.
• Perceived length of segments was analyzed relative to actual length.
• Localization responses were also assessed.

Main Results:

• Perceived length distortion in the M-L illusion is not uniform along the shaft.
• Control stimuli showed overestimation of the left shaft half.
• One-ended M-L figures exhibited distortion extending further along the shaft than standard M-L figures.
• Judd figures showed systematic variation in perceived length from underestimation to overestimation.

Conclusions:

• The findings contradict the size-constancy hypothesis predicting uniform distortion.
• Perceptual distortion in these illusions is spatially non-uniform.
• The results offer new insights into the mechanisms underlying visual length perception and illusions.