Human saccadic eye movements have three types of overshoot: dynamic overshoot, lasting 10-30 ms; glissadic overshoot, lasting 30-500 ms; and static overshoot, which is amended-after a delay of about 200 ms-by a subsequent corrective saccade. Glissades are the slow drifting eye movements occasionally seen at the end of saccadic eye movements. Glissades are hypothecated to be produced by mismatches in the pulse and step components of the motoneuronal controller signals. Glissades are not vergence eye movements, although the dynamics are similar.

Applications of robotics in surgery to date have taken advantage primarily of the robot's accurate positioning capability. Robotics technology could also be applied to a telerobotic microsurgical system with the surgeon dynamically controlling the manipulator. A first step toward developing such a system is to understand the surgeon's grasp and dexterous movement strategies. Principles of the analysis of grasp are described.<>

With major emphasis on simulation, a university laboratory telerobotics facility permits problems to be approached by groups of graduate students. Helmet-mounded displays provide realism; the slaving of the display to the human operator's viewpoint gives a sense of 'telepresence' that may be useful for prolonged tasks. Using top-down 3-D model control of distant images allows distant images to be reduced to a few parameters to update the model used for display to the human operator in a preview model to circumvent, in part, the communication delay. Also, the model can be used as a format for supervisory control and permit short-term local autonomous operations. Image processing algorithms can be made simpler and faster without trying to construct sensible images from the bottom. Control studies of telerobots lead to preferential manual control modes and, in this university environment, to basic paradigms for human motion and thence, perhaps, to redesign of robotic control, trajectory path planning, and rehabilitation prosthetics. Speculation as to future industrial drives for this telerobotic field suggests efficient roles for government agencies such as NASA.

Two experiments which are the beginning of a new effort to understand the phenomenon of sampling in hand tracking are described. The first measures subject responses to pulse inputs to test whether sampling is enforced by an input-triggered clock (such as a forced oscillator) or whether the sample period is determined by the time to process each movement, during which no further input is accepted. The second tests whether sampling is dependent on the direction of the target by giving successive steps in the same or opposite directions. It is found that the sampling does not appear to be enforced by a clock, and that the existence of a sampled response and its duration are direction dependent. it is hoped that these and future experiments, combined with results in the physiology literature, will produce a comprehensive model of the sampling mechanism.

Oscillations are a closed mystery to the non-mathematical biologist. In this paper, we review the application of control theory to a number of different oscillatory mechanisms in neurology.

An experimental telerobotics (TR) simulation is described suitable for studying human operator (HO) performance. Simple manipulator pick-and-place and tracking tasks allowed quantitative comparison of a number of calligraphic display viewing conditions. An enhanced perspective display was effective with a reference line from target to base, with or without a complex three-dimensional grid framing the view. This was true especially if geometrical display parameters such as azimuth (AZ) and elevation (EL) were arranged to be near optimal. Quantitative comparisons were made possible utilizing control performance measures such as root mean square error (rmse). There was a distinct preference for controlling the manipulator in end-effector Cartesian space for our primitive pick-and-place task, rather than controlling joint angles and then, via direct kinematics, the end-effector position. An introduced communication delay was found to produce decrease in performance. In considerable part, this difficulty could be compensated for by preview control information. That neurological control of normal human movement contains a sampled data period of 0.2 s may relate to this robustness of HO control to delay.

Accommodation dynamics have not been used in clinical diagnosis as have eye movement and pupillary dynamics; the difficulty of clinical observation is matched by limitations in measurement methods. An instrument suitable for clinical use is described that allows measurement of step response latencies and especially time constants. With computer analysis, phase plane trajectories, and noise spectra can be quickly obtained also. The utility of these dynamical parameters for clinical diagnosis is illustrated by a study of changes of time constants with age in prepresbyopia.

A two armed master-slave robot was modeled; simulations were run with a variety of compensation schemes using a payload with a compressive spring of 10,000 N/m and a preload force of 25 N against the payload. The slave arm was at first controlled by a simple linear force controller; this was inadequate with position step commands in that the force response oscillated greatly and resulted in crushing or dropping the payload. A low pass prefilter in the position command path corrected this, but so slowed the position response that significant tasks could not be carried out. These results illustrate the two way physical linkage between position output and force regulation dynamics. A second order, band pass cross filter sending position command as input into the forward loop of the force controller, enabled adequate position control dynamics and kept the payload force excursions to a minimum.

A model based on the theory of dynamical systems is proposed for the intrinsic random or pseudo-random mechanism underlying certain types of muscular tremor. The active length-tension curve of the individual sarcomere, in conjunction with the passive length-tension relation, is a map from length to tension with an observed time delay between length change and resulting tension change. The passive length-tension relation is assumed to relate this tension change back to a change in length instantaneously. The stability properties of this iterated interval map are investigated by means of computer simulation and computation of the Lyapunov exponent and the bifurcation tree. The resulting analysis is related to experimental tremor data in the literature in terms of period doubling, bifurcation points, and chaotic behavior. The model appears to have its most fruitful application in understanding the insect type and isometric mammalian types of tremor.< >

Vibration of agonist or antagonist muscle tendon produced changes in the triphasic electromyographic pattern of neck muscles; EMG signals were rectified, averaged, and also integrated by planimetry. The triphasic EMG envelopes obtained during fast horizontal head rotation showed unmodified early agonist pulse, the action pulse (PA), under all conditions; increased antagonist pulse, the braking pulse (PB), only with antagonist muscle vibration; and increase of late agonist pulse, the clamping pulse (PC), only with agonist muscle vibration. Vibration experiments can be considered as a model for studying interactions between central and peripheral effects on control of normal movements.

In fast (time-optimal) movements about many joint systems, the triphasic EMG pattern has been observed. Although the first agonist burst obviously initiates the movement, the roles of the second and third bursts, appearing in the antagonist and agonist respectively, have been less clear. In this study, the timing of experimentally measured EMG signals led to construction of a three-pulse control signal that produced an accurate simulation of experimentally measured time-optimal head rotations using a sixth-order nonlinear model in conjunction with an optimization algorithm. By ablating pulses from the model control signal and observing the resulting dynamics, the roles of the three pulses can be assessed. As a result, the pulses can be designated PA, the action pulse (for the first agonist burst), PB, the braking pulse (for the antagonist burst), and PC, the clamping pulse (for the second agonist burst). Comparison of dynamic parameters from the simulated movements revealed strategies used to generate control signals for movements of various speeds.

Ensemble averaging after pre-editing of surface EMG potentials has enabled construction of underlying controller signals from stereotyped head movements. Carefully controlled, intended time-optimal movements by trained, actively participating human subjects have been found to yield repeatable, multi-pulse controller signals. Also, adaptive changes in these horizontal head movements in response to added viscous loads showed further causal relationships between movement dynamics and EMG signals from left and right splenius muscles. These experimental results are a base from which modeling studies can be performed to explicate the neurological control strategies used in the performance of this class of movements.

Pupil responses to light are greatly influenced by initial pupil size. Small pupils, operating under photopic conditions, show tonic responses to step increases of light and high gains; thus the pupil is a good regulator of light. Large pupils, operating under mesopic or scotopic conditions show phasic responses, "pupillary escape", and smaller gains; the pupil only transiently influences retinal flux. By using accommodation level to set the size of the pupil, the mechanism of the "pupil size effect" is shown to be dependent on retinal light level only so far as retinal activity sets pupil size.

Pupillary escape has been described as an initial contraction followed by a slow redilatation, occurring in response to a step stimulus of low-intensity light. When the initial pupil size is small, the response to the same step stimulus is pupillary capture, a steady and sustained contraction. In this experiment a comparison was made between three modes of controlling pupil size and thereby of regulating the pupillary response: contralateral light background level, ipsilateral light background level, and accommodative level with which there is no change in retinal adaptation. All three level setting modes showed similar results in illustrating the pupil size effect. In addition, an inhibitory effect was found with both ipsilateral and contralateral light backgrounds that is independent of Weber's Law in the contralateral case. Our results lead to the formulation of a binocular model, featuring an internal parameter control whereby a signal dependent on the static pupil size regulates the gains of the parallel phasic and tonic pathways, the former responsive to transient changes of light, and the latter to background levels of light and accommodative levels. Our findings also raise interesting questions concerning the loci of these complex interactions in the simple neuroanatomy of the pupillary pathways.

A sixth order nonlinear model for horizontal head rotations in humans is presented and investigated using experimental results on head movement trajectories and neck muscle EMG. The controller signals, structured in accordance with time optimal control theory, are parameterized, and controller signal parameter variations show a dominating influence on different aspects of the head movement trajectory. The model fits the common head acceleration types over a wide range of amplitudes, and also less common (dynamic overshoot) trajectories.

A sixth order nonlinear model for horizontal head rotations in humans is analyzed using an extended parameter sensitivity analysis and a global optimization algorithm. The sensitivity analysis is used in both the direct sense, as a model fitting tool, and in the indirect sense, as a guide to experimental design. Resolution is defined in terms of the sensitivity table, and is used to interpret the sensitivity results. Using sensitivity analyses, the head and eye movement systems are compared and contrasted. Controller signal parameters are the most influential. Their variations and effects on head movement trajectories and accelerations are investigated, and the conclusions are compared with clinical neurological findings. The global optimization algorithm, in addition to automating the fitting of various types of data, is combined with time optimality theory to give theoretical time-optimal inputs to the model.

Voluntary nystagmus, a series of rapidly alternating saccadic eye movements accompanied by a failure of subjective stabilization of the visual world, was used to test the strength of relationship between subjective stabilization and saccadic suppression. Suppression of a full-field flash was similar during voluntary nystagmus and during voluntary saccades of the same magnitude (about 0.5 log unit threshold increase in each case) despite the difference in stabilization experienced in the two conditions. In a second experiment, the failure of subjects to perceive movement of a stabilized retinal image during voluntary nystagmus showed that no extraretinal signal was influencing apparent stimulus position. The results contradict the hypothesized role of saccadic suppression in subjective stabilization. The similarity of saccadic suppression during voluntary nystagmus and voluntary saccades (experiment 1) points out a significant similarity between the two types of eye movement, while the difference in subjective stabilization (experiment 2) reveals a significant distinction between them.

Glissades are the slow, gliding eye movements often appended to the end of human saccadic eye movements. They have been used as an aid in diagnosing disease states, eg, multiple sclerosis and vascular lesions. Glissades are a consequence of a mismatch between the sizes of the pulse and step components of the pulse-step motoneuronal controller signals. This physiological and simulation study shows that glissadic overshoot is caused by pulse width errors and not by pulse height errors. This implies that the CNS can control the firing frequencies and recruitment of motoneurons more precisely than it can control the duration of the high-frequency motoneuronal saccadic burst.

Dynamic measures of vergence accommodation (VG-ACC) are necessary for complete analysis of the triadic near response but are difficult to obtain because eyeball rotation affects accommodative measures. A dynamic optometer that uses the third Purkinje image is shown to be insensitive to small eye rotations and permits dynamic measures of VG-ACC responses. Such measures are presented to demonstrate the feasibility of this method. Average latency measures of 260 msec for VG-ACC fall between the latency of 160 msec for disparity vergence and the latency of 380 msec for accommodation. Additional dynamic features of VG-ACC resemble those of other components of the near triad.