Our capacity to learn multiple dynamic and visuomotor tasks is limited by the time between the presentations of the tasks. When subjects are required to adapt to equal and opposite position-dependent visuomotor rotations (Krakauer et al., 1999) or velocity-dependent force fields (Brashers-Krug et al., 1996) in quick succession, interference occurs that prevents the first task from being consolidated in memory. In contrast, such interference is not observed between learning a positiondependent visuomotor rotation and an acceleration-dependent force field. On the basis of this finding, it has been argued that internal models of kinematic and dynamic sensorimotor transformations are learned independently (Krakauer et al., 1999). However, these findings are also consistent with the perturbations interfering only if they depend on the same kinematic variable. We evaluated this hypothesis using kinematic and dynamic transformations matched in terms of the kinematic variable on which they depend. Subjects adapted to a positiondependent visuomotor rotation followed 5 min later by a position-dependent rotary force field either with or without visual feedback of arm position. The force field tended to rotate the hand in the direction opposite to the visuomotor rotation. To assess learning, all subjects were retested 24 hr later on the visuomotor rotation, and their performance was compared with a control group exposed only to the visuomotor rotation on both days. Adapting to the position-dependent force field, both with and without visual feedback, impaired learning of the visuomotor rotation. Thus, interference between our kinematic and dynamic transformations was observed, suggesting that the key determinant of interference is the kinematic variable on which the transformation depends. Key words: motor learning; internal models; arm movement; visuomotor rotation; force field; motor memoryThe problem of motor learning is one of mastering novel sensorimotor transformations that relate motor commands to sensory outcomes. Such learning involves the acquisition of internal models that capture these sensorimotor transformations and enable the CNS to accurately estimate the motor commands required to achieve desired outcomes and to predict the consequences of actions (Johansson and Cole, 1992;Miall et al., 1993;Shadmehr and Mussa-Ivaldi, 1994;Wolpert et al., 1995;Conditt et al., 1997;Flanagan and Wing, 1997;Kawato, 1999;Wolpert and Ghahramani, 2000). Two classes of sensorimotor transformations have been widely used in motor control research: kinematic and dynamic. Kinematic transformations are mappings between different geometric variables (and their derivatives) and, importantly, do not depend on the dynamic properties of the system. In contrast, dynamic transformations relate motor commands to the motion of the system; therefore, they do depend on dynamic properties such as inertia and viscosity. Thus, for example, to control a computer mouse, we must learn the kinematic transformation that relates mouse motion to cursor mot...

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Numerous studies have shown that when people encounter a sudden and novel sensorimotor transformation that alters perceived or actual movement, they gradually adapt and can later recall what they have learned if they encounter the transformation again. In this study, we tested whether retention and recall of learning is also observed when kinematic and dynamic transformations are introduced incrementally such that participants never experience large movement errors. Participants adapted their reaching movements to either a visuomotor rotation of hand position (kinematic transformation) or a rotary viscous force-field applied to the hand (dynamic transformation). These perturbations were introduced either incrementally or instantaneously. Thus, four groups of participants were tested with an incremental and an instantaneous group for both the kinematic and dynamic perturbations. To evaluate retention of learning, participants from all four groups were tested a day later on the same kinematic or dynamic perturbation presented instantaneously (at full strength). As expected, we found that subjects in the instantaneous group retained learning across days. We also found that, for both kinematic and dynamic perturbations, retention was equally good or better when the transformation was introduced incrementally. Because large and clearly detectable movement errors were not observed during adaptation to incremental perturbations, we conclude that such errors are not required for the learning and retention of internal models of kinematic and dynamic sensorimotor transformations.

The results suggest that the values clarification exercises led to better preparation for decision making and to less regret. The impact, however, only emerged after the decision was made.