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The frog hand illusion: Distortion of hand shape in inverted presentation
Shuichiro Taya1, Achille Pasqualotto2
1Hiyoshi Psychology Laboratory, Keio University, Japan.
I-Perception
|March 3, 2025
Summary
The frog hand illusion (FHI) makes inverted hand photos appear shorter. This study quantified FHI, finding no dominant hand effect, suggesting perceptual constancy attenuation.
Area of Science:
- Psychology
- Neuroscience
- Visual Perception
Background:
- The frog hand illusion (FHI) describes the visual distortion where an inverted image of a hand appears squashed with shortened fingers.
- Understanding FHI may offer insights into visual perception and the brain's processing of body image.
Purpose of the Study:
- To quantitatively measure the magnitude of the frog hand illusion.
- To investigate if hand dominance influences the strength of the frog hand illusion.
Main Methods:
- The study employed the method of constant stimuli to measure the perceived shortening of fingers in inverted versus upright hand images.
- Participants viewed photographs of the back of a hand with fingers extended.
Main Results:
- Fingers in the inverted hand images were perceived as approximately 5% shorter on average compared to upright images.
- No significant difference was found in the strength of the frog hand illusion between dominant and non-dominant hands.
Conclusions:
- The frog hand illusion can be reliably quantified, demonstrating a consistent perceptual distortion.
- The findings suggest that the frog hand illusion is not influenced by hand dominance.
- A proposed hypothesis is that FHI results from reduced perceptual constancy due to viewing the hand from an unusual perspective.
