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Biomedical subjects

J W Wolfe

Publications and source records attributed to J W Wolfe.

At least 19 recordsLinked to original sources
PubMed1988

Frequency response analysis of human saccadic eye movements: estimation of stochastic muscle forces.

A frequency response method is used to estimate parameters of a fourth-order model of the oculomotor system and the active state tensions during a saccadic eye movement. The lateral and medial rectus muscle of each eye is modeled as a parallel combination of an active state tension generator with a viscosity and elastic element, connected to a series elastic element. The eyeball is modeled as a sphere connected to a viscosity and elastic element. Each of these elements is assumed to be ideal and linear. The active state tension for each muscle is modeled by a low-pass filtered pulse-step waveform. Initial estimates of the oculomotor mechanical components are based on physiological evidence. Initial estimates of the active state tension are based on an extrapolation of the eye movement trajectory. Horizontal saccadic eye movements were recorded from infrared signals reflected from the anterior surface of the cornea and then digitized. Parameter estimates were calculated for the model by using a conjugate gradient search program which minimizes the integral of the absolute value of the squared error between the model and the data. The predictions of the model are shown to be in good agreement with the data. Final estimates of motoneuronal activity demonstrate that the agonist muscle is maximally stimulated during the early portion of a saccadic eye movement regardless of the amplitude of the saccade; only the duration of the maximal stimulation affects the size of the saccade. The antagonist muscle is completely inhibited during the period of maximum agonist muscle stimulation. Furthermore, it is demonstrated that saccade motoneuronal activity is a stochastic phenomenon.

Elasticity↗
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↗
PubMed1979

Application of linear system analysis to the horizontal vestibulo-ocular reflex of the alert rhesus monkey using pseudorandom binary sequence and single frequency sinusoidal stimulation.

Horizontal eye movements of the alert rhesus monkey resulting from both pseudorandom binary sequence (PRBS) and single frequency sinusoidal rotational stimulation were analyzed using a PDP 11/40 computer in order to generate gain, phase, and coherence estimates at discrete frequencies between 0.008 and 1.28 Hz. A computer simulation of vestibular induced eye movements was used to validate our analysis procedures and to determine the effects of digital noise. Frequency domain transfer functions derived from gain and phase estimates revealed that the responses to PRBS stimulation and to single frequency sinusoids were not appreciably different. PRBS testing was accomplished in approximately one third the time required for sinusoidal testing and yielded highly reproducible data. We conclude that PRBS stimulation is a reliable and efficient method for assessing linear system parameters of the horizontal vestibulo-ocular reflex. PRBS testing may be particularly advantageous in studies of vestibulo-oculomotor plasticity in which rapid assessment of alterations in system dynamics is essential.

Animals↗
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

Functional linkage between the electrical activity in the vermal cerebellar cortex and saccadic eye movements.

The temporal relation between the onset of electrical activity of Purkinje cells and the occurrence of rapid eye movements was studied. Experiments were performed in unanesthetized animals, the recordings being made under direct vision through the use of a chronically implanted teflon sleeve. The following results were obtained. 1. Correlation between the activity of Purkinje cells and eye movements indicates that Purkinje cell firing in vermal lobules VI and VII precedes eye movement by 11-12 msec, peak activity corresponding to the time of onset of eye movement. 2. This eye movement related activity of Purkinje cells occurred regardless of the direction of the eye movements but some cells showed directional biases. Best correlation between eye movement and Purkinje cell activity was found with fast eye movements toward the right regardless of recording side. 3. Electrical activity of Purkinje cells was mainly related to saccades. Slow eye movement modulation, although probably present, was not studied in detail. 4. In those cells where an extensive set of measurements could be made, Purkinje cell firing was found to be inversely proportional to the amplitude of the eye movement, small movements being preceded by highest Purkinje cell activity. The present results suggest that cerebellar vermis responds prior to the generation of eye movement and may probably serve to control eye movements in a ballistic manner.

Animals↗
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↗