Generalization of adaptation to a complex visuo-motor transformation across the workspace.

For the efficient use of tools, the visuo-motor transformation relating body movements to movements of the effective part of the tool has to be learned. Here we ask whether adaptation to a complex tool transformation generalizes to new regions of the workspace of the tool. Three groups of participants performed goal-directed movements of a cursor on a computer monitor. The cursor represented the tip of the load arm of a sliding lever, while the hand of the participants moved the tip of the effort arm of the same lever. Each group learned a particular relation between movements of the effort arm and of the load arm as it was associated with a certain region of the workspace. In the transfer test, targets in three different regions of the workspace were presented, only one of them each group had encountered during practice. Adaptation to the visuo-motor transformation turned out to generalize across the workspace of the tool. However, the generalization exhibited different patterns for the three groups which reflected the respective regions of the workspace where the transformation had been learned. We conclude that the acquired internal representation of the visuo-motor transformation is local and does not allow extrapolation to new regions of the workspace. It likely consists of a symmetry approximation, which is valid across the whole workspace of the tool and largely accessible to conscious awareness, and a rather implicit local fine tuning, which is specific to local regions of the workspace.