The moon size illusion does not improve perceptual judgments.

Area of Science:

• Visual perception
• Cognitive psychology
• Neuroscience

Background:

• Perceptual judgments can be influenced by illusory size, with greater accuracy for larger perceived sizes.
• Neuroscientific evidence suggests early visual areas represent perceived (illusory) size over physical size.
• The moon illusion, where the moon appears larger near the horizon, provides a naturalistic test case.

Purpose of the Study:

• To investigate the relationship between the moon illusion's magnitude and perceptual judgment accuracy.
• To test if enhanced illusory size correlates with improved accuracy, as suggested by prior research.

Main Methods:

• 230 participants viewed a smartphone image of the moon.
• Participants adjusted the image's orientation to match the perceived orientation of the moon in the sky.
• Perceptual judgment accuracy was measured based on orientation matching performance.

Main Results:

• Contrary to previous findings, perceptual judgment accuracy was slightly lower when the moon appeared larger (near the horizon).
• Accuracy was higher when the moon appeared smaller (higher in the sky).

Conclusions:

• The study's findings challenge the notion that increased illusory size consistently enhances perceptual judgment accuracy.
• The moon illusion's effect on accuracy may be more complex than previously assumed, potentially differing from other size illusions.