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Robotic guidance is an engineered form of haptic-guidance training and intended to enhance motor learning in rehabilitation, surgery, and sports. However, its benefits (and pitfalls) are still debated. Here, we investigate the effects of different presentation modes on the reproduction of a spatiotemporal movement pattern. In three different groups of participants, the movement was demonstrated in three different modalities, namely visual, haptic, and visuo-haptic. After demonstration, participants had to reproduce the movement in two alternating recall conditions: haptic and visuo-haptic. Performance of the three groups during recall was compared with regard to spatial and dynamic movement characteristics. After haptic presentation, participants showed superior dynamic accuracy, whereas after visual presentation, participants performed better with regard to spatial accuracy. Added visual feedback during recall always led to enhanced performance, independent of the movement characteristic and the presentation modality. These findings substantiate the different benefits of different presentation modes for different movement characteristics. In particular, robotic guidance is beneficial for the learning of dynamic, but not of spatial movement characteristics.

Robotic guidance as a means to facilitate motor learning and rehabilitation has received considerable attention during the last few years. However, mixed outcomes suggest that the benefits might be restricted to certain movement characteristics. The authors investigate the effects of robotic guidance on different kinds of motor timing. Two groups of participants performed 2 variants of a circle drawing task in a synchronization-continuation paradigm. One variant was continuous circle drawing (emergent timing), the other variant was intermittent circle drawing (event-based timing). The total duration of movement cycles (absolute timing) and the relative duration of submovements (relative timing) were measured. Half of the participants in each group were guided by a robot device during synchronization (robot-guided group), the other half of the participants received no guidance (control group). Guided participants had superior performance during the synchronization phase with both timing tasks. During continuation there were no benefits of haptic guidance anymore with the continuous circle drawing task. In contrast, with the intermittent circle drawing task guided participants were more accurate in their relative timing than control participants already in the first few trials, and this advantage did not increase in the course of practice. The benefit is thus rather immediate and not cumulative. This finding is consistent with the notion that movement characteristics such as relative timing, which are hard to demonstrate visually or verbally, profit from robotic guidance because of the more accurate demonstrations of the correct movements.

Haptic guidance has been shown to have both facilitatory and interfering effects on motor learning. Interfering effects have been hypothesized to result from the particular dynamic environment, which supports a passive role of the learner, and they should be attenuated by fading guidance. Facilitatory effects, in particular for dynamic movement characteristics, have been hypothesized to result from the high-quality information provided by haptic demonstration. If haptic demonstration provides particularly precise information about target movements, the motor system's need for such information should more likely increase in the course of motor learning, in which case growing guidance should be more beneficial for learning. We contrasted fading and growing guidance in the course of learning a spatio-temporal motor pattern. To stimulate an active role of the learner, practice trials consisted of three phases, a visual demonstration of the target movement, a guided reproduction, and a reproduction without haptic guidance. Performance was assessed in terms of variable duration errors, relative-timing errors, variable path-length errors, and shape errors. Motor learning with growing and fading guidance turned out to be largely equivalent, so that the notion of an increasing optimal precision of haptic demonstrations, which matches a demand of increasingly precise information on the target movement, found no support. Duration errors declined only with fading, but not with growing guidance. Relative timing revealed a benefit of immediately preceding haptic demonstration, but learning was not different between the two practice protocols. This contrast between absolute and relative timing adds to other evidence according to which acquisition of these two aspects of motor timing involves different learning mechanisms. Whereas relative timing gained from immediately preceding haptic demonstration, but revealed no practice-related improvement in the presence of haptic guidance, the opposite pattern of results was found for the shape error. This finding is consistent with the claim that haptic demonstration is particularly efficient with respect to relative timing, but not with respect to spatial movement characteristics.