Deciding when and how to correct a movement: discrete submovements as a decision making process

Area of Science:

• Neuroscience
• Motor Control
• Primate Behavior

Background:

• Rapid reaching movements in primates often display irregular velocity profiles.
• The interpretation of these irregularities is debated, with theories suggesting continuous control versus discrete corrective actions.

Purpose of the Study:

• To investigate the nature of movement corrections during rapid wrist movements in monkeys.
• To determine the influence of visual perturbations on movement control and corrective submovements.

Main Methods:

• Analysis of rapid pronation/supination wrist movements in monkeys during a 1D step-tracking task.
• Application of an algorithm to decompose movements into primary and corrective submovements.
• Introduction of random visual perturbations at movement onset.

Main Results:

• Visual perturbations minimally affected primary movements but significantly influenced the type and extent of corrective submovements.
• The timing of corrective submovements depended on movement error estimates and remaining movement extent, not directly on visual perturbations.
• Results support an intermittent controller model where corrections are initiated based on statistically significant predicted errors.

Conclusions:

• Rapid movements are controlled by an intermittent system generating discrete corrections rather than continuous interaction with the environment.
• The controller utilizes a forward model incorporating error prediction and variance to determine the necessity and characteristics of corrective submovements.
• This model accurately accounts for observed movement corrections and their timing in primate wrist movements.