Simulator-induced spatial disorientation: effects of age, sleep deprivation, and type of conflict

INTRODUCTION: Spatial disorientation mishaps are greater at night and with greater time on task, and sleep deprivation is known to decrease cognitive and overall flight performance. However, the ability to perceive and to be influenced by physiologically appropriate simulated SD conflicts has not previously been studied in an automated simulator flight profile. METHODS: A set of 10 flight profiles were flown by 10 U.S. Air Force (USAF) pilots over a period of 28 h in a specially designed flight simulator for spatial disorientation research and training. Of the 10 flights, 4 had a total of 7 spatial disorientation (SD) conflicts inserted into each of them, 5 simulating motion illusions and 2 involving visual illusions. The percentage of conflict reports was measured along with the effects of four conflicts on flight performance. RESULTS: The results showed that, with one exception, all motion conflicts were reported over 60% of the time, whereas the two visual illusions were reported on average only 25% of the time, although they both significantly affected flight performance. Pilots older than 35 yr of age were more likely to report conflicts than were those under 30 yr of age (63% vs. 38%), whereas fatigue had little effect overall on either recognized or unrecognized SD. DISCUSSION: The overall effects of these conflicts on perception and performance were generally not altered by sleep deprivation, despite clear indications of fatigue in our pilots.     

Modafinil's effects on simulator performance and mood in pilots during 37 h without sleep

INTRODUCTION: Modafinil is a relatively new alertness-enhancing compound of interest to the military aviation community. Although modafinil has been well-tested in clinical settings, additional studies are required to establish its safety and efficacy for use in pilots. OBJECTIVE: The purpose of this study was to determine whether modafinil (100 mg after 17, 22, and 27 h without sleep) would attenuate the effects of fatigue on fighter-pilot mood and performance during 37 h of continuous wakefulness. METHODS: A quasi-experimental, single-blind, counterbalanced design tested the effects of modafinil in 10 Air Force F-117 pilots. RESULTS: Modafinil attenuated flight performance decrements on six of eight simulator maneuvers. Overall, modafinil maintained flight accuracy within approximately 15-30% of baseline levels, whereas performance under the no-treatment/placebo condition declined by as much as 60-100%. Modafinil decreased self-ratings of depression and anger, while improving ratings of vigor, alertness, and confidence. Benefits were most noticeable after 24 to 32 h of continuous wakefulness. One potential drawback of modafinil was that, at least at the 100-mg dose level, the drug's effects were not subjectively salient. Since this may lead personnel to escalate the dose without flight surgeon approval, personnel should be cautioned regarding this particular drug characteristic. CONCLUSION: Although modafinil did not sustain performance at predeprivation levels, the present study suggests that modafinil should be considered for the military's armament of short-term fatigue countermeasures. Future research will evaluate whether 200-mg doses are more beneficial than the 100-mg doses used here.     

Heart rate and performance during combat missions in a flight simulator

INTRODUCTION: The psychological workload of flying has been shown to increase heart rate (HR) during flight simulator operation. The association between HR changes and flight performance remains unclear. METHODS: There were 15 pilots who performed a combat flight mission in a Weapons Tactics Trainer simulator of an F-18 Hornet. An electrocardiogram (ECG) was recorded, and individual incremental heart rates (deltaHR) from the HR during rest were calculated for each flight phase and used in statistical analyses. The combat flight period was divided into 13 phases, which were evaluated on a scale of 1 to 5 by the flight instructor. RESULTS: HR increased during interceptions (from a mean resting level of 79.0 to mean value of 96.7 bpm in one of the interception flight phases) and decreased during the return to base and slightly increased during the ILS approach and landing. DeltaHR appeared to be similar among experienced and less experienced pilots. DeltaHR responses during the flight phases did not correlate with simulator flight performance scores. Overall simulator flight performance correlated statistically significantly (r = 0.50) with the F-18 Hornet flight experience. CONCLUSIONS: HR reflected the amount of cognitive load during the simulated flight. Hence, HR analysis can be used in the evaluation of the psychological workload of military simulator flight phases. However, more detailed flight performance evaluation methods are needed for this kind of complex flight simulation to replace the traditional but rough interval scales. Use of a visual analog scale by the flight instructors is suggested for simulator flight performance evaluation.     

模拟飞行条件下双重任务时飞行员心理生理参数的变化特点

测量了50名健康飞行员和13名康复疗养飞行员，在模拟飞行条件下双重任务时的心理生理反应。结果发现，模拟飞行各阶段心率变化趋势与实际飞行基本一致，但变化幅度较低。双重任务时，反映情绪性变化的心率、呼吸率及肺通气量明显增加，与思维活动有关的眨眼率增加。心理运动反应速度与飞行操纵质量相互影响，其程度有个体差异。同时在该负荷环境下，发现5例心律失常的无症状飞行员。结果提示，模拟飞行双重任务条件可以造成飞行员心理生理负荷，并可能有助于发现一些潜在性病症。     

Rotation rate and duration effects on the somatogyral illusion

INTRODUCTION: Aviation spatial disorientation mishaps remain a concern, especially due to their fatality rate. Some of the most insidious disorientations are due to vestibular stimuli in the absence of visual cues. A category of such disorientations are known as somatogyral illusions. METHODS: To determine the effects of spin rate and duration on the perception of the somatogyral illusion, we examined the subjective response of pilots and non-pilots to rotation around the yaw axis in a flight simulator in a manner that would mimic two vestibular illusions found in flight: the washout of the semi-circular canals following sustained turns, and the illusory counter-rotation following return to straight and level flight. There were 29 subjects (14 pilots) who were seated blindfolded in a flight simulator which accelerated to constant plateau rotation rates of 20, 70, and 120 degrees x s(-1) and then decelerated to stationary; plateaus were 10, 20, or 40 s. Subjects reported 1) the time when the perception of rotation ceased (i.e., the subjective time until washout was reached); 2) the relative magnitude of the counter-rotation experienced; and 3) the time until the perception of counter-rotation ceased. Subjects also manipulated a slider to provide a continuous subjective measure of their experience of rotation. RESULTS: The two time measures increased with increases in both the duration and magnitude of the spin. The increase in perceived washout time with spin rate was non-linear (geometric). There was an interaction between spin duration and spin rate on the experience of illusory counter-rotation magnitude such that at low rates, spin duration had no effect, but its effect increased at faster rates. The time constant of adaptation of the semicircular canals was estimated to be 8.3 s. DISCUSSION: The effects were validated against a model of semicircular canal and cupola adaptation, which predicted the data with high accuracy. Pilots and non-pilots did not differ in their illusory experience.     

Simulator induced syndrome: evidence for long-term aftereffects

Pilots have experienced various adverse symptoms hours and even days following flight simulator training. This study surveyed pilots undergoing simulator training in an attempt to provide an initial gauge of the extent, severity, and possible risk factors of long-term (greater than 1 day) simulator aftereffects. A three-part voluntary and anonymous questionnaire was used to gather data. We studied pilots of varying experience undergoing advanced flight training which included the use of flight simulators. Some 238 pilots participated in the study, and 196 completed the follow-up survey concerning long-term effects. Nine (4.6%) pilots experienced adverse symptoms 24 h or more after completion of their last simulator training, which they attributed to their recent simulator experience. Symptoms reported included: recurrent visual flashbacks, continued balance disturbance, and hand-eye discoordination. Three pilots (1.5%) reported difficulties flying aircraft. Pilot flight experience level, total simulator time, length of simulator session, and sex were not predictive of risk. This study suggests that long-term (greater than 1 day) adverse aftereffects may occur following simulator training.     

Visual and flight performance recovery after PRK or LASIK in helicopter pilots

INTRODUCTION: Refractive surgery, specifically photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK), is becoming more accepted in the military environment. Determination of the impact on visual performance in the more demanding aviation environment was the impetus for this study. METHODS: A prospective evaluation of 20 Black Hawk pilots pre-surgically and at 1 wk, 1 mo, and 6 mo postsurgery was conducted to assess both PRK and LASIK visual and flight performance outcomes on the return of aviators to duty. RESULTS: Of 20 pilots, 19 returned to flight status at 1 mo after surgery; 1 PRK subject was delayed due to corneal haze and subjective visual symptoms. Improvements were seen under simulator night and night vision goggle flight after LASIK; no significant changes in flight performance were measured in the aircraft. Results indicated a significantly faster recovery of all visual performance outcomes 1 wk after LASIK vs. PRK, with no difference between procedures at 1 and 6 mo. Low contrast acuity and contrast sensitivity only weakly correlated to flight performance in the early post-operative period. DISCUSSION: Overall flight performance assessed in this study after PRK and LASIK was stable or improved from baseline, indicating a resilience of performance despite measured decrements in visual performance, especially in PRK. More visually demanding flight tasks may be impacted by subtle changes in visual performance. Contrast tests are more sensitive to the effects of refractive surgical intervention and may prove to be a better indicator of visual recovery for return to flight status.     

Effect of caffeine on simulator flight performance in sleep-deprived military pilot students

Caffeine has been suggested to act as a countermeasure against fatigue in military operations. In this randomized, double-blind, placebo-controlled study, the effect of caffeine on simulator flight performance was examined in 13 military pilots during 37 hours of sleep deprivation. Each subject performed a flight mission in simulator four times. The subjects received either a placebo (six subjects) or 200 mg of caffeine (seven subjects) 1 hour before the simulated flights. A moderate 200 mg intake of caffeine was associated with higher axillary temperatures, but it did not affect subjectively assessed sleepiness. Flight performance was similar in both groups during the four rounds flown under sleep deprivation. However, subjective evaluation of overall flight performance in the caffeine group tended to be too optimistic, indicating a potential flight safety problem. Based on our results, we do not recommend using caffeine pills in military flight operations.     

Contrast sensitivity: establishing normative data for use in screening prospective naval pilots

BACKGROUND: Contrast sensitivity testing can be a useful supplement to standard visual acuity tests. Currently there are no standards for contrast sensitivity in military aviation. Student naval pilots, who often have better-than-average visual acuity, could be expected to have better-than-average contrast sensitivity. Any attempt to establish contrast sensitivity standards for military aviation should begin with establishing normative data, particularly data gathered from the military aviation community. HYPOTHESIS: Student naval pilots differ from the general military population on Small Letter Contrast Test measurements. METHODS: Contrast sensitivity was measured in a group of student naval pilots (n = 107) and compared with results from aviation and non-aviation personnel. The Small Letter Contrast Test (SLCT) was used (19). Other subjects consisted of student naval flight officers (n = 40), experienced naval pilots and flight officers (n = 35 and 86, respectively), enlisted aircrew (n = 175), and other military personnel tested before undergoing photorefractive keratectomy (n = 185). RESULTS: Data collected provide large-group demographic characteristics and normative values for contrast sensitivity measured with the SLCT. Of the non-aviation controls, 95% scored at least 0.62 (read at least 7 lines plus 2 of 10 letters on the 8th line of the chart), and 95% of the student pilots scored at least 0.81, (read at least 9 lines plus 1 letter on the 10th line). CONCLUSION: Student naval pilots scored significantly better on the SLCT than the military control population. The SLCT shows potential as a screening device during induction physical examinations of military pilots.     

Cervical spine degeneration in fighter pilots and controls: a 5-yr follow-up study

At 5 yr after MRI of the cervical spine, for evaluation concerning degenerative lesions, follow-up MRI was performed on asymptomatic experienced military high performance aircraft pilots (mean age 47 yr; mean accumulated flying time 3,100 h) and on age-matched controls without military flying experience. Young military high performance aircraft pilots (mean age 28 yr, mean accumulated flying time 915 h) were also re-examined. Compared with baseline MRI 5 yr earlier, there was significant increase in disk protrusions in all groups, in osteophytes in controls, and in foraminal stenoses in experienced pilots, and a significant reduction in disk signal intensity in young pilots. The difference between experienced pilots and controls was markedly reduced compared with that at baseline MRI. Thus, military high performance aircraft pilots seem to be at increased risk of premature development of degenerative lesions of the same type as are seen in an aging population. With increasing age the difference between pilots and controls diminishes.     

The effects of visual scenes on roll and pitch thresholds in pilots versus nonpilots

BACKGROUND: Previous studies have indicated that, compared with nonpilots, pilots rely more on vision than "seat-of-the-pants" sensations when presented with visual-vestibular conflict. The objective of this study was to evaluate whether pilots and nonpilots differ in their thresholds for tilt perception while viewing visual scenes depicting simulated flight. METHODS: This study was conducted in the Advanced Spatial Disorientation Demonstrator (ASDD) at Brooks AFB, TX. There were 14 subjects (7 pilots and 7 nonpilots) who recorded tilt detection thresholds in pitch and roll while exposed to sub-threshold movement in each axis. During each test run, subjects were presented with computer-generated visual scenes depicting accelerating forward flight by day or night, and a blank (control) condition. RESULTS: The only significant effect detected by an analysis of variance (ANOVA) was that all subjects were more sensitive to tilt in roll than in pitch [F (2,24) = 18.96, p < 0.001]. Overall, pilots had marginally higher tilt detection thresholds compared with nonpilots (p = 0.055), but the type of visual scene had no significant effect on thresholds. CONCLUSION: In this study, pilots did not demonstrate greater visual dominance over vestibular and proprioceptive cues than nonpilots, but appeared to have higher pitch and roll thresholds overall. The finding of significantly lower detection thresholds in the roll axis vs. the pitch axis was an incidental finding for both subject groups.     

Heat stress reduction of helicopter crew wearing a ventilated vest

BACKGROUND: Helicopter pilots are often exposed to periods of high heat strain, especially when wearing survival suits. Therefore, a prototype of a ventilated vest was evaluated on its capability to reduce the heat strain of helicopter pilots during a 2-h simulated flight. HYPOTHESIS: It was hypothesized that the ventilated vest would reduce pilot heat stress. METHODS: Five male and one female helicopter pilots flew for 2 h in a simulator in three different conditions; 15 degrees C wet bulb globe temperature (WBGT) without ventilation, 32 degrees C WBGT without ventilation, and 32 degrees C WBGT with a ventilated vest. RESULTS: Wearing the ventilated vest significantly reduced the increase in rectal temperature and increased thermal comfort. This made it possible for all subjects to complete the 2-h session. CONCLUSION: With the ventilated vest the subjects experienced less heat stress, thereby allowing all subjects to successfully complete the experiment, though two of the six pilots could not complete the 2-h flying task in the hot condition without cooling due to heat-related problems.     

The effect of repeated doses of 30 mg pyridostigmine bromide on pilot performance in an A-4 flight simulator

The effect of repeated doses of 30 mg pyridostigmine bromide every 8 h on flight skills in an A-4 simulator was tested in this crossover double-blind placebo-controlled study on 10 pilots experienced in actual and simulated A-4 flights. The pilots flew two test simulator flights 2 h after the fourth dose of pyridostigmine or placebo. The flight profile included navigation, rapid ascent, 360 degrees turns, and instrument landing. Each flight lasted approximately 20 min. Flight parameters measured included indicated air speed, true heading, barometric altitude, vertical velocity, and bank. The mean whole blood cholinesterase inhibition level was 29%. There was no decrement in performance under treatment with pyridostigmine in the percent of deviation time from the prescribed limits or in the average duration or magnitude of the deviation in each of the flight parameters. We conclude that pyridostigmine bromide in repeated doses of 30 mg every 8 h does not appear to influence pilot performance during short A-4 missions.     

Simulator sickness in the U.S. Army UH-60A Blackhawk flight simulator.

Realistic training in aviation now includes the use of sophisticated flight simulators which can provide near total perception of aircraft flight. Reports of simulator sickness seem to be increasing in simulators with multi-directional motion, computer-generated imagery, and infinity optics. A voluntary, subjective, symptom-oriented questionnaire was completed by 141 pilots after training in the UH-60A 2B38 Blackhawk flight simulator. Thirty-six percent reported positive symptoms of motion sickness. Pilots may be at risk if they fly too soon after simulator training and a mandatory grounding time is advised.     

EEG and ECG changes during simulator operation reflect mental workload and vigilance

BACKGROUND: Performing mission tasks in a simulator influences many neurophysiological measures. Quantitative assessments of electroencephalography (EEG) and electrocardiography (ECG) have made it possible to develop indicators of mental workload and to estimate relative physiological responses to cognitive requirements. OBJECTIVE: To evaluate the effects of mental workload without actual physical risk, we studied the cortical and cardiovascular changes that occurred during simulated flight. METHODS: There were 12 pilots (8 novices and 4 experts) who simulated a flight composed of 10 sequences that induced several different mental workload levels. EEG was recorded at 12 electrode sites during rest and flight sequences; ECG activity was also recorded. Subjective tests were used to evaluate anxiety and vigilance levels. RESULTS: Theta band activity was lower during the two simulated flight rest sequences than during visual and instrument flight sequences at central, parietal, and occipital sites (p < 0.05). On the other hand, rest sequences resulted in higher beta (at the C4 site; p < 0.05) and gamma (at the central, parietal, and occipital sites; p < 0.05) power than active segments. The mean heart rate (HR) was not significantly different during any simulated flight sequence, but HR was lower for expert subjects than for novices. The subjective tests revealed no significant anxiety and high values for vigilance levels before and during flight. CONCLUSIONS: The different flight sequences performed on the simulator resulted in electrophysiological changes that expressed variations in mental workload. These results corroborate those found during study of real flights, particularly during sequences requiring the heaviest mental workload.     

模拟长航时飞行心理疲劳的对抗措施效果评价

目的评价模拟长航时飞行时心理疲劳的对抗措施的效果。方法16名男性飞行学员按抽签法随机分为对照组和试验组,在教-8飞行模拟器上进行8h的航线飞行。试验组施加心理疲劳对抗措施。通过模拟电码判译成绩、飞行成绩和焦虑自评量表（self-r ating anxiety scale,SAS）评分评价对比两组飞行学员的心理疲劳程度。结果随着飞行时间的增加,对照组的电码判译成绩、飞行成绩均显著下降（F=4．406、10．166,P=0．039、0．002）,试验组的两项成绩则均无显著下降（F=1．015、0．780,P=0．405、0．477）;对照组在飞行4h后,两项成绩与试验开始阶段相比差异有统计学意义（P〈0．05）,试验组的成绩则在飞行开始后的各时段间差异均无统计学意义（P〉0．05）。飞行前后,对照组的SAS得分无明显变化（t=1．032,P=0．329）;飞行后试验组的SAS得分则出现显著降低,与飞行前比较差异有统计学意义（t=3．222,P=0．010）。结论本研究采用的心理疲劳对抗措施对长航时飞行引起的心理疲劳现象有明显的对抗效果。     

Monocular peripheral vision as a factor in flight safety

The performance of static visual identification tasks and simulated operational flying tasks, by nine binocular pilots and nine adapted monocular pilots, was measured in a unique operational visual simulator. It was hypothesized that, with head free to move, and adapted monocular pilot would perform as well as a binocular pilot, while an unadapted monocular (simulated by covering an eye) would perform less well. Other hypotheses were advanced. The static primary central task required sequential identification of dial readings. The dynamic primary central task involved simulated aircraft landing operations. During each set of primary tasks, a set of secondary peripheral visual tasks was performed. Results of the primary tasks and times of execution of the secondary tasks were subjected to analysis of variance. Factors included head position (fixed or free), stimulus location in peripheral field, eye state (seeing eye, blind eye), and type of central task (static, dynamic). All hypotheses were validated.     

MRI cervical spine findings in asymptomatic fighter pilots

MRI of the cervical spine for evaluation concerning degenerative lesions was performed on asymptomatic experienced military high performance aircraft pilots (mean age 42 yr with mean accumulated flying time of 2600 h), and for comparison on age-matched controls without military flying experience. Young military high performance aircraft pilots (mean age 23 yr with 220 h of flying per person) were also examined. There were significantly more osteophytes, disk protrusions, compressions of the spinal cord and foraminal stenoses in the experienced pilots than in the age-matched controls. Low frequency of low grade degenerative lesions was found in the young and inexperienced pilots.     

The effects of acoustic orientation cues on instrument flight performance in a flight simulator

An initial version of an acoustic orientation instrument (AOI), in which airspeed was displayed as sound frequency, vertical velocity as amplitude modulation rate, and bank angle as right-left lateralization, was evaluated in a T-40 (Link GAT-3) motion-based simulator. In this study, 15 pilots and 3 non-pilots were taught to use the AOI and flew simulated flight profiles under conditions of neither visual nor auditory instrumentation (NO INPUT), AOI signals only (AOI), T-40 simulator instrumentation only (VISUAL), and T-40 simulator instrumentation with AOI signals (BOTH). Bank control under AOI conditions was significantly better than under the NO INPUT condition for all flying tasks. Bank control under VISUAL conditions was significantly better than under the AOI condition only during turning and when performing certain complex secondary tasks. The pilots' ability to use the AOI to control vertical velocity and airspeed was less apparent. However, during straight-and-level flight, turns, and descents the AOI provided the pilots with sufficient information to maintain controlled flight. Factors of potential importance in using sound to convey aircraft attitude and motion information are discussed.     

The measurement of visual efficiency standards for pilots in the United States Air Force

Military aviation requires a high degree of visual skill and efficiency. The current visual standards for flying status in the United States Air Force employ static tests of visual function. Visual factors utilized in flight are continually changing to meet the demands of the situation. This study evaluates the performance of two carefully matched samples of people on a test of dynamic visual change, i.e., vergence facility. We compared the ability of a sample of military pilots to make rapid fusional movements in a base-in and base-out direction with a group of nonpilots matched for other normal visual characteristics. The number of times each subject could reestablish fusion while viewing an anaglyph target through alternating 16 delta base-out and 4 delta base-in prism lenses was recorded over a 1-minute time interval. We found the pilot's ability to initiate and sustain fusional vergence movements to be similar to that of their nonrated military counterparts. Our work does not indicate that this test of visual efficiency would discriminate between the pilots and nonpilots in our sample if it were included in a test battery to identify individuals with exceptional visual proficiency.