The hidden hand is perceived closer to midline

Area of Science:

• Neuroscience
• Cognitive Psychology
• Human Perception

Background:

• Proprioception, the sense of self-movement and body position, is crucial for interacting with the environment.
• Accurate perception of hand location is fundamental for self-awareness and motor control, even without visual input.

Purpose of the Study:

• To investigate the accuracy of perceived hand location in the absence of vision.
• To determine how hand distance from the body midline and the presence of the contralateral hand affect perceived location.

Main Methods:

• Thirty participants had their right index finger placed at varying distances (10, 20, 30 cm) from the body midline, with and without the left index finger present.
• Perceived hand location was assessed without visual feedback.
• Statistical analysis was performed to quantify underestimation and the effects of hand position and contralateral limb presence.

Main Results:

• Participants systematically underestimated the distance of their right hand from the body midline.
• This underestimation increased linearly as the hand moved further from the midline (slope 0.77).
• Perceptual errors were smaller when the right hand was in the contralateral workspace; the presence of the left hand had minimal effect.

Conclusions:

• Systematic perceptual errors in hand location occur immediately after placement, especially without vision.
• The magnitude of these errors escalates with greater distance from the body midline, potentially affecting motor planning.
• Findings are relevant for understanding body ownership illusions and proprioceptive drift.