Bimanual grasping does not adhere to Weber's law

Area of Science:

• Cognitive Psychology
• Neuroscience
• Human Perception

Background:

• Weber's law describes how visual resolution decreases linearly with object size in perception.
• Previous research indicated grasping actions deviate from Weber's law, but was limited by stimulus size range.
• The dissociation between perception and action regarding Weber's law needed further investigation across different motor tasks.

Purpose of the Study:

• To test if the dissociation between perception and action holds for bimanual grasping.
• To examine visual resolution across a wide range of object sizes during bimanual grasping and perception.
• To determine if visuomotor control relies on absolute or relative size representation.

Main Methods:

• Participants performed bimanual grasps and perceptual size estimations of large objects.
• Visual resolution during perception and action was measured across a broad range of stimulus sizes.
• The study compared adherence to Weber's law in grasping versus perceptual tasks.

Main Results:

• Bimanual grasps consistently violated Weber's law across the entire movement.
• Perceptual estimations showed Just Noticeable Differences (JNDs) increasing linearly with object size, adhering to Weber's law.
• A clear dissociation was observed between perceptual and action-based size processing.

Conclusions:

• Visuomotor control for grasping, even with two hands, does not follow Weber's law.
• Perceptual size judgments align with Weber's law, indicating a different processing mechanism.
• Findings suggest visuomotor control relies on absolute object size representation, not relative size, across various actions and sizes.