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Biomedical subjects

L R Young

Publications and source records attributed to L R Young.

At least 55 records · Page 3Linked to original sources
PubMed1987

Influence of visual and motion cues on manual lateral stabilization.

The ability of humans to detect and control their own lateral acceleration was measured by means of a closed-loop nulling task. Wide-field moving visual cues enhanced the operator's performance in nulling self-motion, especially at lower frequencies. Even visual cues, fixed relative to the operator, resulted in performance improvement relative to self-motion nulling in the dark. Describing function (frequency response) data was obtained for random acceleration conditions consisting of the visual field fixed relative to the laboratory, fixed relative to the subject, moving at constant velocity relative to the subject, and in the dark. The describing function data was corrected for the dynamics of operator manual control strategy. The resulting frequency responses were used to develop a linear model of self-motion detection which required a lead term of 1.5 rad.s-1 to be added to the existing model in order to match the higher sensitivity at higher frequencies.

Acceleration↗
PubMed1987

Normative study of Spacelab preflight/postflight vestibular test battery.

A study was designed to establish baseline normative responses to the MIT/Canadian Spacelab vestibular test battery. Three tests used a linear acceleration sled to measure otolith function: 1) perception of linear motion (threshold determination); 2) compensatory eye movements (linear VOR); 3) closed-loop nulling, in which the blindfolded subject nulls his velocity with a joystick under the influences of a pseudorandom sled disturbance. Rotational VOR was measured at 0.3 and 0.8 Hz in the dark and the light. Static visual-vestibular interaction was tested with a standard rod and frame apparatus, while dynamic interaction was assessed by susceptibility to roll vection induced by a rotating peripheral visual field. Two examples are presented of how results from this study can aid in the interpretation of data from preflight/postflight testing of Space Shuttle/Spacelab crews on these same experiments.

Adult↗
PubMed1986

M.I.T./Canadian vestibular experiments on the Spacelab-1 mission: 1. Sensory adaptation to weightlessness and readaptation to one-g: an overview.

Experiments on human spatial orientation were conducted on four crewmembers of Space Shuttle Spacelab Mission 1. This introductory paper presents the conceptual background of the project, the relationship among the experiments and their relevance to a "sensory reinterpretation hypothesis". Detailed experiment procedures and results are presented in the accompanying papers in this series. The overall findings are discussed in this article as they pertain to the following aspects of hypothesized sensory reinterpretation in weightlessness: utricular otolith afferent signals are reinterpreted as indicating head translation rather than tilt, sensitivity of reflex responses to footward acceleration is reduced, and increased weighting is given to visual and tactile cues in orientation perception and posture control. Three subjects developed space motion sickness symptoms, which abated after several days. Head movements, as well as visual and tactile cues to orientation influenced symptoms in a manner consistent with the sensory-motor conflict theory of space motion sickness. Six short duration tests of motion sickness susceptibility, conducted pre-flight, failed to predict sickness intensity in weightlessness. An early otolith-spinal reflex, measured by electromyography from the gastrocnemius-soleus muscles during sudden footward acceleration, was inhibited immediately upon entering weightlessness and declined further during the flight, but was unchanged from pre-flight when measured shortly after return to earth. Dynamic visual-vestibular interaction was studied by measuring subjective roll self-motion created by looking into a spinning drum. Results suggest increased weighting of visual cues and reduced weighting of graviceptor signals in weightlessness. Following the 10 day flight, erect posture with eyes closed was disturbed for several days.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1986

M.I.T./Canadian vestibular experiments on the Spacelab-1 mission: 2. Visual vestibular tilt interaction in weightlessness.

Adaptation to weightlessness includes the substitution of other sensory signals for the no longer appropriate graviceptor information concerning static spatial orientation. Visual-vestibular interaction producing roll circularvection was studied in weightlessness to assess the influence of otolith cues on spatial orientation. Preliminary results from four subjects tested on Spacelab-1 indicate that visual orientation effects were stronger in weightlessness than pre-flight. The rod and frame test of visual field dependence showed a weak post-flight increase in visual influence. Localized tactile cues applied to the feet in space reduced subjective vection strength.

Adaptation, Physiological↗
PubMed1986

M.I.T./Canadian vestibular experiments on the Spacelab-1 mission: 5. Postural responses following exposure to weightlessness.

The four science crewmembers of Spacelab-1 were tested for postural control before and after a 10 day mission in weightlessness. Previous reports have shown changes in astronaut postural behavior following a return to earth's 1-g field. This study was designed to identify changes in EMG latency and amplitudes that might explain the instabilities observed post-flight. Erect posture was tested by having the subject stand on a pneumatically driven posture platform which pitched rapidly and unexpectedly about the ankles causing dorsi- and plantarflexion. Electromyographic (EMG) activity from the tibialis anterior and the gastrocnemiussoleus muscles was measured during eyes open and eyes closed trials. The early (pre 500 ms) EMG response characteristics (latency, amplitude) in response to a disturbance in the posture of the subject were apparently unchanged by the 10 days of weightlessness. However, the late (post 500 ms) response showed higher amplitudes than was found pre-flight. General postural control was quantitatively measured pre- and post-flight by a "sharpened Romberg Rails test". This test showed decrements in standing stability with eyes closed for several days post-flight.

Adaptation, Physiological↗
PubMed1986

M.I.T./Canadian vestibular experiments on the Spacelab-1 mission: 6. Vestibular reactions to lateral acceleration following ten days of weightlessness.

Tests of otolith function were performed pre-flight and post-flight on the science crew of the first Spacelab Mission with a rail-mounted linear acceleration sled. Four tests were performed using horizontal lateral (y-axis) acceleration: perception of linear motion, a closed loop nulling task, dynamic ocular torsion, and lateral eye deviations. The motion perception test measured the time to detect the onset and direction of near threshold accelerations. Post-flight measures of threshold and velocity constant obtained during the days immediately following the mission showed no consistent pattern of change among the four crewmen compared to their pre-flight baseline other than an increased variability of response. In the closed loop nulling task, crewmen controlled the motion of the sled and attempted to null a computer-generated random disturbance motion. When performed in the light, no difference in ability was noted between pre-flight and post-flight. In the dark, however, two of the four crewmen exhibited somewhat enhanced performance post-flight. Dynamic ocular torsion was measured in response to sinusoidal lateral acceleration which produces a gravitionertial stimulus equivalent to lateral head tilt without rotational movement of the head. Results available for two crewmen suggest a decreased amplitude of sinusoidal ocular torsion when measured on the day of landing (R+0) and an increasing amplitude when measured during the week following the mission.

Acceleration↗
PubMed1984

Spatial orientation in weightlessness and readaptation to earth's gravity.

Unusual vestibular responses to head movements in weightlessness may produce spatial orientation illusions and symptoms of space motion sickness. An integrated set of experiments was performed during Spacelab 1, as well as before and after the flight, to evaluate responses mediated by the otolith organs and semicircular canals. A variety of measurements were used, including eye movements, postural control, perception of orientation, and susceptibility to space sickness.

Acceleration↗
PubMed1984

On the predictive control of foveal eye tracking and slow phases of optokinetic and vestibular nystagmus.

Smooth pursuit and saccadic components of foveal visual tracking as well as more involuntary ocular movements of optokinetic (o.k.n.) and vestibular nystagmus slow phase components were investigated in man, with particular attention given to their possible input-adaptive or predictive behaviour. Each component in question was isolated from the eye movement records through a computer-aided procedure. The frequency response method was used with sinusoidal (predictable) and pseudo-random (unpredictable) stimuli. When the target motion was pseudo-random, the frequency response of pursuit eye movements revealed a large phase lead (up to about 90 degrees) at low stimulus frequencies. It is possible to interpret this result as a predictive effect, even though the stimulation was pseudo-random and thus 'unpredictable'. The pseudo-random-input frequency response intrinsic to the saccadic system was estimated in an indirect way from the pursuit and composite (pursuit + saccade) frequency response data. The result was fitted well by a servo-mechanism model, which has a simple anticipatory mechanism to compensate for the inherent neuromuscular saccadic delay by utilizing the retinal slip velocity signal. The o.k.n. slow phase also exhibited a predictive effect with sinusoidal inputs; however, pseudo-random stimuli did not produce such phase lead as found in the pursuit case. The vestibular nystagmus slow phase showed no noticeable sign of prediction in the frequency range examined (0 approximately 0.7 Hz), in contrast to the results of the visually driven eye movements (i.e. saccade, pursuit and o.k.n. slow phase) at comparable stimulus frequencies.

Eye Movements↗
PubMed1982

Human ocular counterrolling induced by varying linear accelerations.

Ocular counterrolling (OCR) has previously been studied using static head tilt or continuous rotation about the line of sight as a stimulus to the otolith organs. This study presents the first measurements of OCR in humans induced by linear accelerations. Dynamic measurements of the response to lateral linear acceleration indicate the eye movements to be on the order of 2 degrees for 0.2 g peak acceleration, 0.2 Hz sinusoidal acceleration. These values are consistent with static OCR studies. The dynamics of the response are similar to a low order linear system with a dominant time constant of 0.33 s. A previous model predicts a time constant of 0.32 s. Sinusoidal oscillation at 0.2, 0.4, and 1.0 Hz with a 0.2 g peak acceleration showed good agreement with the model in both gain and phase. The question of amplitude linearity remains unsettled. This otolithocular reflex, over short periods at least, appears to be stationary in the statistical sense.

Acceleration↗
PubMed1981

Influence of combined visual and vestibular cues on human perception and control of horizontal rotation.

Measurements are made of manual control performance in the closed-loop task of nulling perceived self-rotation velocity about an earth-vertical axis. Self-velocity estimation is modeled as a function of the simultaneous presentation of vestibular and peripheral visual field motion cues. Based on measured low-frequency operator behavior in three visual field environments, a parallel channel linear model is proposed which has separate visual and vestibular pathways summing in a complementary manner. A dual-input describing function analysis supports the complementary model; vestibular cues dominate sensation at higher frequencies. The describing function model is extended by the proposal of a non-linear cue conflict model, in which cue weighting depends on the level of agreement between visual and vestibular cues.

Fourier Analysis↗
PubMed1981

Sensation of rotation about a vertical axis with a fixed visual field in different illuminations and in the dark.

This paper compares the motion sensations of a subject rotated about a vertical axis for two fixed visual fields (a large peripheral field and a single central spot) and in darkness. Motion sensation is described in terms of threshold, frequency response, and subjective displacement and velocity. The perception of angular acceleration showed significantly lower threshold and reduced latency time for the illuminated presentation. The level of illumination, however, produced no significant difference in threshold. The subjective frequency response, measured by a nulling method, showed a higher gain in the illuminated presentation, particularly at low frequencies and accelerations. With the subject rotating a pointer to maintain a fixed heading during triangular velocity stimuli, subjective displacements showed no difference for all different visual cues. Magnitude estimates of the after-rotation associated with deceleration from a constant velocity showed a quicker rising speed, larger subjective velocity and longer duration in the illuminated presentation. All the results suggest that the oculogyral illusion is principally responsible for producing a lower threshold in the illuminated presentation, although the fixed peripheral visual field tends to reduce reliance upon vestibular signals. At lower intensity rotation stimuli, this effect is especially apparent.

Adult↗
PubMed1981

Ocular torsion on earth and in weightlessness.

Ocular torsion (OT) was measured in human subjects during horizontal linear acceleration on a sled in the laboratory and when emerging from weightlessness during parabolic flights in NASA's KC-135 aircraft. Analysis of the frequency response of OT to sinusoidal horizontal oscillation on earth shows results consistent with constant tilt rate studies and with earlier models based on perception of acceleration. Step responses of OT to lateral acceleration are compared to similar profiles from aircraft tests with no preexisting gravitoinertial force on the otoliths. The sensitivity of OT to rotating wide fields producing vection and to tactile cues is compared for earth and weightlessness. A new instrument for high bandwidth video measurement of OT using a soft-contact-lens target is described.

Acceleration↗
PubMed1981

Frequency response of the vestibulo-ocular reflex (VOR) in the monkey.

The frequency response of the vestibulo-ocular reflex has been investigated in the alert monkey during sinusoidal rotation about a vertical axis ina frequency range of 0.001-0.5 Hz. Phase and gain of nystagmus slow phase velocity was determined. In the frequency range above 0.1 Hz, nystagmus slow phase velocity was in phase with (compensated for) head velocity. At lower frequencies, an increasing phase lead was present which could reach more than 90 degrees. Gain fell off correspondingly at low frequencies. Calculated time constants were 10-40 s in different monkeys. Animals which had been exposed to numerous previous rotary stimuli in the laboratory showed much shorter time constants than did "naive" monkeys.

Animals↗