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Biomedical subjects

F E Guedry

Publications and source records attributed to F E Guedry.

At least 19 recordsLinked to original sources
PubMed1998

Motion sickness and development of synergy within the spatial orientation system. A hypothetical unifying concept.

Adaptation to research paradigms such as rotating rooms and optical alteration of visual feedback during movement results in development of perceptual-motor programs that provide the reflexive assistance that is necessary to skilled control of movement and balance. The discomfort and stomach awareness that occur during the adaptation process has been attributed to conflicting sensory information about the state of motion. Vestibular signals depend on the kinematics of head movements irrespective of the presence or absence of signals from other senses. We propose that sensory conflict when vestibular signals are at least one component of the conflict are innately disturbing and unpleasant. This innate reaction is part of a continuum that operates early in life to prevent development of inefficient perceptual-motor programs. This reaction operates irrespective of and in addition to reward and punishment from parental guidance or goal attainment to yield efficient control of whole body movement in the operating environment of the individual. The same mechanism is involved in adapting the spatial orientation system to strange environments. This conceptual model "explains" why motion sickness is associated with adaptation to novel environments and is in general consistent with motion sickness literature.

Adaptation, Physiological↗
PubMed1997

Vertical optokinetic nystagmus and after-responses during backward tilt.

METHOD: Vertical optokinetic nystagmus (VOKN) and after-responses were detected in nine subjects using the corneo-retinal potential (CRP) technique and an infrared video camera detection apparatus (ISCAN) simultaneously. The ISCAN method produced a much smaller inter-subject variability, a higher linear regression coefficient (0.94) when vertical eye position was regressed against vertical target position (+/- 30 degrees, 5 degrees increments). Detected by ISCAN, VOKN responses were measured at 3 angles of pitch head (and body) tilt: upright (0 degrees), supine (90 degrees), and declined 45 degrees below horizontal (135 degrees). Two stripe velocities (40 degrees.s-1 and 60 degrees.s-1) were used. RESULTS: In six of the nine subjects (67%) and in 40/54 conditions (74%) for all subjects, upward (slow phase velocity up) VOKN gain was greater than downward VOKN gain for both stripe velocities at all tilt angles. The gain for both upward and downward VOKN decreased as stripe velocity increased from 40-60 degrees.s-1, which suggests that both upward and downward VOKN systems were starting to saturate. Across subjects, a mean up-down asymmetry index, I, increased monotonically as the subjects declined. The slope of the monotonic function was greater for 60 degrees.s-1 stripe velocity than for 40 degrees.s-1 stripe velocity. The mean of all subjects' individual asymmetry ratios (ASYM) also increased as tilt increased but the slope of the best fitted regression line was not statistically significantly different from zero (p > 0.05). CONCLUSION: Optokinetic after-responses observed in the present study were of two types: 1) resetting of the eye by a drift, with nystagmus superimposed, from a beating field (eye position) that occurred during optokinetic stimulation; and 2) resetting of the eye without nystagmus superimposed. Upward VOKN produced the greatest number of after-responses. The beating field of VOKN was not correlated with pitch tilt.

Adult↗
PubMed1996

Spatial orientation perception and reflexive eye movements--a perspective, an overview, and some clinical implications.

When head motion includes a linear velocity component, eye velocity required to track an earth-fixed target depends upon: a) angular and linear head velocity, b) target distance, and c) direction of gaze relative to the motion trajectory. Recent research indicates that eye movements (LVOR), presumably otolith-mediated, partially compensate for linear velocity in small head excursions on small devices. Canal-mediated eye velocity (AVOR), otolith-mediated eye velocity (LVOR), and Ocular Torsion (OT) can be measured, one by one, on small devices. However, response dynamics that depend upon the ratio of linear to angular velocity in the motion trajectory and on subject orientation relative to the trajectory are present in a centrifuge paradigm. With this paradigm, two 3-min runs yields measures of: LVOR differentially modulated by different subject orientations in the two runs; OT dynamics in four conditions; two directions of "steady-state" OT, and two directions of AVOR. Efficient assessment of the dynamics (and of the underlying central integrative processes) may require a centrifuge radius of 1.0 meters or more. Clinical assessment of the spatial orientation system should include evaluation of central integrative processes that determine the dynamics of these responses.

Eye Movements↗
PubMed1992

Perception of motion and position relative to the earth. An overview.

Results of the five experiments are consistent with the following generalizations. Canal-mediated turn perception (pitch, roll, or yaw) in earth-horizontal or earth-vertical plane, is suppressed in direct relationship to the magnitude of a linear acceleration vector lying in the plane of a responding canal when the magnitude of the linear vector is constant or increasing and when its direction is either fixed or rotating in the same direction as the concomitant canal signal. Canal-mediated turn perception (pitch, roll, or yaw) is not suppressed by a coplanar linear vector that is counterrotating relative to the canal signal. Change in perceived attitude (pitch, roll, or yaw) is very sluggish in the absence of concordant canal information; attitude change may not be an immediate otolith-mediated perceptual event but a slowly developing perception dependent upon cognitive appreciation of an immediate otolith angular position signal. Otolith phasic neural units, unreinforced by appropriate canal signals, may contribute more to a brief linear velocity component in perception than to rate of attitude change. Otolith-mediated attitude perception within a given earth-vertical plane can be distorted by strong coplanar angular velocity canal information. Once distorted, return to veridical attitude perception can be gradual because, in the absence of complimentary canal or visual information, recovery is dependent upon relatively slow cognitive appreciation of a prevailing otolith position signal. Several attractive hypotheses relating to the dynamics of attitude perception can only be tested by substantially more data on the dynamics of spatial orientation perception. Most of our objectives cannot be achieved without models that yield valid prediction of the dynamics of spatial orientation perception. All of the observations in these experiments were carried out in darkness, or, in the simulated catapult experiment, without external visual reference. Various forms of visual information will change the dynamics of spatial orientation perception. My discussion has been limited to consideration of the vestibular system, as though the canal and otolith systems completely controlled the dynamics of spatial orientation perceptions. Obviously other partners in the dynamics of postural control, including vision, proprioception, and expectation, must be included in this challenging field of research. Dedication to stereotyped ideas about objectivity in the 20th century has hindered advancement of knowledge on the dynamics of spatial orientation perception relative to rate of progress achieved by several scientists of the 18th and 19th centuries, who provided word pictures of perceived motions and tilts along with descriptions of the motions that engendered the pictures.(ABSTRACT TRUNCATED AT 400 WORDS)

Gravitation↗
PubMed1992

The dynamics of spatial orientation during complex and changing linear and angular acceleration.

The dynamics of spatial orientation perception were examined in a series of experiments in which a total of 43 subjects were passively exposed to various combinations of linear and angular acceleration during centrifuge runs. Perceptual effects during deceleration were much stronger than effects during acceleration. The dynamics of spatial orientation perception differed substantially from changes in the vestibulo-ocular reflex (VOR). VOR was fairly well predicted by a current model, but our experiments revealed perceived change in attitude (roll, pitch, yaw tilt position in space) and perceived angular velocity in space that was not reflected by parallel changes in the plane or magnitude of the VOR. This series of experiments establishes several facts concerning spatial orientation perception beyond the predictive domain of any current model. New concepts are needed and several are suggested to deal with changing reactions to complex combinations of linear and angular accelerations.

Acceleration↗
PubMed1991

Steady state and transient G-excess effects.

Acceleration forces of flight are associated with a number of spatial orientation illusory effects. This note focuses on two effects, both called the "G-excess effect." A distinction between steady-state and transient G-excess effects is important because prescriptions for preventive management of effects in flight will differ.

Acceleration↗
PubMed1988

The influence of active versus passive head oscillation, and mental set on the human vestibulo-ocular reflex.

We compared passive (manual) whole body, and active head oscillation in normal human subjects attempting mentally to influence the vestibulo-ocular reflex (VOR). Our objective was to establish simple procedural guidelines for vestibular test procedures in clinical settings. Using a head-fixed target, both methods of oscillation yielded virtually zero gain. Using an Earth-fixed target, active oscillation gain was unity, while passive gain was slightly less than 1. Using an imagined Earth-fixed target in the dark, both active and passive gains were reduced considerably, but passive gain was reduced more. Using an imagined head-fixed target in the dark, VOR gain was near zero at low frequencies but increased as frequency increased. Again, passive gain was less than active gain. At frequencies above 1 Hz, VOR gain in all conditions approached a value between 0.7 and 0.9. We conclude that active and manual passive rotation are simple and effective methods to test the VOR, but emphasize that visual and mental influences must be carefully controlled.

Adult↗
PubMed1988

Performance-based assessment of oculomotor efficiency.

Acquisition of visual information from spatial points disparate enough to necessitate head and eye movement involves the vestibular and other oculomotor control systems in shifting and stabilizing gaze relative to those points. In the present study, a simple procedure to test oculomotor abilities was developed and evaluated; it uses performance (serial letter identification) to maintain initial gaze position and performance (number of digits correctly identified) to measure the efficiency of gaze-shift control. Number of digits acquired from briefly displayed digit sets was consistently and powerfully influenced by exposure duration of digit sets and to a lesser extent by the size of required gaze shift. The performance of normal subjects in eye movement and head-and-eye movement conditions is predictable from static performance of normals. Results suggest that the procedure will be sensitive to certain types of central nervous system and vestibular pathology. Substantial individual differences in performance dependent upon gaze-shift control were found among normal subjects. If some pilots operate at the lower extremes of the performance distribution, they may be subject to critical response deficiencies in emergency conditions requiring large gaze shifts.

Adult↗
PubMed1987

Aerobic fitness and susceptibility to motion sickness.

Susceptibility to motion sickness was evaluated in 29 males having high, moderate, and low levels of aerobic fitness. Subjects underwent Coriolis (cross-coupled) vestibular stimulation on a Stille-Werner rotator during a 10 min modification of the Brief Vestibular Disorientation Test (BVDT). Variables evaluated were: spin time before aborting (ST), heart rate (HR), respiratory rate (RR), mean skin temperature (Tsk), subject observation values (SV), and observation values (OV). Aerobic fitness and ST for the total population were inversely related (r = -0.506, p less than 0.01). Difference in ST was significant (F(2.26) = 6.67, p less than 0.01), with the high aerobic group demonstrating an earlier ST and greater SV than the low aerobic group (Student-Newman-Keuls; alpha = 0.05). Analysis of HR, RR, and Tsk between groups revealed limited differences. Based on these data, men with high aerobic fitness appear to have an increased susceptibility to motion sickness.

Heart Rate↗
PubMed1983

Modification of per- and postrotational responses by voluntary motor activity of the limbs.

In order to explore interactive effects of voluntarily generated rotational stimuli on evoked vestibular responses, experiments were performed using a rotation chair in which the subject either controlled the angular motion by voluntary movement of his upper and lower limbs, or was passive-rotation being controlled by a servomotor and electromagnetic brake. In two experiments, carried out on 8 and 9 subjects respectively, it was found that cessation of sustained passive rotation by voluntary limb actions strongly suppressed the postrotational turning sensation but did not alter the evoked nystagmus. Limb movements that were directionally concordant with muscle torque in generating body rotation yielded arthrokinetic effects which augmented perrotational nystagmus and sustained the sensation of turning. The postrotational sensation of turning and postrotational nystagmus produced by voluntary cessation of active rotation were reduced relative to responses produced by passive turning and stopping. The Purkinje effect induced by postrotational head movements was similarly reduced following voluntary cessation of active rotation.

Adult↗
PubMed1982

The vestibulo-ocular reflex in man during voluntary head oscillation under three visual conditions.

The vestibulo-ocular reflex (VOR) generated by voluntary head movements keyed to a tone varying sinusoidally in pitch was studied in 13 men. Modulation of pitch at frequencies ranging from 0.1-5.0 Hz yielded systematic variation in head movement frequencies, although above 2 Hz head frequencies fell below requested frequencies. Three conditions of visual stimulation were used. When an Earth-fixed visual target was visible, VOR gain (maximum eye velocity/maximum head velocity) was slightly but significantly greater than VOR gain in darkness at all frequencies except 0.1 Hz. With a head-fixed target, VOR gain was substantially less than VOR gain in darkness at all requested frequencies below 2.0 Hz. The finding that visual suppression becomes ineffective at frequencies above 1.0 Hz parallels results obtained in other laboratories during passive whole-body oscillation. Results indicate that the procedures are feasible for further evaluation as part of a clinical test battery.

Acceleration↗
PubMed1982

Apparent instrument horizon deflection during and immediately following rolling maneuvers.

There have been recent reports by pilots of apparent visual bending or bowing of instrument horizons during and immediately following ascending rolling maneuvers in the F-14 aircraft. The present study investigates the probability that normal reflex actions may partially account for the illusions cited in these reports. The results of this study suggest that the vestibulo-ocular reflex (VOR) can produce an apparent deflection of the instrument horizon (actually an apparent flicking back and forth) during and after roll maneuvers involving high peak angular velocities. This perceptual aberration could disturb a pilot attempting to use his instrument horizon and could lead him to suspect instrument malfunction. The reported distortions of the instrument horizon could be the result of the VOR, which tends to stabilize the eye relative to the Earth during angular acceleration of the head, and therefore reflexly displaces the eye relative to objects such as flight instruments that move with the head.

Acceleration↗
PubMed1982

Influence of a visual display and frequency of whole-body angular oscillation on incidence of motion sickness.

Visual search within a head-fixed display consisting of a 12 X 12 digit matrix is degraded by whole-body angular oscillation at 0.02 Hz (+/- 155 degrees/s peak velocity), and signs and symptoms of motion sickness are prominent in a number of individuals within a 5-min exposure. Exposure to 2.5 Hz (+/- 20 degrees/s peak velocity) produces equivalent degradation of the visual search task, but does not produce signs and symptoms of motion sickness within a 5-min exposure.

Acceleration↗
PubMed1981

Visual-vestibular interactions: the directional component of visual background movement.

Legibility of a head-fixed display and visual suppression of the vestibulo-ocular reflex (VOR) were found to be superior when vestibular stimuli and optokinetic stimuli were of like direction (i.e. would produce the same directions of nystagmus) and inferior when they were opposite in direction. Velocities (relating to the head) of peripheral optokinetic stimuli ranging between -18 degrees/s and +180 degrees/s interacted effectively with vestibular stimuli to influence visibility of a head-fixed display. This indicates that peripheral optokinetic stimulation can influence visual suppression of the VOR at velocities that far surpass effective production of optokinetic nystagmus.

Electronystagmography↗
PubMed1979

Visual-vestibular interactions: I. Influence of peripheral vision on suppression of the vestibulo-ocular reflex and visual acuity.

Legibility of head-fixed displays in some motion environments is partially dependent upon visual suppression of the vestibuloocular reflex (VOR). This study investigates the effects of differing relationships between peripheral background movement and whole-body motion on the VOR and on visual performance. The purpose of the study is to explore factors in motion environments that influence performance limits and to develop procedures of potential usefulness in evaluating interacting visual and vestibular function. Visual performance and visual suppression of the VOR were markedly different, depending upon the relative direction of peripheral background movement. Visual suppression of the VOR, and visual performance, were disrupted far more when vestibular inputs and peripheral optokinetic inputs were discordant than when they were concordant. Results have potential implications for head-up displays and suggest a procedure for evaluating visual/vestibular function.

Acceleration↗
PubMed1978

Coriolis cross-coupling effects: disorienting and nauseogenic or not?

Nausea and disorientation are sometimes produced by head movements during turning maneuvers in aircraft. These responses are usually attributed to Coriolis cross-coupling stimulation of the vestibular system, although it has been indicated recently that many turning maneuvers of aircraft have insufficient angular velocity to generate such effects. The purpose of the present study was to further distinguish conditions in which Coriolis cross-coupling effects are disorienting and nauseogenic from conditions in which they are neither.

Adult↗
PubMed1978

Visual counteraction on nauseogenic and disorienting effects of some whole-body motions: a proposed mechanism.

It has been indicated that the nauseogenic and disorienting effects of several kinds of provocative motion stimuli can be ameliorated by visual reference to the Earth. The purpose of the present experiment is to investigate a hypothesis concerning the mechanism of this beneficial effect. The results demonstrate that the aftereffects of large-field optokinetic stimulation can nullify the nauseogenic and disorienting effects of Coriolis cross-coupled vestibular stimuli. It is hypothesized that large-field optokinetic stimulation in a particular head plane modifies activity in the vestibular nuclei as though the semicircular canals in that plane had been stimulated. A previous study illustrated that such semicircular canal stimulation would completely nullify the disturbing and disorienting effects of Coriolis cross-coupled stimulation according to theoretical expectations. The results provide inferential support for the hypothesis and suggest that predictability of disorientation and nauseogenic disturbance is reasonably well handled by current theory when the conditions of motion are fairly well specified.

Adult↗