A Robotic Device for Measuring Human Ankle Motion Sense

Abstract

Proprioceptive signals about ankle motion are essential for the control of balance and gait. However, objective, accurate methods for testing ankle motion sense in clinical settings are not established. This study presents a fast and accurate method to assess human ankle motion sense acuity. A one degree-of-freedom (DOF) robotic device was used to passively rotate the ankle under controlled conditions and applied a psychophysical forced-choice paradigm. Twenty healthy participants were recruited for study participation. Within a trial, participants experienced one of three <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">reference</i> velocities (10°/s, 15°/s, and 20°/s), and a smaller <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">comparison</i> velocity. Subsequently, they verbally indicated which of the two movements was faster. As outcome measures, a just-noticeable-difference (JND) threshold and interval of uncertainty (IU) were derived from the psychometric stimulus-response difference function for each participant. Our data show that mean JND threshold increased almost linearly from 0.53°/s at the 10°/s <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">reference</i> to 1.6°/s at 20°/s ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> < 0.0001). Perceptual uncertainty increased similarly (median IU = 0.33°/s at 10°/s and 0.97°/s at 20°/s; <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> < 0.0001). Both measures were strongly correlated ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> = 0.70). This implies that the bias of the human ankle motion sense is approximately 5 - 8% of the experienced movement velocity. We demonstrate that this robot-aided test produces quantitative data on human ankle motion sense acuity. It provides a useful addition to the current measures of ankle proprioceptive function.