Effects of vestibular and oculomotor stimulation on responsiveness of the carotid-cardiac baroreflex.

Twelve healthy men underwent measurement of their carotid-cardiac baroreflex response during varying conditions of vestibulo-oculomotor stimulation to test the hypothesis that vestibular and/or oculomotor stimulation associated with head movements in the yaw plane inhibit baroreflex control of heart rate. We assessed the carotid-cardiac baroreflex response by plotting R-R intervals (in milliseconds) at each of eight neck pressure steps with their respective carotid distending pressures (in millimeters mercury). Baroreflex sensitivity was measured under four experimental conditions: 1) sinusoidal whole body yaw rotation of the subject in the dark without visual fixation (combined vestibular-oculomotor stimulation); 2) yaw oscillation of the subject while tracking a small head-fixed light moving with the subject (vestibular stimulation without eye movements); 3) subject stationary while fixating on a small light oscillating in yaw at the same frequency, peak acceleration, and velocity as the chair (eye movements without vestibular stimulation); and 4) subject stationary in the dark (no eye or head motion).

Application of robust data processing methods to the analysis of eye movements.

We have developed a robust, nonlinear differentiating digital filter for the estimation of eye velocity from an eye-position signal. This filter is equally applicable to a large variety of other biomedical signals. The filter is implemented by taking an odd number of two-point differences around the point of interest and then selecting the median difference.

Effects of cerebellar lesions on saccade simulations.

Experimental studies involving cerebellar lesions have been important tools for learning about the operation of the saccadic eye movement system. These studies have been used to further develop a neural network model for horizontal saccadic eye movement control. The neural control mechanism is first order time optimal, initiated by the deep layers of the superior colliculus and terminated by the cerebellar fastigial nucleus.

Simulation of oculomotor post-inhibitory rebound burst firing using a Hodgkin-Huxley model of a neuron.

A number of theories have been reported on post saccade phenomenon describing dynamic overshoot, glissadic overshoot and undershoot, and undershoot, all naturally and frequently occurring saccadic eye movements. Electrophysiological evidence for post-inhibitory rebound burst firing activity during saccadic eye movements is prevalent in the literature. However, the cause for the phenomenon is not known.

Eye tracking performance variability in a homogeneous population.

Pursuit tracking eye movements were recorded and analyzed from a group of US Air Force Pilot Candidates (PCs). The PCs ranged in age from 21 to 27 with a median age of 23. All were college graduates and recently passed a Flying Class I physical exam.

The application of smooth pursuit eye movement analysis to clinical medicine.

Pursuit tracking eye movements were analyzed from selected patients with neurological injuries and compared to the responses of 20 normal subjects. The patients/subjects tracked a small spot of light moving sinusoidally in the horizontal plane at a frequency of 0.4 Hz and a peak-to-peak amplitude of 40 degrees.

Nonlinear approaches for separation of slow and fast phase nystagmus signals.

Central nervous system (CNS) disorders and vestibulo-ocular reflex (VOR) degradation contribute to the loss of orientation and balance, typically causing the illusion of motion. VOR degradation may be caused by illnesses or common prescription medications, and this degradation may have serious repercussions in affecting one's ability to walk, maintain balance, or track moving objects. The two current VOR analysis techniques are applied to nystagmus signals (recordings of eye position during standardized tests) to isolate the two neuronal pathways used.

Analysis of pursuit tracking eye movements in pilots and nonfliers.

Pursuit tracking eye movements were recorded and analyzed from a group of Air Force pilots and a group of nonflying Air Force members. The tracking performance of the pilots was compared to the performance of the nonfliers. Subjects tracked a small spot of light moving sinusoidally in the horizontal plane at frequencies ranging from 0.

Linear systems analysis of the vestibulo-ocular reflex: clinical applications.

We used whole-body angular acceleration stimuli to estimate the transfer function of the vestibuloocular reflex in 20 normal subjects and several patients. Eye movements evoked by the stimuli were recorded and an adaptive nonlinear digital filter was used to extract the compensatory component of the eye-movement response. Frequency domain analysis of the stimulus and the compensatory component of the response was used to estimate the transfer function.

Selecting a stimulus signal for linear systems analysis of the vestibulo-ocular reflex.

We evaluated 3 types of stimulus signals for use in estimating the transfer function of the vestibulo-ocular reflex. We used individual sine-wave, sum-of-sine, and pseudorandom stimuli. Five normal human subjects were tested 5 times each using each of the 3 stimulus types.

A comparison of static and dynamic characteristics between rectus eye muscle and linear muscle model predictions.

The characteristics of a muscle model are analyzed using rectus eye muscle parameter values and compared to rectus eye muscle data. The muscle is modeled as a viscoelastic parallel combination connected to a parallel combination of active state tension generator, viscosity element, and length tension elastic element. Each of the elements is linear and their existence is supported with physiological evidence.

Relationships between manual reaction time and saccade latency in response to visual and auditory stimuli.

Manual reaction time (RT) responses were analyzed from seven human subjects. Responses were recorded using four kinds of target presentations: fixed visual target, moving visual target, fixed auditory target, and moving auditory target. Moving targets (moving in the horizontal plane) were presented at constant intensity and provided only a motion cue.

Optimization of an adaptive nonlinear filter for the analysis of nystagmus.

An adaptive nonlinear digital filter has been designed for the analysis of an eye-movement signal called nystagmus. Nystagmus is a bi-phasic signal consisting of a sequence of tracking eye movements called "slow-phase" interspersed with brief, high-velocity refixation movements called "fast-phase." The objective of the analysis is to separate the nystagmus signal into its fast- and slow-phase components.

Saccades simulated with rhesus monkey innervation data.

Extracellular single-unit data from the vicinity of the abducens nucleus from rhesus monkeys recorded during horizontal saccades are used as input to an updated oculomotor plant to simulate saccades to test the robustness of the model. Cells recorded from include: Long Lead Burst neurons, Medium Lead Burst neurons, and Burst Tonic neurons. Eye movement position data was collected using the magnetic coil technique.

Digitally calibrated eye movement measurement system.

A less expensive instrumentation alternative to record horizontal eye movements is presented in the form of a feasibility study. Currently, there are several techniques used to accurately measure eye position for research purposes. To implement these techniques, significant financial resources are required.

A new approach to the analysis of nystagmus: an application for order-statistic filters.

A computer program has been designed for the analysis of nystagmus. This program employs a class of nonlinear digital filters called order-statistic (OS) filters. Two OS filters and one linear filter are used.

Periodic saccadic oscillations and tinnitus.

A man with essential hypertension developed stereotyped cycles of oscillopsia and bilateral "sparking" tinnitus. Eye movement recordings showed cycles of disconjugate opsoclonus, square-wave jerks, and saccadic dynamic overshoot disrupting stable fixation. Neuroimaging studies were normal.

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.

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).

Additional developments in oculomotor plant modeling.

A new oculomotor plant is presented in this study using an updated third-order linear muscle model. The lateral and medial rectus muscle is modeled as a viscoelastic parallel combination connected to a parallel combination of active state tension generator, viscosity element and length tension elastic element. The eyeball is modeled as a sphere, connected to two parallel viscoelastic elements, connected in series.

Development of a non-linear smoothing filter for the processing of eye-movement signals.

The analysis of eye-movement (EM) signals poses problems for the designer of smoothing filters since many of the interesting types of EMs are bimodal. For example, optokinetic and/or vestibular stimulation results in an EM pattern called nystagmus consisting of alternating fast- and slow-phase components. Also, saccadic (refixation) EMs do not occur continuously, but are interspersed with periods of fixation.

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.

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.

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.

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.