Perception-action dissociation generalizes to the size-inertia illusion

Area of Science:

• * Cognitive Psychology
• * Human Motor Control
• * Perception Science

Background:

• * The size-weight illusion demonstrates a discrepancy between perceived heaviness and actual mass, with larger objects feeling lighter.
• * Previous research suggests a dissociation between perceptual judgments and motor responses, as grip forces adapt to true weight while the illusion persists.

Purpose of the Study:

• * To investigate if the size-weight illusion is maintained when mass is perceived through inertial cues instead of gravitational cues.
• * To examine the influence of uncorrelated mass and size stimuli on the size-weight illusion and motor control.
• * To analyze anticipatory grip force adjustments in response to both visual size and haptic mass.

Main Methods:

• * 10 participants manipulated 33 objects with uncorrelated masses and sizes in both gravitational and inertial conditions.
• * Objects were presented on a frictionless air-bearing slide, oriented vertically or horizontally.
• * Grip force was measured before motion onset to assess anticipatory motor behavior.

Main Results:

• * The size-weight illusion effect was quantitatively similar across gravitational and inertial conditions.
• * Anticipatory grip control showed negligible influence from visual size and haptic mass.
• * Motor responses adapted to true object weight, irrespective of the sensory cues (gravitational vs. inertial).

Conclusions:

• * The size-weight illusion is robust and occurs regardless of whether mass is perceived via gravity or inertia.
• * Anticipatory motor control appears largely independent of visual size and haptic mass cues when dealing with uncorrelated stimuli.
• * The findings reinforce the concept of a dissociation between perceptual and action systems in humans.