Proceedings of The Physiological Society
Cardiff University (2009) Proc Physiol Soc 17, C18
A study of ankle proprioception using compensatory tracking
M. Lakie1, T. M. Osborne1, R. F. Reynolds1, I. Loram2
1. School of Sport and Exercise Sciences, Birmingham, Birmingham, United Kingdom. 2. Institute of Research into Movement, Manchester Metropolitan, Manchester, United Kingdom.
In compensatory tracking a subject is required to realign a target which is moved by the experimenter. Unlike pursuit tracking, where the target and the subject’s response are separately displayed, the subject experiences only the combined effect of disturbance and correction - steering a boat buffeted by side-winds is a simple example. The ability to continuously attempt to correct for an offset in this way is not unique to the visual system, for example in nulling disturbances to posture in order to maintain an upright stance corrective responses may be informed by vestibular or proprioceptive senses as well as vision. Despite this, little work appears to have been carried out on compensatory tracking using non-visual senses. With ethical permission, nine subjects were positioned in a normal standing position while strapped to a backboard. Their feet rested on a footplate which was subjected to computer controlled antero-posterior perturbations with a size and frequency like exaggerated standing sway. The subject was supplied with a joystick which also controlled footplate angle. After appropriate practice the subjects were instructed to attempt to correct for the computer disturbances using only the information from their ankles, so that as far as possible ankle movement was minimized. Four trials were conducted with the intended position of the foot horizontal and four with the intended position 2 degrees of dorsiflexion. For comparison four trials were conducted with visual information only. In two of these the visual information was by foveation of a fiducial marker, in the other two a looming target provided more “ecological” information akin to visual flow in standing. All subjects were generally poor compensators. The worst performance was using proprioception with feet horizontal. The best was with explicit visual information. Increased dorsiflexion appeared to be better than feet horizontal. Proprioceptive tracking and “ecological” visual tracking were intermediate (Fig1). The mean delays in the subjects’ responses were calculated by cross-correlation. Regression analysis showed that the subjects with the longest delays tended to be the poorest compensators. We conclude that delay and insensitivity to very slow perturbations (drift) combine to severely impair effective compensation.
Where applicable, experiments conform with Society ethical requirements