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Biomedical subjects

E J Engelken

Publications and source records attributed to E J Engelken.

At least 37 records · Page 2Linked to original sources
PubMed1990

Temporal characteristics of saccadic eye movements induced by auditory stimuli.

Records of horizontal saccadic eye movements made in response to auditory stimuli in the absence of any target related visual stimuli were obtained from two normal human subjects. A band-limiting derivative filter was convolved with records of eye position to obtain estimates of eye velocity. Eye position and velocity records were analyzed off-line to determine the characteristics of the audio-ocular response (AOR). The latency of the AOR decreased with increasing target movement amplitude. The AOR also exhibited lower peak velocity and longer duration than previously reported visually induced saccades. The time at peak velocity increased as saccade amplitude increased until for eye movements with amplitudes greater than 15 degrees, time at peak velocity showed little further increase. Finally, the AOR displayed a high incidence of dynamic overshoot for abducting movements of the right eye and a low incidence of dynamic overshoot for adducting movements of the right eye. System parameters estimated using system identification techniques indicate that the pulse portion of the active state tension driving the agonist muscle is of lower magnitude for auditory saccades than for visual saccades.

Eye Movements↗
PubMed1990

Sensitivity analysis of human oculomotor muscle model.

Sensitivity analysis is a procedure for examining the importance of model parameters with respect to the input or output of the model. Presented is a sensitivity analysis of a recently updated fourth order linear homeomorphic oculomotor model. Each muscle is modeled as a viscoelastic parallel combination connected to an active state tension generator, viscosity element and length tension element parallel combination. The eyeball is modeled as a sphere with a moment of inertia which is connected to two voight elements in series. The sensitivity analysis revealed the parameters of the model obtained from mathematical analysis are acceptable to be used as nominal parameters. Consequently, the analytical parameters can vary considerably while allowing the model to perform as empirical data predicts.

Elasticity↗
PubMed1989

Stochastic variables responsible for observed saccadic variability.

A new stochastic local feedback model of the horizontal saccadic system based on time optimal neural control within the superior colliculus has been previously described. This model uses a premotor neural circuit composed of burst, tonic, and pause cells and innervates a fourth order linear homeomorphic muscle plant. A sequence of saccades recorded from human subjects shows great variability in peak velocity, final position, and amount and type of post-saccadic behavior. This variability is duplicated in a sequence of simulated saccades through the use of random variables within the neural circuitry. The random variables are agonist burst cell magnitude, antagonist post inhibitory rebound burst magnitude and timing, and to a lesser extent muscle saturation magnitude. These four random variables are shown to cause all the observed variability in human saccades, including: trajectory profile, velocity profile, dynamic overshoot, and glissadic overshoot and undershoot.

Eye Movements↗
PubMed1989

Computer analysis of smooth pursuit eye movements.

Smooth-pursuit eye movements are analyzed using a system analysis approach. Frequency domain methods are used to factor the smooth-pursuit response into a linear component and a nonlinear or remnant component. The linear component is that part of the tracking response that is linearly related to the target movement; the remnant is the component remaining after the linear component is subtracted out. Tracking abnormalities that are not evident by inspection of the complete eye-movement record become obvious upon inspection of the remnant.

Computers↗
PubMed1989

Neurosignal analysis during saccadic eye movements.

An inverse method is developed to investigate the oculomotor neural control signal. The oculomotor plant is modeled with a fourth-order linear homeomorphic saccadic eye movement model. Parameter estimation is performed using a conjugate gradient search method which minimizes the integral of the absolute value of the error squared between the model and the data. Derivatives are computed using band-limited differentiation (BLD) techniques and the results are compared to derivatives computed using the two-point central difference method. Using the BLD technique allows for greater flexibility in choosing a cutoff frequency, provides true low-pass filtering above the cutoff frequency, and gives more consistent results than using the two-point central difference method. The input to the oculomotor plant model is computed. The input is a cumulative force consisting of the agonist and antagonist active state tensions and their respective rate-of-change terms. The agonist force is also determined by approximating the antagonist active state tension and removing if from the cumulative input force.

Electrooculography↗
PubMed1989

A linear muscle model predicts the hyperbolic force-velocity relationship.

A variety of different schemes have been reported in the literature for linearizing the force-velocity relationship observed in muscle, a dominant element in the muscle. This report extends assertions that a linear muscle system has force-velocity characteristics as described by Hill's hyperbolic equation, and that no linearization whatsoever is required. The muscle is modeled as a parallel combination of passive elasticity, and series elasticity connected to the parallel combination of active state tension generator, viscosity and length tension elasticity. Each of the elements are linear. Simulation solutions of this third-order system yield a hyperbolic shaped force-velocity curve using physiologically derived estimates, based on the oculomotor system, for the parameters of the muscle model.

Elasticity↗
PubMed1989

Agonist and antagonist muscle tension during horizontal saccadic eye movements.

Agonist and antagonist muscle tension simulations are reported for a fourth-order model of the oculomotor plant and active state tensions generated by a neural feedback model during horizontal saccadic eye movements. The lateral and medial rectus muscles are modeled as a parallel combination of passive elasticity, and series elasticity connected to a parallel combination of active state tension generator, viscosity element and elastic element. The eyeball is modeled as a sphere with moment of inertia connected to a viscosity element and an elastic element. The active state tension is generated by a low-pass filtered output from the neural burst circuit. The saccade generator is first-order time optimal and located in the superior colliculus. Agonist muscle tensions simulated with TUTSIM match the data extremely well. Antagonist muscle tension simulated with TUTSIM have an initial drop in tension, consistent with microelectrode predictions, and then a rise in muscle tension. The initial drop in antagonist muscle tension has not been reported in the literature because of band limitations of the force transducer used to record muscle tension.

Computer Simulation↗
PubMed1989

Saccadic eye movements in response to visual, auditory, and bisensory stimuli.

Saccadic eye movements were recorded and analyzed from eight normal human subjects. Various visual, auditory, and bisensory (visual and auditory) targets were tracked. Primary saccade latency, amplitude, duration, and peak velocity were calculated, as well as overall saccade duration (total time spent making saccades) and final eye position. Saccades made to bisensory targets employing a constant-intensity auditory component were not different from the pure visual target responses. Saccades to bisensory targets having an intermittent auditory component (with sound onset synchronous with the visual component) demonstrated a significant reduction in latency (11.3%) compared to the visual responses. The reduction occurred both for a fixed overhead sound source and for a sound source moving with the visual component. This result indicates that providing an auditory motion or localization cue alone does not reduce latency, but that a sound onset cue facilitates response time. No other response parameters were enhanced by using bisensory targets.

Acoustic Stimulation↗
PubMed1986

Single sinusoids compared with a multiple-sinusoids technique for evaluating horizontal semicircular canal function.

The vestibulo-ocular reflex (VOR) of 162 normal subjects was evaluated using two rotational testing procedures. Data from 79 subjects were collected using a set of five single-frequency stimuli (0.01 to 0.16 Hz) and 83 subjects were tested using multifrequency stimuli (0.01 to 0.27 Hz). The use of multifrequency stimuli in place of single frequencies reduced testing time from 75 min to 20 min per subject. The diagnostically useful phase response of the VOR, as estimated by the two tests, were not statistically different. Equivalent phase measures may be obtained within a shorter testing period using the multifrequency procedure.

Acceleration↗
PubMed1981

Symposium on low frequency harmonic acceleration, the rotatory chair. Responses to low-frequency harmonic acceleration in patients with acoustic neuromas.

There has been increased interest in harmonic acceleration (HA) for the evaluation of vestibular pathology in recent years. The purpose of this study was to determine the value of harmonic acceleration testing in 24 patients with surgically proven acoustic neuromas. All patients were tested preoperatively and postoperatively, and none were lost to follow-up. Thirteen were tested one year or more after surgery. For rotational evaluation, each patient was seated in an enclosed chair driven by a D.C. torque motor turntable system and rotated utilizing five low frequency sinusoids (.01 - .16 Hz). Slow eye movements in response to acceleration were analyzed by analog and digital computer techniques. Output measures were the phase relationships between the input stimulus velocity and the slow phase eye movement velocity and labyrinthine preponderance (LP) or asymmetry. Preoperative results showed that caloric examination identified 79% of patients with tumors and HA 67% (2 standard deviation criteria). When both tests were evaluated together they identified 91% of all patients with tumors. Of the 4 small tumors (less than 2 cm), HA identified 4 and caloric examination 2. All patients were tested approximately 7 days postoperatively and had statistically significant shifts in their phase and LP measures. The shifts in phase were stable up to 3 years after surgery; however, the LP returned toward normal values. These findings indicate that the vestibular system can compensate but not repair itself after the loss of one labyrinth. In those patients who continued to be symptomatic 1 year or more after surgery, the LP did not return to normal values. Harmonic acceleration testing complemented caloric testing in the identification of patients with tumors and objectively demonstrated patients with continued symptomatology after surgery.

Acceleration↗
PubMed1979

Low-frequency harmonic acceleration in the evaluation of surgical treatment of Meniere's disease.

23 patients with classical findings of Meniere's disease and so diagnosed by a neurotologist were tested with harmonic acceleration. 7 of these patients were selected to receive endolymphatic-mastoid shunts for intractable vertigo and/or highly progressive fluctuant hearing loss. All 7 patients showed an increase in the impairment in their phase relationships at the lowest frequency (0.01Hz) following surgery which was considered to be secondary to the procedure. Later this phase lag returned to a level approaching normal. They also showed a definite decrease in the asymmetry (labyrinthine preponderance) of their nystagmic responses to acceleration.

Acceleration↗
PubMed1979

A modeling approach to the assessment of smooth pursuit eye movement.

We have proposed a quasilinear model of the oculomotor system in the performance of a smooth pursuit tracking task. Model parameters (gain, phase, and spectral purity) have been measured for 21 normal subjects at stimulus frequencies of 0.2, 0.4, 0.8, 1.2, and 1.6 Hz. The normal oculomotor system was found to be quite linear when tracking at the three lowest frequencies, with up to 95% of the output power being linearly correlated with the input stimulus. Data from patients with known pathology are presented to demonstrate model parameter sensitivity to oculomotor dysfunction.

Adolescent↗
PubMed1977

Analog processing of vestibular nystagmus for on-line cross- correlation data analysis.

An analog processing circuit is described which allow accurate measurement of the phase relationships between input angular acceleration and resulting eye velocity. Vestibular nystagmic data are processed via analog technics to yield slowphase eye velocity. The turntable velocity input is cross-correlated with the eye velocity output, using a Nicolet MED-80 minicomputer system. The resulting correlograms are further processed to obtain precise phase information. Test data analysis shows a system resolution within 1 degree. Data from human and animal subjects are portrayed.

Acceleration↗