The effect of visual transformation on bimanual circling movement.

In order to examine the effect of visual transformation on bimanual movements of various difficulty, fourteen participants performed bimanual circling tasks in three asymmetric movement modes--90 degrees (the left hand precedes the right hand by 1/4 cycle), 180 degrees (the delay between two hands is 1/2 cycle), and 270 degrees (the left hand precedes the right hand by 3/4 cycle)--under the normal vision condition and the visual transformation condition. In the visual transformation condition, movement of the right hand was transformed so that the required bimanual movement was always presented visually as a symmetric pattern. Additionally, the participants also performed a 0 degrees mode (in-phase symmetric) movement. Results revealed that the visual transformation increased the movement accuracy, with the variability of the right-left difference unchanged. Thus, proper visual transformation can improve the accuracy of a movement task. The 0 degrees mode was performed with higher stability and accuracy than any other movement modes of the visual transformation condition and normal vision conditions. In addition, the constant error associated with the 90 degrees and 270 degrees modes indicated that, in the normal vision condition, the executed movement was shifted to the 180 degrees mode, whereas in the visual transformation condition it stayed around the required mode and was slightly shifted to the 0 degrees mode. This result suggests that visual transformation can change the relationship between the intention to realize the required mode and the intrinsic neuromuscular dynamics. The effect size of visual transformation was larger in the 90 degrees and 270 degrees modes than in the 180 degrees mode. It is thus concluded that the effect of visual transformation depends upon the difficulty of the movement task.