Controlling reaching movements during self-motion: body-fixed versus Earth-fixed targets

Motor Control. 2006 Oct;10(4):330-47. doi: 10.1123/mcj.10.4.330.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acoustic Stimulation
  • Adult
  • Arm / physiology*
  • Biomechanical Phenomena
  • Fingers / physiology*
  • Humans
  • Memory
  • Motor Activity / physiology*
  • Proprioception / physiology*
  • Reaction Time
  • Rotation*
  • Task Performance and Analysis