INTRODUCTION:Next-generation air force operations increasingly depend on advanced flight systems, which raises questions about their impact on aircrew workload. Physiological measures enable continuous, objective, and unobtrusive assessments, overcoming some limitations of self-report measures. We investigated whether electroencephalogram, electrocardiogram, and electrodermal activity predicted subjective Rating Scale of Mental Effort (RSME) ratings of fighter pilots during an operationally relevant mission in an F-16 simulator. METHODS:The mission included three flight segments expected to induce increasingly higher workload, with a mathematical task of two arithmetic difficulty levels added to each segment. This approach allowed us to explore whether physiology distinguished workload both across and within flight segments. RESULTS:Subjective ratings confirmed an increase in workload throughout the mission (ΔRSME = 22). However, our manipulation of arithmetic difficulty was less effective: neither subjective ratings nor arithmetic performance significantly differentiated simple and complex calculations (ΔRSME = 5; Δreaction time = 0.02 s, Δunsuccessful trials = 0.5). None of our physiological measures-frontal theta power (Δ0.08, Δ-0.07 mV), parietal alpha power (Δ-0.16, Δ0.14 mV), heart rate (Δ0.01, Δ-0.02 bpm), skin conductance response (Δ0.0, Δ0.0 mS), and skin conductance peaks (Δ0.3, Δ0.2)-systematically distinguished flight segments or arithmetic difficulty, respectively. Physiology also did not significantly predict subjective workload (R2 = 2.2%). DISCUSSION:Large interindividual variability, use of workload management strategies, and relatively small task demand differences may explain the null results. Our study underscores the complexity of workload assessment in an operational setting and offers methodological insights that may inform future ecologically valid research. Reuten AJC, Bruin J, Ledegang WD, Groen EL, Houben MMJ, Cornelisse E-J, Bottenheft C. Physiological and subjective assessment of fighter pilot mental workload. Aerosp Med Hum Perform. 2026; 97(8):592-600.

OBJECTIVE:We examined whether active head aiming with a Helmet Mounted Display (HMD) can draw the pilot's attention away from a primary flight task. Furthermore, we examined whether visual clutter increases this effect. BACKGROUND:Head up display symbology can result in attentional tunneling, and clutter makes it difficult to identify objects. METHOD:Eighteen military pilots had to simultaneously perform an attitude control task while flying in clouds and a head aiming task in a fixed-base flight simulator. The former consisted of manual compensation for roll disturbances of the aircraft, while the latter consisted of keeping a moving visual target inside a small or large head-referenced circle. A "no head aiming" condition served as a baseline. Furthermore, all conditions were performed with or without visual clutter. RESULTS:Head aiming led to deterioration of the attitude control task performance and an increase of the amount of roll-reversal errors (RREs). This was even the case when head aiming required minimal effort. Head aiming accuracy was significantly lower when the roll disturbances in the attitude control task were large compared to when they were small. Visual clutter had no effect on both tasks. CONCLUSION:We suggest that active head aiming of HMD symbology can cause attentional tunneling, as expressed by an increased number of RREs and less accuracy on a simultaneously performed attitude control task. APPLICATION:This study improves our understanding in the perceptual and cognitive effects of (military) HMDs, and has implications for operational use and possibly (re)design of HMDs.

ObjectiveWe aimed to find objective measures of the impact of spatially disorienting (SD) stimuli on pilot cognition in an ecologically valid environment.BackgroundSD frequently occurs in military rotary-wing operations and often contributes to mishaps. Effects of SD stimuli on pilots are usually quantified using control errors, but effects on cognition have not yet been successfully quantified.MethodMilitary helicopter pilots (n = 14) performed scenarios with six SD stimuli (SD condition) and six corresponding control stimuli (NoSD condition) in a motion-base simulator with integrated virtual reality headset. SD stimuli were: false horizon, featureless terrain, leans, brownout, a somatogyral yaw illusion, and loss of horizon due to night vision goggles (NVGs). Mental workload was measured using auditory arithmetic task performance and attentional focus was measured using eye-tracking.ResultsAverage arithmetic task performance was significantly impaired, and proportional gaze dwell time on the attitude indicator was significantly increased in the SD compared to the NoSD condition. Of the six SD stimuli, the featureless terrain, the leans, and the brownout induced significant effects on performance, whereas the featureless terrain, brownout, and false horizon significantly affected gaze behavior. The NVGs and somatogyral yaw stimuli did not induce significant effects. Pilots' self-reports indicated awareness of all SD stimuli, except for the featureless terrain.ConclusionThe results indicate that SD impacts pilot mental workload and attentional focus.ApplicationModern military aircraft present a large volume of mission-related information to pilots. This study shows that SD stimuli may negatively impact the processing of such information.

Data from two simulator experiments were examined to investigate whether performing an auditory task influences pilots' gaze behaviour. Gaze behaviour was measured while participants performed a manual flying task with an auditory task (dual-task condition) or without (single-task condition). Experiment 1 took place in a fixed-base, fixed-wing simulator with 15 novice military pilots. Experiment 2 took place in a moving-base, rotary-wing simulator with 13 experienced military helicopter pilots. Percentage dwell time outside significantly increased in the dual-task condition compared to the single-task condition in both experiments, by a factor of 1.2 and 1.5 respectively. Mean duration of fixations outside significantly increased for pilots, while it decreased for novices. In novices, altitude control performance was also significantly reduced when performing the auditory task, whereas bank angle control performance significantly increased in experienced pilots. The impact on gaze behaviour may potentially serve as a behavioural indicator of pilot auditory workload.

INTRODUCTION: The illusions of head motion induced by galvanic vestibular stimulation (GVS) can be used to compromise flight performance of pilots in fixed-base simulators. However, the stimuli used in the majority of studies fail to mimic disorientation in realistic flight because they are independent from the simulated aircraft motion. This study investigated the potential of bilateral-bipolar GVS coupled to aircraft roll in a fixed-base simulator to mimic vestibular spatial disorientation illusions, specifically the “post-roll illusion” observed during flight.METHODS: There were 14 nonpilot subjects exposed to roll stimuli in a flight simulator operating in a fixed-base mode. GVS was delivered via carbon rubber electrodes on the mastoid processes. The electrical stimulus was driven by the high-pass filtered aircraft roll rate to mimic the semicircular canals’ physiological response. The post-roll test scenarios excluded outside visual cues or instruments and required subjects to actively maintain a constant bank angle after an abrupt stop following a passive prolonged roll maneuver. The anticipated outcome was an overshot in roll elicited by the GVS signal.RESULTS: The responses across subjects showed large variability, with less than a third aligning with the post-roll illusion. Subjective ratings suggest that the high-pass filtered GVS stimuli were mild and did not induce a clear sense of roll direction. However, uncontrolled head movements during stimulation might have obscured the intended effects of GVS-evoked illusory head movements.CONCLUSION: The mild and transient GVS stimuli used in this study, together with the uncontrolled head movements, did not convincingly mimic the post-roll illusion.Houben MMJ, Stuldreher IV, Forbes PA, Groen EL. Using galvanic vestibular stimulation to induce post-roll illusion in a fixed-base flight simulator. Aerosp Med Hum Perform. 2024; 95(2):84–92.

BACKGROUND Previous research has shown that experiencing motion stimuli negatively impacts cognitive performance. OBJECTIVE In the current study, we investigate whether this impact relates to Type-II spatial disorientation (SD), to motion stimulus magnitude, or to an interaction of these factors. METHOD Stimuli for participants (n = 23) consisted of Earth-vertical yaw rotations on a rotating chair in a completely darkened room. In the surprise condition, the stimulus started with subthreshold acceleration, followed by suprathreshold deceleration to a non-zero velocity, inducing a sensation of rotation that is opposite to the actual rotation revealed when the lights were switched on. In the no-surprise condition, the same changes in velocity were used, but starting from (almost) zero velocity, which induced a sensation of rotation in the same direction as the actual rotation. Participants performed a self-paced arithmetic task and measurement of their cognitive performance started after the environment was revealed. Stimulus magnitude was operationalized through higher or lower peak suprathreshold deceleration. RESULTS The results revealed that counting speed decreased significantly when participants were surprised, constituting a large effect size. The proportion of counting errors likewise increased significantly when participants were surprised, but only in the high-magnitude condition. APPLICATION The findings suggest that surprise caused by the recognition of SD has an involuntary disruptive effect on cognition, which may impact performance of piloting tasks. These results are relevant when modeling motion stimuli effects on performance, and when developing SD awareness training for pilots.

BACKGROUND: In this study, we investigated the impact of a loss of horizon due to atmospheric conditions on flight performance and workload of helicopter pilots during a low-altitude, dynamic flight task in windy conditions at sea. We also examined the potential benefits of a helmet-mounted display (HMD) for this specific task. METHODS: In a fixed-based helicopter simulator, 16 military helicopter pilots were asked to follow a maneuvering go-fast vessel in a good visual environment (GVE) and in a degraded visual environment (DVE). DVE was simulated by fog, obscuring the horizon and reducing contrast. Both visual conditions were performed once with and once without an HMD, which was simulated by projecting head-slaved symbology in the outside visuals. Objective measures included flight performance, control inputs, gaze direction, and relative positioning. Subjective measures included self-ratings on performance, situation awareness, and workload. RESULTS: The results showed that in DVE the pilots perceived higher workload and were flying closer to the go-fast vessel than in GVE. Consequently, they responded with larger control inputs to maneuvers of the vessel. The availability of an HMD hardly improved flight performance but did allow the pilots to focus their attention more outside, significantly improving their situation awareness and reducing workload. These benefits were found in DVE as well as GVE conditions. DISCUSSION: DVE negatively affects workload and flight performance of helicopter pilots in a dynamic, low-altitude following task. An HMD can help improve situation awareness and lower the workload during such a task, irrespective of the visual conditions. Ledegang WD, van der Burg E, Valk PJL, Houben MMJ, Groen EL. Helicopter pilot performance and workload in a following task in a degraded visual environment . Aerosp Med Hum Perform. 2024; 95(1):16–24.

This study investigates how cognitive performance is affected by the combination of two stressors that are operationally relevant for helicopter pilots: heat load and hypobaric hypoxia. Fifteen participants were exposed to (1) no stressors, (2) heat load, (3) hypobaric hypoxia, and (4) combined heat load and hypobaric hypoxia. Hypobaric hypoxia (13,000 ft) was achieved in a hypobaric chamber. Heat load was induced by increasing ambient temperature to ∼28 °C. Cognitive performance was measured using two multitasks, and a vigilance task. Subjective and physiological data (oxygen saturation, heart rate, core- and skin temperature) were also collected. Mainly heat load caused cognitive performance decline. This can be explained by high subjective heat load and increased skin temperature, which takes away cognitive resources from the tasks. Only the arithmetic subtask was sensitive to hypobaric hypoxia, whereby hypobaric hypoxia caused a further performance decline in addition to the decline caused by heat load.Practitioner summary: Little is known about how multiple environmental stressors interact. This study investigates the combined effects of heat load and hypobaric hypoxia on cognitive performance. An additive effect of heat load and hypobaric hypoxia was found on a arithmetic task, which may be attributed to independent underlying mechanisms.

(1) Background: It is difficult for accident investigators to objectively determine whether spatial disorientation may have contributed to a fatal airplane accident. In this paper, we evaluate three methods to reconstruct the possible occurrence of the somatogravic illusion based on flight data recordings from an airplane accident. (2) Methods: The outputs of two vestibular models were compared with the “standard” method, which uses the unprocessed gravito-inertial acceleration (GIA). (3) Results: All three methods predicted that the changing orientation of the GIA would lead to a somatogravic illusion when no visual references were available. However, the methods were not able to explain the first pitch-down control input by the pilot flying, which may have been triggered by the inadvertent activation of the go-around mode and a corresponding pitch-up moment. Both vestibular models predicted a few seconds delay in the illusory tilt from GIA due to central processing and sensory integration. (4) Conclusions: While it is difficult to determine which method best predicted the somatogravic illusion perceived during the accident without data on the pilot’s pitch perception, both vestibular models go beyond the GIA analysis in taking into account validated vestibular dynamics, and they also account for other vestibular illusions. In that respect, accident investigators would benefit from a unified and validated vestibular model to better explain pilot actions in accidents related to spatial disorientation.

BACKGROUND: The vestibular Coriolis illusion is a disorienting sensation that results from a transient head rotation about one axis during sustained body rotation about another axis. Although often used in spatial disorientation training for pilots and laboratory studies on motion sickness, little is known about the minimum required rotation rate to produce the illusion. OBJECTIVE: This study determined the perception threshold associated with the Coriolis illusion. METHODS: Nineteen participants performed a standardized pitching head movement during continuous whole-body yaw rotation at rates varying between 5 to 50 deg/s. The participants reported their motion sensation in relation to three hypothesized perception thresholds: 1) a sense of undefined self-motion, 2) a sense of rotation, and 3) a sense of rotation and its direction (i.e., the factual Coriolis illusion). The corresponding thresholds were estimated from curves fitted by a generalized linear model. RESULTS: On average threshold 1 was significantly lower (8 deg/s) than thresholds 2 and 3. The latter thresholds did not differ from each other and their pooled value was 10 deg/s. CONCLUSIONS: The Coriolis illusion is perceived at yaw rates exceeding 10 deg/s using a pitching head movement with 40 deg amplitude and 55 deg/s peak velocity. Model analysis shows that this corresponds to an internal rotation vector of 6 deg/s. With this vector the Coriolis perception threshold can be predicted for any other head movement.

In a laboratory study, the indoor annoyance caused by the sound produced by aircraft during the takeoff on the runway is investigated. This aircraft sound is dominated by relatively high sound levels in the 16 and 31.5 Hz octave bands. Road-traffic and passenger railway sounds, which lack high sound levels in these octave bands, are included as references. The sounds are presented at indoor A-weighted equivalent levels of 32 and 42 dB. The participants are males and females between 20 and 40, or between 40 and 60 years of age. The indoor annoyance increased with sound level, but it was not affected by source type. Moreover, it was not or hardly affected by gender or age. With the dose expressed as A-weighted outdoor levels, the penalty for the aircraft sound and the bonus for the passenger railway sound at least qualitatively correspond to those obtained in pertinent previous studies. In the present study, such adjustments can be avoided by including the difference between the outdoor C-weighted and A-weighted levels as a second predictor, yielding an explained variance in the mean indoor annoyance ratings as high as 98%.

Eye movements analysis has great potential for understanding operator behaviour in many safety-critical domains, including aviation. In addition to traditional eye-tracking measures on pilots’ visual behavior, it seems promising to incorporate machine learning approaches to classify pilots’ visual scanning patterns. However, given the multitude of pattern measures, it is unclear which are better suited as predictors. In this study we analyzed the visual behaviour of eight pilots, flying different flight phases in a moving-base flight simulator. With this limited dataset we present a methodological approach to train linear Support Vector Machine models, using different combinations of the attention ratio and scanning pattern features. The results show that the overall accuracy to classify the pilots’ visual behaviour in different flight phases, improves from 51.6% up to 64.1% when combining the attention ratio and instrument scanning sequence in the classification model.

BACKGROUND:During large angles of self-tilt in the roll plane on Earth, measurements of the subjective visual vertical (SVV) in the dark show a bias towards the longitudinal body axis, reflecting a systematic underestimation of self-tilt.OBJECTIVE:This study tested the hypothesis that self-tilt is underestimated in partial gravity conditions, and more so at lower gravity levels.METHODS:The SVV was measured in parabolic flight at three partial gravity levels: 0.25, 0.50, and 0.75 g. Self-tilt was varied amongst 0, 15, 30, and 45 deg, using a tiltable seat. The participants indicated their SVV by setting a linear array of dots projected inside a head mounted display to the perceived vertical. The angles of participants' body and head roll tilt relative to the gravito-inertial vertical were measured by two separate inertial measurement units.RESULTS:Data on six participants were collected. Per G-level, a regression analysis was performed with SVV setting as dependent variable and head tilt as independent variable. The latter was used instead of chair tilt, because not all the participants' heads were aligned with their bodies. The estimated regression slopes significantly decreased with smaller G-levels, reflecting an increased bias of the SVV towards the longitudinal body axis. On average, the regression slopes were 0.95 (±0.38) at 0.75 g; 0.84 (±0.22) at 0.5 g; and 0.63 (±0.33) at 0.25 g.CONCLUSIONS:The results of this study show that reduced gravity conditions lead to increased underestimation of roll self-tilt.

BACKGROUND: Spatial disorientation (SD) remains a significant cause of accidents and near accidents. A variety of training methods have been used to assist pilots to anticipate the SD problem. The value of such training in the prevention of disorientation has been difficult to assess.METHODS: To study transfer of SD awareness training, we related reported incidents to the content and frequency of SD awareness training received. The questionnaire was completed by 368 out of 495 pilots; 189 currently flying fixed-wing, and 150 flying rotary-wing aircraft. On average, their age was 38, and they had 2466 flight hours on-type.RESULTS: Respondents gave high ratings for the importance of SD training and their awareness of SD, the latter being one of the training objectives. The amount of SD training received by respondents was positively correlated with ratings for appreciation and importance. Self-rated awareness was positively correlated with the number of reported SD experiences. Although the correlations were below 0.50, the results provide an indication that SD training is effective. In total, respondents reported 5773 SD experiences, 195 of them resulting in a serious risk for flight safety. Narratives of these serious events show that, in many cases, pilots managed their SD by carefully checking the flight instruments, and also by good crew coordination.DISCUSSION: The results of the survey provide some evidence, although based on subjective reports, for transfer of SD training. The results of the SD experiences can be used to improve the SD training in terms of content and frequency.Pennings HJM, Oprins EAPB, Wittenberg H, Houben MMJ, Groen EL. Spatial disorientation survey among military pilots. Aerosp Med Hum Perform. 2020; 91(1):4-10.

Car handling, and hence, safety, is affected by the way we estimate speed. Speed, however, is often underestimated in degraded visual environments, including virtual environments such as driving simulators. In simulators the visual and physical motion are typically incongruent as limited by quality and amplitude, respectively, which may cause a negative transfer of training. To improve the (training) quality of simulators and make them feel more real, it would be helpful to fill a knowledge gap on in-car speed perception as affected by real and virtual views, within a single group of subjects. We did so by testing whether estimations of speed in terms of km/h could be a valid metric for that purpose. We therefore exposed 17 subjects, seated as passengers in the front of a car on a straight road to four experimental conditions: (1) driving with a real out-the-window view, (2) driving with a live video view, (3) standing still watching pre-recorded video's, and (4) driving with eyes closed. Field-of-view was made equal in all conditions. Speeds tested ranged between 20 and 60 km/h. On average, speed was estimated 5 km/h less than actual, while we did not find a statistically significant difference between the four conditions tested. These results seem to contradict previous observations on motion perception, in particular in simulators, that have been ascribed to the quality of the visuals used. This finding may yet be explained by the assumption that speed estimations in terms of km/h are dominated by (conscious) cognitive processes, while visual-vestibular coherence between visual and physical motion, is dominated by (unconscious) sensorial driven perceptual processes. This disqualifies perceived speed as a valid metric for studying motion perception related to the optimisation of simulators.

BACKGROUND: Royal Netherlands Air Force (RNLAF) helicopter aircrew get Helicopter Underwater Egress Training (HUET) using a Modular Egress Training Simulator (METS™) in order to be prepared for escaping the aircraft when ditching into water. In the current situation the retraining intervals are only chosen on an arbitrary basis for different backgrounds of the crew (maritime and regular flight crew). The frequency of refresher training depends on the expected degree of retention, but evidence-based research on required intervals between refresher courses is scarce. Ideally, training should be based on the amount of retention of acquired competencies.METHODS: Retrospective questionnaires were filled in by 132 helicopter aircrew who followed the HUET course(s) at the Survival Evasion Resistance and Escape (SERE) school in Gilze-Rijen (Netherlands). They assessed themselves on competencies and gave their opinion on the preferred interval.RESULTS: Maritime crew report increasing competence levels with the number of refresher courses followed. According to the opinion of all aircrew, retraining intervals may take longer than 18 (first refresher) to 30 mo (fourth refresher). Maritime and regular flight crew differ in preferred retraining intervals (up to 22 mo and up to 33 mo, respectively).DISCUSSION: This study provides indications to reconsider the retraining interval and to differentiate between maritime and regular flight crew based on aircrew's opinions and self-assessments. As competence levels still increase with the number of courses followed, it is recommended to reconsider the current fixed intervals of once a year or once every 3 yr for maritime and regular flight crew, respectively.Bottenheft C, Oprins EAPB, Houben MMJ, Meeuwsen T, Valk PJL. Self-assessed preferred retraining intervals of Helicopter Underwater Egress Training (HUET). Aerosp Med Hum Perform. 2019; 90(9):800-806.

TNO and Boeing developed a “Spatial Disorientation Identification Tool” (SDiT) to support the investigation of recorded aircraft motion for its potential to induce Spatial Disorientation (SD). The tool is based on a perception model that consists of transfer functions representing the dynamics in the vestibular system (semicircular canals and otoliths) and their neural interaction. We extended this perception model with an algorithm to identify different vestibular illusions from the computed mismatch between the perceived and actual aircraft orientation. The model is integrated in a graphical user interface that allows the user to control the analysis, for example by adjusting some of the model parameters within validated ranges. The interface also shows an animation of the actual and perceived aircraft attitude. SD illusions that are being recognized by the tool are the “somatogyral illusion,” resulting from erroneous perception of aircraft rotations; and the “somatogravic illusion,” resulting from ambiguities between linear accelerations and attitude. The tool was validated using recordings of basic flight maneuvers, and also with data of an actual Loss of Control In-flight (LOC-I) accident. Combined with other data, e.g., control inputs, the SDiT can help to make sense of pilot actions in accidents and incidents. © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

With modern trends of decrease in crew numbers on board ships together with increased operational demands and paperwork, crew fatigue and comfort have become more critical and are being given more importance. It is well known that environmental factors affect crew comfort and performance. The two outstanding factors which exist in the shipboard environment are vessel motions and noise. As such, the findings and lessons learnt from other industrial sectors are considered to be less relevant for ships. Therefore, it is necessary to conduct focused research to understand the effects of these factors, so that the lessons learnt can be integrated into the ship design process so as to mitigate their adverse effects during vessel operations. Due to obvious performance issues, ship motions and motion sickness research has attracted far more interest than human response to noise. This paper reports the findings of a recent research study undertaken as part of an EU FP7 research project, namely SILENV, which investigated the current levels of crew noise exposure through field studies. Furthermore, developed models on human response to noise on board ships and SILENV Green Label noise standards are also introduced in comparison with the current normative framework.

Forensic professionals have to collect evidence at crime scenes quickly and without contamination. A handheld Augmented Reality (AR) annotation tool allows these users to virtually tag evidence traces at crime scenes and to review, share and export evidence lists. In an user walkthrough with this tool, eight end-users annotated a virtual crime scene while thinking aloud. Qualitative results show that annotation could improve orientation on the crime scene, speed up the collection process and diminish administrative pressure. While the current prototype suffered from technical limitations due to slow feature tracking, AR annotation was found to be a promising, usable and valuable tool in crime scene investigation.

In the present study relations between the level of impulse sounds and the observed proportion of behaviorally confirmed awakening reactions were determined. The sounds (shooting sounds, bangs produced by door slamming or by container transshipment, aircraft landings) were presented by means of loudspeakers in the bedrooms of 50 volunteers. The fragments for the impulse sounds consisted of single or multiple events. The sounds were presented during a 6-h period that started 75 min after the subjects wanted to sleep. In order to take account of habituation, each subject participated during 18 nights. At equal indoor A-weighted sound exposure levels, the proportion of awakening for the single impulse sounds was equal to that for the aircraft sounds. The proportion of awakening induced by the multiple impulse sounds, however, was significantly higher. For obtaining the same rate of awakening, the sound level of each of the successive impulses in a fragment had to be about 15-25 dB lower than the level of one single impulse. This level difference was largely independent of the degree of habituation. Various explanations for the enhanced awakening probability are discussed.