Three-dimensional curvature contrast--geometric or brightness illusion?

Area of Science:

• Visual perception
• Computational neuroscience
• Psychophysics

Background:

• Simultaneous contrast effects are well-documented across various visual dimensions.
• Previous research has not fully explored contrast effects related to three-dimensional (3D) surface curvature.

Purpose of the Study:

• To describe and investigate a novel simultaneous contrast effect: 3D curvature contrast.
• To determine if 3D curvature contrast relies on internal curvature representation or local luminance changes.
• To explore the role of global versus local processing in shape perception.

Main Methods:

• Experimental manipulation of surface curvature using shading and texture information.
• Presentation of test patches surrounded by inducing curved surfaces.
• Photographic negative transformation of inducing patterns to isolate luminance vs. structure effects.
• Varying spatial separation between inducing and test surfaces.

Main Results:

• A strong and measurable 3D curvature contrast effect was observed, where apparent surface curvature is influenced by surrounding curvature.
• Luminance contrast contributes to perceived curvature changes, but does not fully explain the effect.
• Disrupting 3D structure via photographic negatives significantly weakened the illusion, indicating a role for curvature representation.
• The effect persisted even with spatially separated inducing surfaces.

Conclusions:

• 3D curvature contrast is a distinct perceptual phenomenon.
• Perceived curvature involves comparisons at the level of surface curvature representation, not solely luminance contrast.
• Shape perception utilizes both global and local visual processing operations.