Pietro G. Morasso

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The present paper examines human hand impedance characteristics, including inertia and viscosity as well as stiffness, in multi-joint arm movements. While a subject maintains a given hand location, small external disturbances are applied to his hand by a manipulandum. The corresponding force-displacement vectors are measured and sampled over time in order(More)
A stiffness control model for the stabilization of sway has been proposed recently. This paper discusses two inadequacies of the model: modeling and empiric consistency. First, we show that the in-phase relation between the trajectories of the center of pressure and the center of mass is determined by physics, not by control patterns. Second, we show that(More)
In order to identify useful guidelines for the clinical practitioner as regards the use of static posturographic analysis, we collected a set of posturograms from 3 groups of participants (normal participants, Parkinsonian patients, and osteo-porotic patients), according to the Romberg test. From each posturogram, we extracted global parameters (in the time(More)
The main purpose of this study is to compare two different feedback controllers for the stabilization of quiet standing in humans, taking into account that the intrinsic ankle stiffness is insufficient and that there is a large delay inducing instability in the feedback loop: 1) a standard linear, continuous-time PD controller and 2) an intermittent PD(More)
The paper presents a control model of body sway in quiet standing, which aims at achieving bounded stability by means of an intermittent control mechanism. Control bursts are generated when the current state vector exits an area of uncertainty around the reference point in the phase plane. This area is determined by the limited resolution of proprioceptive(More)
In this study, we describe a device for the direct measurement of intrinsic ankle stiffness in quiet standing. It consists of a motorised footplate mounted on a force platform. By generating random sequences of step-like disturbances (1 degrees amplitude, 150 ms duration) and measuring the corresponding displacements of the center of pressure in the(More)
The sway-density curve (SDC) is computed by counting, for each time instant, the number of consecutive samples of the statokinesigram falling inside a circle of small radius R. The authors evaluated the sensitivity of the curve to the variation of R and found that in the range 3-5 mm the sensitivity was low, indicating that SDC is a robust descriptor of(More)
This communication addresses again the hypothesis that the stabilization of balance during quiet standing is achieved by the stiffness of ankle muscles without anticipatory active control. It is shown that a recently proposed method of estimating ankle stiffness directly from the analysis of the posturographic data is incorrect because it ignores the(More)
This paper reviews different approaches for explaining body sway while quiet standing that directly address the instability of the human inverted pendulum. We argue that both stiffness control [Winter, D. A., Patla, A. E., Riedtyk, S., & Ishac, M. (2001). Ankle muscle stiffness in the control of balance during quiet standing. Journal of Neurophysiology, 85,(More)
Cerebellar symptoms are extremely disabling and are common in Multiple Sclerosis (MS) subjects. In this feasibility study, we developed and tested a robot therapy protocol, aimed at the rehabilitation of incoordination in MS subjects. Eight subjects with clinically defined MS performed planar reaching movements while grasping the handle of a robotic(More)