Reaching around obstacles accounts for uncertainty in coordinate transformations.

Area of Science:

• Neuroscience
• Motor Control
• Human Movement Science

Background:

• Reaching to visual targets requires transforming spatial information into the arm's coordinate system.
• Increased uncertainty in this coordinate transformation, such as during head roll, elevates movement variability and affects decisions.
• It remains unclear if the brain accounts for this added variability in movement planning and execution.

Purpose of the Study:

• To investigate whether the brain incorporates increased movement variability from head roll into reaching and obstacle avoidance strategies.
• To determine if compensatory mechanisms are employed during reaching tasks with altered coordinate transformations.

Main Methods:

• Participants performed an obstacle avoidance reaching task under varying head roll conditions (straight, 30° clockwise, 30° counterclockwise).
• Reaching variability and obstacle avoidance behavior (e.g., movement direction, curvature) were analyzed with and without visual feedback of the hand.
• Coordinate transformation uncertainty was manipulated by head tilt.

Main Results:

• Head roll significantly increased reaching movement variability, consistent with prior research.
• While head roll did not affect collision rates, it systematically altered obstacle avoidance behavior.
• Participants demonstrated adjusted preferred directions for passing obstacles and increased trajectory curvature, indicating enhanced safety margins.

Conclusions:

• The brain actively considers and compensates for increased movement variability arising from coordinate transformations during head roll.
• Compensatory strategies, such as modifying reaching trajectories, are employed to maintain accurate goal-directed movements.
• These findings provide evidence for the brain's adaptive capacity in motor control under conditions of altered body geometry and sensory uncertainty.