A mass-density model can account for the size-weight illusion

Area of Science:

• Cognitive Psychology
• Perception Science
• Human Factors

Background:

• The size-weight illusion, where smaller, denser objects are perceived as heavier than larger objects of equal mass, remains incompletely explained by existing theories.
• Current models struggle to account for all facets of human heaviness perception and the size-weight illusion.

Purpose of the Study:

• To propose and validate a novel maximum-likelihood estimation model for heaviness perception.
• To investigate how the reliability of density information influences the size-weight illusion.

Main Methods:

• Developed a maximum-likelihood estimation model integrating mass and density estimates with correlated noise.
• Conducted magnitude estimation and two-alternative forced choice experiments involving lifting objects of varying mass, density, and volume information quality.
• Manipulated the reliability of visual and haptic volume information to assess its impact on heaviness judgments.

Main Results:

• Heaviness judgments were increasingly biased by object density as the quality of volume information improved.
• Objects of identical density were perceived as more similar in heaviness.
• Larger objects were perceived as lighter than smaller, denser objects of equal mass, with this effect strengthening with increased density differences.

Conclusions:

• The proposed model successfully explains the size-weight illusion as a density-biased perception, rather than size-biased.
• The findings suggest that perceived heaviness is a weighted average of mass and density estimates, with weights determined by their relative reliability.
• The model offers a promising framework for unifying theories of the size-weight illusion and human heaviness perception.