PubMed Health⌕ Search

Biomedical subjects

P Morasso

Publications and source records attributed to P Morasso.

At least 19 recordsLinked to original sources
PubMed1988

Kinematic networks. A distributed model for representing and regularizing motor redundancy.

Motor control in primates relates to a system which is highly redundant from the mechanical point of view--redundancy coming from an imbalance between the set of independently controllable variables and the set of system variables. The consequence is the manifestation of a broad class of ill-posed problems, problems for which it is difficult to identify unique solutions. For example (i) the problem of determining the coordinated patterns of rotation of the arm joints for a planned trajectory of the hand; (ii) the problem of determining the distribution of muscle forces for a desired set of joint torques. Ill-posed problems, in general, require regularization methods which allow to spell acceptable, if not unique, solutions. In the case of the motor system, we propose that the basic regularization mechanism is provided by the potential fields generated by the elastic properties of muscles, according to an organizational principle that we call "Passive Motion Paradigm". The physiological basis of this hypothesis is reviewed and a "Kinematic Network" (K-net) model is proposed that expresses the kinematic transformations and the causal relations implied by elasticity. Moreover, it is shown how K-nets can be obtained from a kinematic "Body Model", in the context of a specific task. Two particularly significant results are: (i) the uniform treatment of closed as well as open kinematic chains, and (ii) the development of a new method for the automatic generation of kinematic equations with arbitrary topology. Moreover, the model is akin to the concept of "motor equivalence" in the sense that it provides families of motor equivalent trajectories parametrized by tunable motor impedances.

Biomechanical Phenomena↗
PubMed1983

Three dimensional arm trajectories.

Planar arm trajectories are characterized by a segmentation of the hand velocity profile and by a coupling between shape and speed. The question addressed in this paper is whether such coupling, observed in two dimensions, still holds in three dimensions. This matter was investigated experimentally by recording three dimensional "aimless" movements of the arm, particularly three dimensional scribbles, and the answer suggested by the experimental data is that only the "bending" of the trajectory is coupled with speed, whereas the "twisting" is independent of speed. The same behaviour was also found to characterize a computational model of trajectory formation which is based on the spatial composition of chains of planar strokes, overlapped in time.

Adult↗
PubMed1982

Trajectory formation and handwriting: a computational model.

This paper proposes a computational model for different aspects of trajectory formation, from point-to-point movements to handwriting. The proposed model is based on a mechanism of composition of basic curve elements (strokes) which separates the spatial and the temporal aspects of trajectory formation. At the same time, the model suggests a method for storing and describing arm movements, as a list of stroke descriptors. Experimental trajectories were digitized and analyzed with regard to several types of movements: i) point-to-point trajectories, ii) closed trajectories, iii) trajectories with inflection points, iv) spiral-like trajectories, v) handwritten trajectories. Velocity and curvature profiles were computed for the trajectories and the model was fitted to the data. The implications of the model and its "credibility" in the general context of motor control are discussed.

Arm↗
PubMed1982

Human arm trajectory formation.

In order to investigate the strategies used to plan and control multijoint arm trajectories, two-degrees-of-freedom arm movements performed by normal adult humans were recorded. Only the shoulder and elbow joints were active. When a subject was told simply to move his hand from one visual target to another, the path of the hand was roughly straight, and the hand speed profile of their straight trajectories was bell-shaped. When the subject was required to produce curved hand trajectories, the path usually had a segmented appearance, as if the subject was trying to approximate a curve with low curvature elements. Hand speed profiles associated with curved trajectories contained speed valleys or inflections which were temporally associated with the local maxima in the trajectory curvature. The mean duration of curved movements was longer than the mean for straight movements. These results are discussed in terms of trajectory control theories which have originated in the fields of mechanical manipulator control and biological motor control. Three explanations for the results are offered.

Adult↗
PubMed1981

Spatial control of arm movements.

Human subjects were instructed to point one hand to different visual targets which were randomly sequenced, using a paradigm which allowed two degrees of freedom (shoulder, elbow). The time course of the hand trajectory and the joint angular curves were observed. The latter exhibited patterns which change markedly for different movements, whereas the former preserve similar characteristics (in particular, a single peaked tangential velocity curve). The hypothesis is then formulated that the central command for these movements is formulated in terms of trajectories of the hand in space.

Adult↗
PubMed1980

Anthropomorphic robotics. I. Representing mechanical complexity.

A study of the fundamental principles upon which manipulation dexterity is based cannot help mixing robotic and neurophysiological concepts. A preliminary step in this study consists of trying to understand the complexity of manipulation dynamics. Though complexity shows itself in the massive number of elements of kinematic and dynamic equations, the fundamental simplicity of the underlying mechanical laws suggests to look for a structure, particularly from the computational point of view. Accordingly, a working computational model is proposed that organizes the massive computational load into a structure which is composed of a small number of computational units and lends itself to parallel computation.

Arm↗
PubMed1980

Anthropomorphic robotics. II. Analysis of manipulator dynamics and the output motor impedance.

An important factor in trying to capture the complexity of many manipulation problems is the notion of Output Motor Impedance, i.e., the relationship between a set of disturbing forces and the resulting variation in arm configuration. The functional significance of such force/displacement characteristics is investigated, showing how several aspects of different manipulation tasks (holding against gravity, inserting, fast moving, and throwing) can be naturally described in terms of appropriate modulation of the impedance characteristics of the manipulator. For this reason, impedance modulation can be considered an integral part of motor control.

Arm↗
PubMed1978

Effect of load disturbances during centrally initiated movements.

1. We have investigated the relative contributions of mechanical and reflex mechanisms in generating the forces produced by the neck muscles when loads were unexpectedly applied during centrally programmed head movements in monkeys. These movements, subserved by muscles well endowed with muscle spindles, are part of the coordinated eye-head response to the appearance of a stimulus in the animal's visual field. Our preparation was a chronically vestibulectomized monkey trained to make a visual discrimination. 2. Two procedures were used to evaluate the torque generated by the neck musculature when an unexpected load disturbance was applied: first, by surgically interrupting the afferent loop subserving the reflex action (section of cervical dorsal roots) and second, by building a mathematical model of the head-neck system and carrying out a process of simulation. 3. Our results indicated that the compensatory torque of reflex origin stimulated by the application of an opposing force was less than 10--30% of that required for perfect compensation, and the larger fraction of the observed compensation was due to the mechanical properties (inertial, viscous, and elastic) of the neck musculature. The combined action of reflex and mechanical processes never completely compensated for the disturbance.

Animals↗
PubMed1977

The use of mini- and micro-computers in eye clinical practice.

In an ophthalmological department there are many sectors in which the use of computers can give useful support. We have singled out three major areas of interest: 1. the rationalization of the flow of patients; 2. the management of clinical records; 3. the automatization of ophthalmological devices. Instead of using different dedicated computational systems we preferred to focus our attention on a unique system based on a minicomputer driving several parallel micro-processors. Preliminary results are given.

Computers↗
PubMed1976

Mechanisms underlying achievement of final head position.

The studies reported here are directed toward understanding some of the mechanisms whereby the central nervous system terminates a given phase in a motor sequence and maintains a newly acquired position. In particular, we investigated the extent to which the termination of a centrally initiated head movement in monkeys and the subsequent maintenance of posture depend on a readout of proprioceptive afferent input generated during the movement itself or are instead centrally programmed. We approached this question in two ways: first, using vestibulectomized, but otherwise intact monkeys, we applied load disturbances unexpectedly at the beginning and throughout centrally initiated head movements with the aim of provoking a proprioceptive response in all types of neck receptors and to observe the outcome of this stimulation on the head final position. In a second set of experiments, we interrupted the flow of afferent input by cutting cervical and upper thoracic dorsal roots and observed how the absence of proprioceptive feedback affects the achievement of final head position. The results indicated that the central pattern of neural impulses establishing final head position is preprogrammed and it is not reset by the afferent proprioceptive impulses generated during the intended movement. In addition, our findings are consistent with the view that final head position is an equilibrium point dependent on a number of factors, such as the firing rate and the recruitment of the alpha motoneurons, the length-tension properties of the muscles involved in posture, and passive elastic properties of external loads.

Animals↗