Unintentional Force Drifts as Consequences of Indirect Force Control with Spatial Referent Coordinates

• Published in: Neuroscience Vol. 481; pp. 156 - 165
• Main Authors: Abolins, Valters, Latash, Mark L.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 15.01.2022
• Subjects: Feedback, Sensory - physiology; finger; Fingers - physiology; force matching; hand; Hand Strength; Humans; kinesthetic perception; Muscles; Psychomotor Performance - physiology; referent coordinate; unintentional drift; finger; RC; referent coordinate; kinesthetic perception; unintentional drift; force matching; CNS; MVC; UCM; hand
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/j.neuroscience.2021.11.006

•Unintentional force drifts are smaller when a person produces force against a spring.•The drift magnitude is smaller when acting against more compliant springs.•Subjects are unaware of the force drift and ignore it when asked to match force.•The results strongly suggest drifts in referent coordinates as causes of force drifts. We explored the phenomenon of unintentional force drifts in the absence of visual feedback. Based on the idea of direct force control with internal models and on the idea of indirect force control with referent coordinates to the involved muscle groups, contrasting predictions were drawn for changes in the drift magnitude when acting against external spring loads. Fifteen young subjects performed typical accurate force production tasks by pressing with the Index finger at 20% of maximal voluntary contraction (MVC) in isometric conditions and while acting against one of the three external springs with different stiffness. The visual feedback on the force was turned off after 5 s. At the end of each 20-s trial, the subjects relaxed and then tried to reproduce the final force level. The force drifts were significantly smaller in the spring conditions, particularly when acting against more compliant springs. The subjects were unaware of the force drifts and, during force matching, produced forces close to the initial force magnitude, which were not different across the conditions. There was a trend toward larger drifts during performance by the dominant hand. We view these observations as strong arguments in favor of the theory of control with spatial referent coordinates. In particular, force drifts were likely consequences of drifts of referent coordinates to both agonist and antagonist muscles. The lack of drift effects on both perception-to-report and perception-to-act fit the scheme of kinesthetic perception based on the interaction of efferent (referent coordinate) and afferent processes.