Sustained Facilitation of Embodied Fake Hand Movement on Voluntary Movement Execution.

Area of Science:

• Neuroscience
• Cognitive Psychology
• Somatosensory Research

Background:

• The rubber hand illusion (RHI) induces illusory ownership of a fake hand.
• Previous studies show faster reaction times (RTs) in RHI participants observing fake hand movements.
• The source of this RT facilitation remains debated: visual processing or motor facilitation.

Purpose of the Study:

• To investigate whether RT facilitation in RHI is due to enhanced visual processing or motor facilitation from visuo-proprioceptive conflict.
• To differentiate between visual and motor contributions to RHI-related RT benefits.

Main Methods:

• Two experiments were conducted using the RHI paradigm.
• Participants lifted their index finger upon an auditory cue after observing fake finger movements.
• Stimulus onset asynchrony (SOA) between visual and auditory stimuli was varied (500, 1000, 1500 ms).
• Experiment 1: Fake finger remained elevated until participant movement; Experiment 2: Fake finger lowered shortly after visual stimulus.

Main Results:

• The RT advantage in the RHI condition was independent of SOA.
• This RT benefit was observed exclusively in Experiment 1, where the fake finger remained elevated.
• No significant differences in peak velocity or acceleration of finger movement were found between conditions.

Conclusions:

• The ownership-dependent RT facilitation in RHI is not solely due to enhanced visual processing.
• Motor facilitation mechanisms, driven by visuo-proprioceptive discrepancy at movement termination, likely underlie the observed RT benefits.
• The RHI influences motor responses through a conflict between perceived and actual limb position.