Motor Variability but Functional Specificity: The Case of a C4 Tetraplegic Mouth Calligrapher

Abstract

This study examined the movement coordination in an exceptional tetraplegic individual who has practiced Japanese calligraphy with a mouth-held brush for over 25 years to reach master level. In the experiment, the calligrapher wrote the same Chinese character on a sheet of ink paper multiple times. The uncontrolled manifold analysis revealed the forms of covariation among joint degrees of freedom so as to keep the brush pressure, brush angle, and upright head posture invariant over different realizations of the task while allowing for joint configuration fluctuations that do not affect these task variables. The fact that the 3 task variables were simultaneously controlled further suggested that the acquisition of the skill was not only a matter of learning to control each of the task variables but also a matter of learning to nest different layers of activities that control the multiple functional relationships to the environment in such a way as not to be dysfunctional for one layer to another.

Notes

¹This result does not mean that the particular values of the task variables were kept constant within one trial but that at each of the 23 events, across-trial variance was structured in such a way as to leave each task variable invariant.