Simultaneous adaptation and switching for two viscous force fields

In this study, two different viscous force fields are generated by using a PFM (parallel link direct-drive air-magnet floating manipulandum), and the responding human learning process for multi-joint reaching motion is observed. In this experiment, the subject is given a certain cue for the force field. The cues are provided as follows: (1) audiovisual cue (a color and a peep sound corresponding to the force field, and a feather pattern representing the direction and magnitude of the force) and (2) movement cue (two trials are defined as a set, and the first movement is used as the cue). The task of the experiment is to learn the movement in force fields which are switched at random. Whichever cue (1) or (2) is used, there is a tendency that the area error from the desired straight trajectory decreases with an increasing number of trials. It is also observed that when the force field is eliminated at random after learning, a marked aftereffect arises in the group to which the audiovisual cue is given. The aftereffect is also observed in the group to which the movement cue is given, but is not as marked as in the group to which the audiovisual cue is given. The above results suggest that the internal models for two different viscous force fields can be acquired simultaneously without time separation by providing an appropriate cue to indicate the force field and learning in the environment in which the force field is switched at random.