Extraction of Traditional COP-Based Features from COM Sway in Postural Stability Evaluation.

Postural control during quiet standing is traditionally evaluated by analyzing CoP sway measured by using a force platform. However, recent proliferation of motion tracking systems made available an estimate of the CoM location. Traditional CoP-based measures presented in literature provide information about age-related changes in postural stability and fall risk. We investigated, on an age-matched group of subjects, the relationship between classical CoP-based measures computed on sway path and statistical mechanics parameters on diffusion plot, with those extracted from CoM time-series. Our purpose is to understand which of these parameters, computed from CoM sway, can discriminate postural abnormalities, in order to use a video tracking system to evaluate balance in addition to motor capabilities.

A New Tool for Investigating the Functional Testing of the VOR

Peripheral vestibular function may be tested quantitatively, by measuring the gain of the angular vestibulo-ocular reflex (aVOR), or functionally, by assessing how well the aVOR performs with respect to its goal of stabilizing gaze in space and thus allow to acquire visual information during the head movement. In recent years, several groups have developed clinical and quantitative approaches to functional testing of the vestibular system based on the ability to identify an optotype briefly displayed on screen during head rotations. Although the proposed techniques differ in terms of the parameters controlling the testing paradigm, no study has thus far dealt with understanding the role of such choices in determining the effectiveness and reliability of the testing approach. Moreover, recent work has shown that peripheral vestibular patients may produce corrective saccades during the head movement (covert saccades), yet the role of these eye movements toward reading ability during head rotations is not yet understood. Finally, no study has thus far dealt with measuring the true performance of their experimental setups, which is nonetheless likely to be crucial information for understanding the effectiveness of functional testing approaches.Thus we propose a new software and hardware research tool allowing the combined measurement of eye and head movements, together with the timing of the optotype on screen, during functional testing of the vestibulo-ocular reflex (VOR) based on the Head ImpulseTest.The goal of such tool is therefore that of allowing functional testing of the VOR while collecting the experimental data necessary to understand, for instance, (a) the effectiveness of the covert saccades strategy toward image stabilization, (b) which experimental parameters are crucial for optimizing the diagnostic power of the functional testing approach, and (c) which conditions lead to a successful reading or an error trial

Dynamics of Learning in the Open Loop VORXIII Mediterranean Conference on Medical and Biological Engineering and Computing 2013

We present our preliminary results on motor adaptation of the angular vestibulo-ocular reflex (aVOR) in response to passive impulsive head rotations at constant acceleration (460 deg/s2). Human healthy subjects were repeatedly subjected to a 20 degrees yaw rotation (using a rotating chair) while they tried to maintain fixation on a visual target. We used an incremental velocity error signal in which target moved partially with the head, during rotations, causing adaptation of the initial eye velocity. We analyzed only the first 100 msec of the aVOR, i.e. the open loop portion of the response. In order to better understand the multiple-timescales dynamics of motor learning subjects were adapted to a aVOR gain reduction period followed by a shorter reverse adaptation block of trials, and a subsequent no-error feedback period which caused a recovery toward the initially adapted state. Adaptation mechanisms have been successfully described using a two hidden states model, in which a fast state learns quickly from motor error, but has poor retention, and a slow state that learns slowly but has a stronger retention. We modeled our data using such two-states model finding an underestimation of the spontaneous recovery trend

Multiple timescales in the adaptation of the rotational VOR

Goal-directed movements, such as pointing and saccades, have been shown to share similar neural architectures, in spite of the different neuromuscular systems producing them. Such structure involve an inverse model of the actuator being controlled, which produces the commands innervating the muscles, and a forward model of the actuator, which predicts the sensory consequences of such commands and allows online movement corrections. Recent studies have shown that goal-directed movements also share similar motor-learning and motor-memory mechanisms, which are based on multiple timescales. The hypothesis that also the rotational vestibulo-ocular reflex (rVOR) may be based on a similar architecture has been presented recently. We hypothesize that multiple timescales are the brain's solution to the plasticity-stability dilemma, allowing adaptation to temporary and sudden changes while keeping stable motor-control abilities. If that were the case, then we would also expect the adaptation of reflex movements to follow the same principles. Thus we studied rVOR gain adaptation in eight healthy human subjects using a custom paradigm aimed at investigating the existence of spontaneous recovery, which we considered as the hallmark of multiple timescales in motor learning. Our experimental results show that spontaneous recovery occurred in six of eight subjects. Thus we developed a mathematical model of rVOR adaptation based on two hidden-states processes, which adapts the cerebellar-forward model of the ocular motor plant, and show that it accurately simulates our experimental data on rVOR gain adaptation, whereas a single timescale learning process fails to do so

Development of an automatic evaluation system for balance assessment scales

The problem of a correct fall risk assessment is becoming more and more impelling with the increasing elderly population. However, despite this fact, no new tools have been developed to improve the ability to predict fall risk in individual patients and the clinical assessment procedures are based on subjective scoring of clinical balance scales. This work documents our current effort to develop a novel method to inspect balance control through a system for the automatic evaluation of exercises drawn from balance assessment scales. Our aim is to overcome classical limits found in these scales i.e. limited granularity and inter-/intra-rater reliability, to obtain objective scores and more detailed information allowing to predict fall risk

Affordable, automatic quantitative fall risk assessment based on clinical balance scales and Kinect data

The problem of a correct fall risk assessment is becoming more and more critical with the ageing of the population. In spite of the available approaches allowing a quantitative analysis of the human movement control system’s performance, the clinical assessment and diagnostic approach to fall risk assessment still relies mostly on non-quantitative exams, such as clinical scales. This work documents our current effort to develop a novel method to assess balance control abilities through a system implementing an automatic evaluation of exercises drawn from balance assessment scales. Our aim is to overcome the classical limits characterizing these scales i.e. limited granularity and inter-/intra-examiner reliability, to obtain objective scores and more detailed information allowing to predict fall risk. We used Microsoft Kinect to record subjects' movements while performing challenging exercises drawn from clinical balance scales. We then computed a set of parameters quantifying the execution of the exercises and fed them to a supervised classifier to perform a classification based on the clinical score. We obtained a good accuracy (~82%) and especially a high sensitivity (~83%)