Upright Posture: A Singular Condition Stabilizing Sensorimotor Coordination

Area of Science:

• Neuroscience
• Human motor control
• Biomechanics

Background:

• The nervous system's reliance on gravity for sensory alignment is hypothesized.
• Hand-path orientation drift occurs in weightlessness and supine postures but not upright.
• Factors influencing drift magnitude and conditions are not fully understood.

Purpose of the Study:

• Investigate if upright posture, a biomechanical singularity due to gravity, prevents hand-path orientation drift.
• Determine the precise conditions and influencing factors for sensory drift.

Main Methods:

• Human participants performed point-to-point arm movements with eyes open and closed.
• Movements were executed in various body orientations: upright, and tilted backward (45°, 90°, 135°).
• Hand-path orientation drift was measured in each condition.

Main Results:

• Drift in hand-path orientation was observed in the eyes-closed condition only when the body was tilted.
• No drift was detected in the upright, eyes-closed condition.
• Drift magnitude and direction were consistent across all tested tilted orientations.

Conclusions:

• Upright posture uniquely facilitates sensorimotor transformations.
• The upright posture prevents drift in hand-path orientation when visual input is absent.
• Gravity's role in sensorimotor control is critical, especially in maintaining orientation without visual cues.