Grip force when reaching with target uncertainty provides evidence for motor optimization over averaging

Area of Science:

• Neuroscience
• Motor Control
• Human Movement Science

Background:

• Humans often face situations with multiple potential goals.
• Understanding how the brain plans movements under uncertainty is crucial for explaining adaptive behavior.

Purpose of the Study:

• To investigate whether the brain averages motor plans or selects a single optimal plan when movement targets are uncertain.
• To differentiate between averaging and single-movement planning hypotheses in motor control.

Main Methods:

• Participants performed reaching and grasping tasks with a robotic device applying elastic loads.
• Target uncertainty was manipulated by presenting one or two potential targets.
• Grip force and initial hand trajectory were measured to infer motor planning.

Main Results:

• When presented with two potential targets, participants initially reached towards the average direction.
• Crucially, initial grip force was minimal, matching a midline movement, not an average of forces for individual targets.
• This indicates the motor system planned a single movement, not an average of multiple plans.

Conclusions:

• Under target uncertainty, the brain does not average potential motor plans.
• Instead, it appears to plan and execute a single movement that optimizes for motor costs.
• This finding provides insight into the neural mechanisms of decision-making and action selection in uncertain environments.