Concavities, negative parts, and the perception that shapes are complete

Area of Science:

• Cognitive Science
• Computer Vision
• Psychology

Background:

• Object shape perception allows for inferences beyond local geometry.
• Concavities in shapes can result from various causes, not solely excision (e.g., spaces between fingers).
• Identifying excision requires specific geometrical conditions beyond mere concavity detection.

Purpose of the Study:

• To investigate the geometrical conditions for perceiving shapes as bitten versus whole.
• To understand how humans infer excision from object shapes.
• To explore the relationship between shape features and the perception of damage.

Main Methods:

• Created 2-D shapes by intersecting irregular hexagons and removing overlap regions.
• Subjects rated shapes on a 10-point scale for perceived "bittenness" or wholeness.
• Analyzed geometrical features to determine their predictive power for human judgments.

Main Results:

• Subjects could reliably distinguish between bitten and whole shapes above chance levels.
• Judgments of bitten shapes showed high consistency across subjects.
• The relative depth of the negative part (concavity) was a strong predictor of perceived "bittenness".

Conclusions:

• Perception of excision is guided by specific geometrical cues, particularly the depth of concavities.
• Shape perception involves inferring causal events like excision, not just processing local features.
• Findings contribute to understanding perceptual organization and attribute inference from object shapes.