On the mechanism of energy transfer to Tb3+ ions in proteins. A time-resolved luminescence study of the Tb-elastase complex.

Intraprotein energy transfer to terbium ions is widely used for probing distances of calcium sites in proteins. In this work we have performed a time-resolved study of the sensitized luminescence in elastase using a pulsed laser excitation at 265 nm. Terbium-sensitized luminescence was found to build-up within about 150 microseconds, which indicates that the protein transfers energy at a rate several orders of magnitude slower than expected for a singlet state donor. From the rise time of the signal and from its variation with the oxygen concentration, it can be deduced that 80% of the transfer originates from the first triplet excited state of one unique aromatic residue. From the comparison of protein fluorescence and sensitized terbium luminescence excitation spectra the sensitizer was identified as a tryptophan, presumably Trp141, which is situated only 0.7-0.9 nm away from the Tb site. The results are at variance with the usual assumption that energy is transferred from the first excited singlet state of aromatic residues according to a long-range dipole-dipole interaction and are more consistent with a short-distance exchange mechanism.

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.

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.

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.

Motion sickness susceptibility: a retrospective comparison of laboratory tests.

A test battery designed primarily to assess vestibular function has been used for several years to evaluate individuals referred to our laboratory. Because some of the test conditions have proved to be nauseogenic to some individuals, methods of assessing disturbance during these procedures have been used to pursue a second goal, viz., the estimation of motion sickness susceptibility. This report, which focuses on the latter goal, is a retrospective comparison of results on three tests obtained from two groups of subjects, one of which was a group of Navy and Marine aviation personnel who had suffered multiple attacks of airsickness. Results from three laboratory tests of motion sickness susceptibility indicated that there are substantial differences between the airsick group and the unselected comparison group on observer ratings and individual self-ratings of motion sickness symptoms. The provocative stimuli in each laboratory test, as well as suggestions concerning how multiple tests may prove effective in predicting motion sickness, are discussed.

Some psychological correlates of motion sickness susceptibility.

Four groups of 37 subjects each (highly susceptible men, highly susceptible women, nonsusceptible men, and nonsusceptible women) were obtained from a population of 2,432 college students ranging in age from 18 to 39 years. Susceptibility to motion sickness was determined by scores on a motion sickness questionnaire (MSQ); only individuals with extreme scores were considered for inclusion in the experimental groups. The following tests were administered: Floor Ataxia Test Battery, State-Trait Anxiety Inventory, Menstrual Distress Questionnaire, Cornell Medical Index, Cornell Work Form, Eysenck Personality Inventory, Rotter Internal-External Locus of Control Scale, and the 16 Personality Factors test. Each subject was tested on at least three, but not more than six, of the eight tests. Significant sex differences were obtained on the ataxia battery and the Cornell Medical Index. Susceptible subjects did not differ significantly from nonsusceptibles on the ataxia battery but did differ significantly on all personality tests except the Menstrual Distress Questionnaire (administered only to women) and the Rotter Scale. The generally consistent and significant patterns of results from the psychological tests probably reflect the selection factors used in defining the subject groups; certain personality characteristics are associated with a high degree of susceptibility to motion sickness.

Motion sickness susceptibility and related behavioral characteristics in men and women.

The incidence of motion sickness in a large (N = 3,618) college population was determined by means of a questionnaire. The test-retest reliability coefficient (0.84) suggested that the motion sickness questionnaire (MSQ) for this particular population yields highly consistent information. Significantly greater proportions of men than women had low susceptibility scores and, conversely, significantly greater proportions of women had high susceptibility scores. The relationships between motion sickness susceptibility scores and several behavioral characteristics in men and women were also investigated. Specifically, comparisons of MSQ scores were made with other self-assessments, age changes, motion experiences, familial susceptibility, use of motion sickness medication, muscular coordination, willingness to participate in motion experiments, flying experience, phobias, visual motion effects, and use of alcohol.

Nystagmus, turning sensations, and illusory movement in motion sickness susceptibility.

The relationships of motion sickness susceptibility to nystagmic eye movements, sensations of turning, and duration of the spiral aftereffect were determined with 48 subjects separated into groups on the basis of sex and extremes of motion sickness susceptibility. When subjective alertness levels were controlled, there was no enhancement of elicited nystagmus nor turning sensations in susceptible individuals. However, spiral aftereffect durations were significantly longer in susceptible individuals than in nonsusceptible individuals. The results are interpreted as favoring Graybiel's model of the structural elements in motion sickness.