Simulated flight path control of fighter pilots and novice subjects at +3 Gz in a human centrifuge.

BACKGROUND: We have previously shown that subjects produce exaggerated manual forces in +3 Gz. When subjects execute discrete flight path changes in a flight simulator, their performance is less stable in +3 Gz than in +1 Gz. Here we explore whether Gz-related deficits are found with continuous flight path changes. METHODS: Novice subjects and fighter pilots sat in a high-fidelity flight simulator equipped with the reproduction of the Eurofighter 2000 cockpit, including the realistic flight stick, and pursued continuous altitude changes of a target airplane in +1 Gz and +3 Gz. Subjects also produced verbal responses in a Stroop task. Pursuit and Stroop tasks were administered alone and concurrently. RESULTS: Flight instability increased in +3 Gz compared to +1 Gz in novices (+46%), but not in pilots (+3%), and even there only during the first minute. Flight performance improved after the first minute in both subject groups. Stroop reaction time was higher in novices (+5.27%) than in pilots (+3.77%) at +3 Gz. Dual-task costs did not differ between groups or Gz levels. DISCUSSION: Deficits of force production in high Gz are largely compensated for when subjects apply forces to produce a continuously changing flight path. This compensation seems not to require additional cognitive resources and may be achieved by using visual feedback. Force production deficits in high Gz seem to have no appreciable effects on flight performance and cognitive load of experienced pilots using a force-plus-displacement stick in +3 Gz. It remains to be shown whether this conclusion extends to purely isometric sticks and to higher Gz levels.

Stability of simulated flight path control at +3 Gz in a human centrifuge.

INTRODUCTION: Earlier studies have shown that naïve subjects and experienced jet pilots produce exaggerated manual forces when exposed to increased acceleration (+Gz). This study was designed to evaluate whether this exaggeration affects the stability of simulated flight path control. METHODS: We evaluated naïve subjects' performance in a flight simulator which either remained stationary (+1 Gz), or rotated to induce an acceleration in accordance to the simulated flight path with a mean acceleration of about +3 Gz. In either case, subjects were requested to produce a series of altitude changes in pursuit of a visual target airplane. Resulting flight paths were analyzed to determine the largest oscillation after an altitude change (Oscillation) and the mean deviation between subject and target flight path (Tracking Error). RESULTS: Flight stability after an altitude change was degraded in +3 Gz compared to +1 Gz, as evidenced by larger Oscillations (+11%) and increased Tracking Errors (+80%). These deficits correlated significantly with subjects' +3 Gz deficits in a manual-force production task. DISCUSSION: We conclude that force exaggeration in +3 Gz may impair flight stability during simulated jet maneuvers in naïve subjects, most likely as a consequence of vestibular stimulation.

Visual field motion effects on the production of manual forces and displacements.

BACKGROUND: We have previously shown that subjects produce exaggerated arm forces when exposed to three times the normal gravitational acceleration (+3 Gz), and that this deficit is not related to direct mechanical effects, faulty proprioception, or increased cognitive load. Here we investigate whether it is related to vestibular activity. METHODS: Novice subjects observed a stationary, upward or downward moving visual field while producing pretrained arm forces (Exp. A, N = 12) or displacements (Exp. B, N = 12); a control group produced no motor responses and their arm EMG was registered (Exp. C, N = 12). RESULTS: Produced forces and EMG were higher with the moving than with the stationary field, irrespective of field direction (initial force +42%; peak force +20%, biceps brachii EMG +21%). Produced displacements were comparable with the moving and stationary field. DISCUSSION: The present pattern of findings is similar to that yielded previously in +3 Gz, which supports the existence of a common underlying mechanism. Specifically, we suggest that +3 Gz and vertical field motion stimulate the vestibular system, and that the observed exaggeration of produced force is due to vestibular modulation of descending volitional motor commands. The fact that displacements were not affected by +3 Gz and moving visual fields would then indicate that forces and displacements are controlled through distinct pathways which interact differently with the vestibular system.

Artificial gravity results in changes in frontal lobe activity measured by EEG tomography.

Mental and perceptual motor performance has been reported to be impaired during hypergravity. Current research has focused on physiological explanations (e.g., deficient proprioceptive feedback) and neglected psycho-physiological effects (e.g., arousal, emotion, cognitive engagement). This study aims at localising changes in brain cortical activity by using a distributed source localisation algorithm (sLORETA) to model the probable neural generators of changes in scalp voltage under hypergravity conditions. Brain cortical activity was measured by EEG before, during and after exposure to three time terrestrial gravity (3G(z)) on ten naive subjects aged 29+/-5 years. Changes in EEG activity were localised using standardised low resolution brain electromagnetic tomography (sLORETA) for alpha-1 [7.5-10 Hz], alpha-2 [10-12.5 Hz], beta-1 [12.5-18 Hz], beta-2 [18-35 Hz] and gamma [35-45 Hz] activities. Individual concentrations of blood cortisol and perceived psychological strain were related to changes in cortical current density. An increase in alpha-1 activity occurred in the right inferior frontal lobe, beta-1 activity was found to be increased in the limbic lobe during 3G(z). Post acceleration alpha-2 and beta-1 activities declined in frontal, temporal and limbic lobes. Changes in blood cortisol concentrations and perceived strain showed a clear relationship to changes in right sided frontal alpha-1 activity. We conclude that frontal activity during hypergravity may serve as a marker of anxiety. This puts a new light on the debate as to whether cognitive and sensorimotor impairments are attributable to primary physiological effects or secondary psychological effects of a hypergravity environment.

The effect of parabolic flight on perceived physical, motivational and psychological state in men and women: correlation with neuroendocrine stress parameters and electrocortical activity.

Previous findings of decreased mental and perceptual motor performance during parabolic flights have been attributed mainly to the primary effects of weightlessness rather than the accompanying effects of stress and altered mood. Although recent studies have alluded to the possible negative effects of stress on performance, there has been no attempt to investigate this during parabolic flights. Over a period of 3 years, 27 human participants (male n = 18, mean age +/- SD 34.67 +/- 7.59 years; female n = 9, 36.22 +/- 9.92 years) were recruited with the aim to evaluate if, and to what extent, parabolic flights are accompanied by changes in mood. Furthermore, the relationships between mood and physiological markers of stress and arousal, namely circulating stress hormones (ACTH, cortisol, epinephrine, norepinephrine, prolactin and brain activity (EEG)) were investigated. A strong and significant correlation was found between circulating stress hormone concentrations and perceived physical state, motivational state (MOT) and psychological strain (PSYCHO), whereas no interaction between mood and EEG or EEG and stress hormone concentrations was observed. Therefore, two different stress responses appear to be present during parabolic flight. The first seems to be characterised by general cortical arousal, whereas the second seems to evolve from the adrenomedullary system. It is likely that both these mechanisms have different effects on mental and perceptual motor performance, which require further investigation and should to be taken into account when interpreting previous weightlessness research.

Centrifugal acceleration to 3Gz is related to increased release of stress hormones and decreased mood in men and women.

It has been suggested that the central and peripheral neural processes (CPNP) are affected by gravitational changes. Based on the previous experiments during parabolic flights, central and peripheral changes may not only be due to the changed gravitational forces but also due to neuroendocrine reactions related to the psycho-physiological consequences of gravitational changes. The present study focuses on the interaction of neuroendocrine changes and the physical and mental states after acceleration to three-time terrestrial gravity (3Gz). Eleven participants (29.4+/-5.1 [SD] years (male (n=8): 30+/-5.1 years; female (n=3): 27.7+/-2.1 years) underwent a 15 min acceleration to 3Gz in a human centrifuge. Before and after the acceleration to 3Gz circulating stress hormone concentrations (cortisol, adrenocorticotropic hormone (ACTH), prolactin, epinephrine, norepinephrine) and perceived physical and mental states were recorded. A second control group of 11 participants underwent the same testing procedure in a laboratory session. Serum cortisol concentration during exposure to the centrifugal acceleration increased by 70%, plasma concentration of ACTH increased threefold, prolactin twofold, epinephrine by 70% and norepinephrine by 45%, whereas the perceived physical well-being decreased. These findings demonstrate that psycho-physiological changes have to be regarded as a relevant factor for the changes in CPNP during phases of hypergravity exposure.

Motor performance and motor learning in sustained +3 Gz acceleration.

INTRODUCTION: Previous studies have shown that increased head-to-foot acceleration (+Gz) like that experienced in maneuvering aircraft impairs motor performance. However, there are few studies of motor performance providing detailed descriptions of specific deficits (e.g., mechanical function, timing, or loss of accuracy), and almost none investigating motor learning processes. Therefore, the present study evaluated whether these parameters may explain tracking deficits during +Gz, and whether +Gz also affects motor learning. METHODS: To investigate motor performance, a Test Group (N = 10) manually tracked a sinusoidal moving target either in normal Earth gravity or during steady-state acceleration (+3 Gz). Cursor feedback was then left-right reversed, and subjects had to adapt their performance to this disturbance while remaining in the same acceleration environment. A Control Group (N = 10) performed the same paradigm in 1 G; a Weight Group (N = 12) also remained at 1 G with additional arm weighting to simulate the +3-Gz load. RESULTS: Tracking performance in +3 Gz was impaired by about 50% compared to 1-G values. The deficit was not entirely due to the mechanical effect of +3 Gz, since performance in the Weight Group decreased by only about 25%. Moreover, tracking accuracy but not tracking timing was impaired at +3 Gz. Left-right switching resulted in typical motor learning in all subjects. Exposure to +3 Gz had no influence on motor learning. DISCUSSION: Deficits in tracking performance are probably not due to mechanical impairment or timing deficits, but rather reflect effects on accuracy due to vestibulo-spinal influences or the stressful environment at +3 Gz However, these effects do not impair motor learning.

Isometric force production in experienced fighter pilots during +3 Gz centrifuge acceleration.

INTRODUCTION: Previously, we have shown that naïve subjects produce exaggerated isometric forces when exposed to increased acceleration (+Gz) for the first time. The present study investigates whether +G,-experienced PA-200 Tornado pilots show similar deficits. METHODS: Experiments were conducted in the stationary (+1 Gz) or rotating (+3 Gz) gondola of a human-rated centrifuge. With their dominant hand, seven pilots produced visually prescribed forces of specific direction and magnitude using an isometric joystick. In practice trials, subjects received continuous visual feedback about their performance, while in test trials they did not. RESULTS: Peak forces during test trials were significantly higher in +3 Gz than in +1 Gz, although this increase of about 25% referring to the +1 Gz value was somewhat smaller in pilots than in nonpilot controls (increase of about 36%). DISCUSSION: Since pilots' responses were exaggerated in +3 Gz, it seems that frequent exposure to varying +Gz levels is not sufficient for a profound adaptation of force-producing mechanisms to +3 Gz. In consequence, pilots' performance on isometric tasks could be compromised during flight maneuvers in +Gz.

Acceleration effects on manual performance with isometric and displacement joysticks.

BACKGROUND: We have shown before that novice human subjects produce exaggerated isometric forces when exposed to three times normal terrestrial acceleration (+3 Gz), and that this deficit is compensated by intensive training in +3 Gz. We now investigate whether training in normal terrestrial gravity (normal G) is also effective. We further examine whether subjects in +3 Gz produce not only exaggerated forces, but also exaggerated hand displacements. METHODS: Experiments were conducted in the stationary (normal G) or rotating (+3 Gz) gondola of a man-rated centrifuge. With their dominant hand, subjects produced either forces using an isometric joystick, or hand displacements using a regular joystick. Response directions and magnitudes were prescribed visually. In practice trials, subjects received continuous visual feedback about their performance, while in test trials they did not. RESULTS: Subjects produced exaggerated forces in +3 Gz, whether or not they previously practiced the task in normal G. In contrast, subjects did not produce exaggerated hand displacements in +3 Gz. DISCUSSION: Exaggerated force production in +3 Gz is not overcome by task practice in normal G, as opposed to task practice in +3 Gz. This might be an indication that pilot training should contain extended practice of force production during phases of increased gravity (+Gz) to avoid motor deficits during flight maneuvers inducing +Gz. Furthermore, the control of isometric and regular joysticks seems to be based on partly distinct neural mechanisms, with different +Gz dependence. Thus, against the background of motor performance during +Gz, regular sticks might be favorably compared to isometric sticks in high-performance aircrafts.