The Propriocpetive Aftereffects of Prism Adaptation Influence Interlimb Rhythmic Coordination

Adaptation to prisms can produce a change in felt arm position, termed proprioceptive shift. We studied the effects of prism-induced proprioceptive shift on interlimb rhythmic coordination performed under haptic (proprioceptive) guidance, in the absence of vision. Relative to interlimb rhythmic coordination performed before prism exposure, the observed steady states of relative phase for post-exposure coordination were shifted by a small but reliable amount. The shift was in the direction expected given the direction of optical displacement. The amount of variability of interlimb rhythmic coordination was unaffected by prism exposure. The implications of the results apply to virtual environment design.

Speculations on a Model of Prism Adaptation

Arguments and evidence are presented that prism adaptation results in a third end state in addition to the ‘traditional’ components of ‘proprioceptive shift’ and ‘visual shift’. That is, under certain conditions (most importantly, ones involving error-corrective feedback), exposure to prism-displaced vision induces a motor-learning component, referred to here as an ‘assimilated corrective response’. Thus the postexposure error in target pointing, the ‘negative aftereffect’, is postulated to be the algebraic sum of proprioceptive shift, visual shift, and an assimilated corrective response—at least in certain situations. Support for the existence of this third component as a form of learning is seen in the fact that it occurs primarily when prism exposure involves target-pointing experience, and that it is apparently subject to the effects of some ‘learning variables’.