PubMed Health⌕ Search

Biomedical subjects

K Money

Publications and source records attributed to K Money.

5 recordsLinked to original sources
PubMed1998

Oculomotor response to linear acceleration as induced by counter-rotation in supine subjects.

BACKGROUND: Horizontal nystagmus occurs in response to sinusoidal linear accelerations directed along an upright subject's Y (interaural) axis, and is proposed to be mediated by an utricular otolith mechanism. HYPOTHESIS: The otolith organs, composed of the utricles and saccules, provide a unique set of signals for any linear acceleration in 3-dimensional space. A supine subject under alternate changing directions of linear acceleration as induced by counter-rotation will receive alternate stimulation along the Y as well as the Z (dorsoventral) axis. We hypothesized that alternate horizontal and vertical nystagmus would be elicited as a result of the changing direction of linear acceleration. METHODS: A group of eight subjects in the supine position were exposed to counter-rotation at 0.16, 0.25, and 0.33 Hz. Vertical and horizontal eye movements were recorded simultaneously using the El-Mar eye and head tracking system. RESULTS: Horizontal nystagmus was observed in all supine subjects. The direction of the slow phase of nystagmus changed with directional changes in linear acceleration. Reversals in the direction of eye movements lagged behind the reversals in the direction of the acceleration. However, only two subjects exhibited alternating horizontal and vertical nystagmus as a result of changing axis of linear acceleration, from "along the Y axis" to "along the Z axis." CONCLUSION: We propose that the nystagmus induced in the supine subject was provoked by linear acceleration and largely an otolith-mediated reflex. The lack of vertical response could be due to the relative paucity of vestibular afferents information along the dorsoventral axis.

Acceleration↗
PubMed1995

Spatial disorientation-implicated accidents in Canadian forces, 1982-92.

In a recent survey of CF18 aircrew human factors, 44% of pilots reported experience with spatial disorientation (SD), of whom 10% had experienced more than 3 episodes. In order to investigate further, we have completed a retrospective study of SD-implicated category A accidents (where an aircraft is destroyed, declared missing, or damaged beyond economic repair) in the Canadian Forces (CF) during 1982-92. An overview of all SD occurrences (including accidents and incidents) across aircraft types is also presented. Information was gathered concerning the genesis and severity of disorientation so that research effort and pilot training could be appropriately implemented. Mishap investigation summaries involving category A accidents where SD was implicated were obtained from the CF Directorate of Flight Safety and reviewed. We also examined in detail the Board of Inquiry Reports of these accidents. The role of disorientation in these accidents was assessed. There were 62 category A accidents between 1982-92 and, in 14, SD had been assigned as a possible cause factor in the accident records. When divided into the categories of Recognized SD (RSD), Unrecognized SD (USD), and Incapacitating SD (ISD), all but two fell into the category of USD (the pilots were unaware of the disorientation). Of the SD accidents, 11 involved a total loss of 24 lives. The majority of the accidents happened during the day, and pilots' cumulative flying experience did not appear to be a significant factor. According to our assessment, there were two episodes of vestibular origin, involving the somatogravic illusion. Three episodes of disorientation occurred over frozen lakes, one over glassy water, and one over ocean.(ABSTRACT TRUNCATED AT 250 WORDS)

Accidents, Aviation↗
PubMed1992

Human ocular torsion during parabolic flights: an analysis with scleral search coil.

Rotation of the eyes about the visual axis is known as ocular torsion. A lateral inclination (a "roll") of the head induces ocular torsion in the opposite direction, a response known as ocular counterrolling. For six subjects, we recorded the static (head still) and dynamic (head in oscillatory roll motion) ocular torsion in normal 1 g condition and also during the microgravity and hypergravity periods of parabolic flight, using the electromagnetic scleral search coil technique. With the head still, the direction and magnitude of torsion that occurred in response to microgravity and hypergravity differed substantially from one individual to another, but there was a significant difference in torsional magnitude between the microgravity and hypergravity periods, for all static head positions including the upright position. Under normal 1 g conditions, counterrolling compensated for about 16% of (voluntary) static head roll, while dynamic counterroll was much larger, up to 36% of head roll at 0.55 Hz. With increasing frequency of head oscillation between 0.33 Hz and 0.55 Hz, the gain of counterrolling increased and there was no change in the phase relationship. The gain of dynamic counterroll (in response to voluntary head rolling) was not significantly less in hypogravity, suggesting that on the ground at these frequencies the contribution of gravity and gravity receptors to this reflex is redundant: this reflex is probably driven by the semicircular canals. In some subjects, the torsional displacement in microgravity is accompanied by micro-torsional oscillatory motion.

Adult↗
PubMedDate not supplied

Visual influence on head shaking using the vestibular autorotation test.

In this study we investigated the vestibular system by recording eye movements in response to voluntary high-frequency head-only movements using the Vestibular Autorotation Test (VAT; Western System Research Inc., Los Angeles, California). Our objective was to evaluate if the VAT could be implemented as one of the screening tests for vestibular integrity in aircrews and potential pilots. We attempted to record horizontal and vertical eye movements using electrooculography and head velocity with calibrated rotational velocity sensors. The gain and phase of the input and output signals were computed by discrete Fourier analysis. Seated subjects were instructed to fixate on a real or imaginary target while making smooth head oscillations about the spinal axis in time to an audible cue from 0.5 to 6.0 Hz/during an 18-second test period. Test trials included two conditions in the light with subjects fixated on a real target (C1) or on an imaginary target on a blank screen (C2); three conditions in the dark in which subjects fixated on an imaginary target (C3), fixated on a remembered LED target in the dark after it was extinguished (C4), or fixated on a real target (C5). All the dark trials were performed after dark adaptation for 30 minutes. We were not able to obtain consistent vertical VOR response (when the subjects oscillated their head about the interaural axis) using the VAT. For horizontal eye movements from 2.0 to just over 4.7 Hz, when subjects fixated on an imaginary target, there was an unexpected and significant increase in the gain of the eye movement velocities in the dark as compared to the gain obtained in the light conditions. In the dark trials, the gain was significantly higher when the subjects fixated on an imaginary target as opposed to a real target. There was no difference in phase among all conditions. This test could potentially serve for preliminary screening for the integrity of the vestibular system as it is noninvasive and of short duration. However, caution must be exercised in controlling various variables. Extensive normative data are needed to properly assess this test as a screening tool for aircrews.

Adult↗