Figure 6. Instantaneous mutual orientation of kinaesthetic and visual frames and trajectory generation.

(a): screen visualisation of the intended movement towards the target (blue circle) using the cursor (red circle); (b): wrist movement in order to reach the target in different experimental conditions. The curved path wrist movement are mapped on the screen rotated according the visuomotor transformation. The inability of the subject to move the wrist along the desired direction d_kin, which would correspond to the straight path to the target d_vis, is caused by the lack of capacity in mentally rotating the kinaesthetic-wrist-centered FR_KIN to macth the visual-virtual-reality FR_VIS map. (c): orientation of the visual-environment frame FR_VIS, the kinaesthetic-wrist-centered frame FR_KIN and the head-centerd frame FR_H during a pointing movement in different experimental conditions. The aiming error is due to the instantaneous angular mismatch between the two frames of reference.