title: Adaptation to a novel multi-force environment.
abstract: Humans display accurate limb behavior when they move in familiar environments composed of many simultaneously-acting forces. Little is known about how multi-force environments are represented and whether this process partitions between the underlying force components, reflects the net forces present, or is cued to the force-context. We tested between these three main alternatives by examining how reaching movements adapt to a novel multi-force field composed of a velocity-dependent force and a constant force. These hypotheses were dissociated first by making the constant force larger and oppositely-oriented to the velocity-dependent force; thereby, the net force was always opposite the velocity-dependent component. Second, we tested adaptation with all novel forces removed to eliminate any potential cues for the force-context. In two experiments that used forces perpendicular or parallel to the forward movement direction, we found adaptation aftereffects consistent with a mechanism that partitioned the velocity-dependent component from the net force field. Specifically, we found aftereffects opposite the rightward or resistive velocity-dependent component of the multi-force field, even though the net force imposed was leftward or assistive, respectively. An additional experiment suggested that the velocity-dependent component is partitioned relative to the background load in a limb-based coordinate frame.
authors.affiliation: Ashton Graybiel Spatial Orientation Laboratory, Volen Center for Complex Systems, Brandeis University, 415 South St. Waltham, MA, 02454, USA. isaac@biomed.queensu.ca
authors.forename: Isaac
authors.initials: I
authors.lastname: Kurtzer
authors.forename: Paul A
authors.initials: PA
authors.lastname: DiZio
authors.forename: James R
authors.initials: JR
authors.lastname: Lackner
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000293:Adolescent; D000328:Adult; D001132:Arm / Q000502:physiology*; D001696:Biomechanical Phenomena; D002490:Central Nervous System / Q000502:physiology; D005260:Female; D006112:Gravitation; D006801:Humans; D008297:Male; D008959:Models, Neurological; D009068:Movement / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology; D016474:Weight-Bearing / Q000502:physiology