[Errors in pointing under various body orientation relative to the gravity vector]

Area of Science:

• Neuroscience
• Motor Control
• Human Physiology

Background:

• Human motor control involves complex interactions with the sensory environment.
• The orientation of the body relative to the gravity vector is a significant factor in sensorimotor adaptation.

Purpose of the Study:

• To investigate the impact of body position (upright, supine, prone) on pointing accuracy to remembered targets.
• To determine how changes in orientation relative to gravity affect specific types of pointing errors.

Main Methods:

• Healthy subjects performed pointing tasks to remembered locations in three different body orientations.
• Analysis focused on systematic (X and Y) and variable errors in pointing accuracy.

Main Results:

• Horizontal (X) pointing error remained consistent across body positions.
• Vertical (Y) pointing error showed a significant dependence on body orientation relative to gravity.
• Variable error in pointing was modulated by the orientation of the movement trajectory relative to gravity, being larger in the supine and smaller in the prone position compared to upright.

Conclusions:

• Gravity introduces a bias in pointing errors, suggesting that motor programs are not fully recalibrated for altered gravitational orientations when lying down.
• These findings highlight the continuous influence of gravity on motor planning and execution, even when not explicitly adapted for.