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Optical origins of opposing facial expression actions
Daniel H Lee1, Reza Mirza, John G Flanagan
11Department of Psychology, University of Toronto.
Psychological Science
|January 28, 2014
Summary
Emotional expressions like fear and disgust may have evolved from an optical trade-off in eye function. Widening eyes boosts detection, while narrowing eyes improves discrimination, impacting early visual encoding.
Area of Science:
- Evolutionary biology
- Vision science
- Psychology
Background:
- Charles Darwin proposed emotional expressions are functional adaptations for the expresser.
- The cornea provides two-thirds of the eye's refractive power.
- Opposing facial expressions alter eye aperture.
Purpose of the Study:
- To investigate if opposing eye expressions (widening vs. narrowing) represent an optical trade-off.
- To determine if these expressions enhance visual sensitivity or acuity.
- To link these visual changes to stimulus localization ('where') and discrimination ('what').
Main Methods:
- Developed an optical model of eye apertures for fear and disgust expressions.
- Utilized standardized optometric measures for visual sensitivity and acuity.
- Empirically tested the model's predictions.
Main Results:
- Eye widening significantly enhanced stimulus detection (sensitivity).
- Eye narrowing significantly enhanced stimulus discrimination (acuity).
- Each function occurred at the expense of the other, confirming an optical trade-off.
Conclusions:
- Opposing eye expressions may originate from an optical principle, not solely social signaling.
- These expressions shape visual encoding by altering how light is cast on the retina.
- This provides a functional, optical explanation for the evolution of certain emotional expressions.
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