The uncontrolled manifold concept: identifying control variables for a functional task

• Published in: Experimental brain research 1999-06, Vol.126 (3), p.289-306
• Main Authors: SCHULZ, J. P, SCHÖNER, G
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Biomechanical Phenomena; Central Nervous System - physiology; Fundamental and applied biological sciences. Psychology; Gravitation; Hand - physiology; Head - physiology; Humans; Joints - physiology; Models, Biological; Motor Activity - physiology; Motor control and motor pathways. Reflexes. Control centers of vegetative functions. Vestibular system and equilibration; Posture - physiology; Space life sciences; Vertebrates: nervous system and sense organs
• ISSN: 0014-4819; 1432-1106
• DOI: 10.1007/s002210050738

The degrees of freedom problem is often posed by asking which of the many possible degrees of freedom does the nervous system control? By implication, other degrees of freedom are not controlled. We give an operational meaning to "controlled" and "uncontrolled" and describe a method of analysis through which hypotheses about controlled and uncontrolled degrees of freedom can be tested. In this conception, control refers to stabilization, so that lack of control implies reduced stability. The method was used to analyze an experiment on the sit-to-stand transition. By testing different hypotheses about the controlled variables, we systematically approximated the structure of control in joint space. We found that, for the task of sit-to-stand, the position of the center of mass in the sagittal plane was controlled. The horizontal head position and the position of the hand were controlled less stably, while vertical head position appears to be no more controlled than joint motions.