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Reaching During Virtual Rotation: Context Specific Compensations for Expected Coriolis Forces
Ist Teil von
Journal of neurophysiology, 2000-06, Vol.83 (6), p.3230-3240
Ort / Verlag
Legacy CDMS: Am Phys Soc
Erscheinungsjahr
2000
Quelle
MEDLINE
Beschreibungen/Notizen
Ashton Graybiel Spatial Orientation Laboratory and Volen Center for
Complex Systems, Brandeis University, Waltham, Massachusetts 02454-9110
Cohn, Joseph V.,
Paul DiZio, and
James R. Lackner.
Reaching During Virtual Rotation: Context Specific Compensations
for Expected Coriolis Forces. J. Neurophysiol. 83: 3230-3240, 2000. Subjects who are in an enclosed
chamber rotating at constant velocity feel physically stationary but
make errors when pointing to targets. Reaching paths and endpoints are
deviated in the direction of the transient inertial Coriolis forces
generated by their arm movements. By contrast, reaching movements made
during natural, voluntary torso rotation seem to be accurate, and
subjects are unaware of the Coriolis forces generated by their
movements. This pattern suggests that the motor plan for reaching
movements uses a representation of body motion to prepare compensations
for impending self-generated accelerative loads on the arm. If so,
stationary subjects who are experiencing illusory self-rotation should
make reaching errors when pointing to a target. These errors should be
in the direction opposite the Coriolis accelerations their arm
movements would generate if they were actually rotating. To determine
whether such compensations exist, we had subjects in four experiments
make visually open-loop reaches to targets while they were experiencing
compelling illusory self-rotation and displacement induced by rotation
of a complex, natural visual scene. The paths and endpoints of their
initial reaching movements were significantly displaced leftward during
counterclockwise illusory rotary displacement and rightward during
clockwise illusory self-displacement. Subjects reached in a curvilinear
path to the wrong place. These reaching errors were opposite in
direction to the Coriolis forces that would have been generated by
their arm movements during actual torso rotation. The magnitude of path
curvature and endpoint errors increased as the speed of illusory
self-rotation increased. In successive reaches, movement paths became
straighter and endpoints more accurate despite the absence of visual
error feedback or tactile feedback about target location. When subjects
were again presented a stationary scene, their initial reaches were
indistinguishable from pre-exposure baseline, indicating a total
absence of aftereffects. These experiments demonstrate that the nervous
system automatically compensates in a context-specific fashion for the
Coriolis forces associated with reaching movements.