A color-contingent prism displacement aftereffect

Mapping shape to visuomotor mapping: learning and generalisation of sensorimotor behaviour based on contextual information

Humans can learn and store multiple visuomotor mappings (dual-adaptation) when feedback for each is provided alternately. Moreover, learned context cues associated with each mapping can be used to switch between the stored mappings. However, little is known about the associative learning between cue and required visuomotor mapping, and how learning generalises to novel but similar conditions. To investigate these questions, participants performed a rapid target-pointing task while we manipulated the offset between visual feedback and movement end-points. The visual feedback was presented with horizontal offsets of different amounts, dependent on the targets shape. Participants thus needed to use different visuomotor mappings between target location and required motor response depending on the target shape in order to "hit" it. The target shapes were taken from a continuous set of shapes, morphed between spiky and circular shapes. After training we tested participants performance, without feedback, on different target shapes that had not been learned previously. We compared two hypotheses. First, we hypothesised that participants could (explicitly) extract the linear relationship between target shape and visuomotor mapping and generalise accordingly. Second, using previous findings of visuomotor learning, we developed a (implicit) Bayesian learning model that predicts generalisation that is more consistent with categorisation (i.e. use one mapping or the other). The experimental results show that, although learning the associations requires explicit awareness of the cues' role, participants apply the mapping corresponding to the trained shape that is most similar to the current one, consistent with the Bayesian learning model. Furthermore, the Bayesian learning model predicts that learning should slow down with increased numbers of training pairs, which was confirmed by the present results. In short, we found a good correspondence between the Bayesian learning model and the empirical results indicating that this model poses a possible mechanism for simultaneously learning multiple visuomotor mappings.

Dual adaptation to sensory conflicts during whole-body rotations

A dual adaptation paradigm was used in order to study the adaptation to two conditions of conflicting visual and kinesthetic and vestibular information. Adaptation was induced in humans by modifying visual information during whole-body rotations with the help of a virtual reality set-up. Real rotations' amplitudes were factored by a gain of 0.5 or 1.5. The two conditions were associated to a visual context cue. The aim of the experiment was to provide support for either the feedback or the feedforward model of adaptive states switch. Results show that subjects could adapt to the two conditions of conflict during whole-body rotations. However, the two conflict situations have been found to differ both in their motor dynamics and in their susceptibility to adaptation, as it seems that the adaptation is more complete in the condition of gain 1.5, i.e., faster and more precise. Subjects could be divided into two groups according to their ability to use contextual information to switch between adaptive gains. The visual cues were sufficient for some subjects to switch adaptive state, which corresponds to a context-dependent dual adaptation, or feedforward model of switching. Other subjects showed a switch cost maintained across the experiment, corresponding with a stimulus-dependent adaptation, or feedback model of switching. We are suggesting that the process enabling switching between adaptive states depends on subjects' abilities to use contextual cues of certain types, and thus on their "perceptive styles". This could explain the variability of results obtained in the literature.

Context-dependent arm pointing adaptation

We sought to determine the effectiveness of head posture as a contextual cue to facilitate adaptive transitions in manual control during visuomotor distortions. Subjects performed arm pointing movements by drawing on a digitizing tablet, with targets and movement trajectories displayed in real time on a computer monitor. Adaptation was induced by presenting the trajectories in an altered gain format on the monitor. The subjects were shown visual displays of their movements that corresponded to either 0.5 or 1.5 scaling of the movements made. Subjects were assigned to three groups: the head orientation group tilted the head towards the right shoulder when drawing under a 0.5 gain of display and towards the left shoulder when drawing under a 1.5 gain of display; the target orientation group had the home and target positions rotated counterclockwise when drawing under the 0.5 gain and clockwise for the 1.5 gain; the arm posture group changed the elbow angle of the arm they were not drawing with from full flexion to full extension with 0.5 and 1.5 gain display changes. To determine if contextual cues were associated with display alternations, the gain changes were returned to the standard (1.0) display. Aftereffects were assessed to determine the efficacy of the head orientation contextual cue compared to the two control cues. The head orientation cue was effectively associated with the multiple gains. The target orientation cue also demonstrated some effectiveness while the arm posture cue did not. The results demonstrate that contextual cues can be used to switch between multiple adaptive states. These data provide support for the idea that static head orientation information is a crucial component to the arm adaptation process. These data further define the functional linkage between head posture and arm pointing movements.