title: Controlling reaching movements during self-motion: body-fixed versus Earth-fixed targets.
abstract: The control of goal-directed arm movements performed during whole-body displacements is far from being understood. Recent studies suggested that the compensatory arm movements that allow individuals to preserve hand-in-space trajectory during unexpected body motion are controlled by sensorimotor, automatic- like processes. We tested this hypothesis comparing both the accuracy of movements directed towards body-fixed or Earth-fixed target during body rotations and the amount of interference of the reaching tasks on a concurrent cognitive task. Participants reached for a memorized 55 cm distant straight-ahead target in darkness which was about 20 cm lower than the initial finger position. The target was either body-fixed or Earth-fixed. At reaching onset, participants could be rotated in yaw. The concurrent task consisted of a verbal reaction time (RT) to an auditory stimulus. RTs increased when participants reached for the target while they were rotated. However, this increase was not significantly different for body-fixed and Earth-fixed targets. Reaching accuracy was greater for body-fixed than for Earth-fixed targets. A control experiment suggested that the errors in the Earth-fixed target condition arose from a difficulty in the organization of movements which necessitate both the production of active forces at the shoulder joint (to compensate for body rotation) and a concomitant decrease of muscular activation to lower the arm during reaching movements. These findings suggest that reaching for Earth-fixed or body-fixed targets during body rotation cannot be considered as being purely automatic tasks.
authors.affiliation: UMR Mouvement & Perception, CNRS et Universite de la Mediterranee, Marseille, France.
authors.forename: Etienne
authors.initials: E
authors.lastname: Guillaud
authors.forename: Martin
authors.initials: M
authors.lastname: Simoneau
authors.forename: Gabriel
authors.initials: G
authors.lastname: Gauthier
authors.forename: Jean
authors.initials: J
authors.lastname: Blouin
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D001132:Arm / Q000502:physiology*; D001696:Biomechanical Phenomena; D005385:Fingers / Q000502:physiology*; D006801:Humans; D008568:Memory; D009043:Motor Activity / Q000502:physiology*; D011434:Proprioception / Q000502:physiology*; D011930:Reaction Time; D012399:Rotation; D013647:Task Performance and Analysis