Touching curvature and feeling size: a contrast illusion

Area of Science:

• Psychology
• Neuroscience
• Haptics

Background:

• The sense of touch (haptics) is crucial for object interaction.
• Previous research indicates accurate size perception via pinch grip.
• The influence of local surface geometry on haptic size perception is less understood.

Purpose of the Study:

• To investigate the effect of local surface curvature on haptic size perception.
• To determine if curvature can lead to systematic errors in size estimation.
• To propose a mechanism for curvature-induced haptic size illusions.

Main Methods:

• Participants performed a pinch grip on objects with varying sizes and local curvatures.
• Haptic size perception was assessed through subjective reports and comparative judgments.
• Statistical analyses were used to correlate curvature with size misperceptions.

Main Results:

• Local surface curvature significantly influenced perceived object size.
• Concave and convex curvatures led to systematic under- and overestimations, respectively.
• These illusions occurred even when actual object size remained constant.

Conclusions:

• Haptic size perception is susceptible to illusions induced by local surface curvature.
• A contrast mechanism between finger separation and inferred curvature-size relationships may explain these findings.
• This study reveals a novel factor influencing tactile size judgments in a pinch grip.