Real and subjective contour Poggendorff illusions: no differences based on eye color

Area of Science:

• Visual perception
• Psychophysics
• Optical illusions

Background:

• The Poggendorff illusion is a well-documented visual illusion.
• Previous research suggested a link between iris pigmentation and illusion magnitude.
• The role of subjective contours in visual illusions requires further investigation.

Purpose of the Study:

• To investigate the effect of eye color on the magnitude of the Poggendorff illusion.
• To determine if subjective contours influence the relationship between eye color and illusion perception.
• To test the hypothesis that intersecting lines are the basis of the iris-pigmentation effect.

Main Methods:

• Participants: Large sample of undergraduate students with dark and light eyes.
• Stimuli: Real contour and two subjective contour Poggendorff figures.
• Procedure: Measured illusion magnitude for each figure type across participants.

Main Results:

• Illusion magnitude differed significantly based on the type of Poggendorff figure presented.
• Eye color (dark vs. light) did not produce a significant overall effect on illusion magnitude.
• No significant interaction was found between eye color and figure type.

Conclusions:

• The findings do not support a link between iris pigmentation and Poggendorff illusion magnitude.
• Subjective contour Poggendorff figures do not modulate the effect of eye color.
• The basis of previously reported iris-pigmentation effects in visual illusions may not be related to intersecting lines.