When entering a coordinated flight turn without visual references, the perception of roll-angular displacement is determined by vestibular cues, and/or probably by assessment of the gravitoinertial (G) load (G magnitude) and its translation into the corresponding bank angle. Herein, we examined whether repeated exposures to hypergravity (G training) in a centrifuge, would advance, not only the ability to accurately assess the G load but also the capacity to detect or estimate the corresponding roll inclination of the centrifuge gondola. To this end, in nine men without piloting experience, the subjective estimation of G load and roll tilt were assessed, in complete darkness, during 5-min coordinated turns in the centrifuge, performed at 1.1 G (25 degrees roll-tilt angle) and 2.0 G (60 degrees roll tilt angle). These trials were conducted before and after 5 wk of G training {3 x 40-min sessions<middle dot>wk-1; protocol: 20 x 1 min at G levels close to the individual relaxed G-level tolerance [range: similar to 2.6 G (similar to 67 degrees)-3.6 G (74 degrees)], separated by 1-min intervals at idle speed (1.4 G)}, whereas continual feedback to the subjects was limited to the G load. As expected, G training improved subjects' capacity to assess G load, especially at 2.0 G (P = 0.006). The perception of roll tilt, however, was consistently underestimated (by similar to 70%-80%), and not enhanced by G training (P >= 0.51). The present findings demonstrate that prolonged repeated G-induced roll-tilts in a centrifuge gondola, while external feedback is restricted to graviception, enhance the capacity to perceive G load, but fail to advance the ability to detect or consciously estimate the magnitude of roll-angular displacement during a coordinated turn. NEW & NOTEWORTHY During a coordinated flight turn without external visual references, the pilot typically underestimates the aircraft bank angle, because unreliable information of roll tilt is conveyed by the vestibular system. The present results demonstrate that prolonged repeated gravitoinertial (G)-induced roll-tilts in a centrifuge gondola, while external feedback is restricted to graviception, enhance the capacity to perceive G load, but fail to advance the ability to consciously estimate the magnitude of roll angular displacement.

During coordinated flight and centrifugation, pilots show interindividual variability in perceived roll tilt. The study explored how this variability is related to perceptual and cognitive functions. Twelve pilots underwent three 6-min centrifugations on two occasions (G levels: 1.1G, 1.8G, and 2.5G; gondola tilts: 25°, 56°, and 66°). The subjective visual horizontal (SVH) was measured with an adjustable luminous line and the pilots gave estimates of experienced G level. Afterward, they were interrogated regarding the relationship between G level and roll tilt and adjusted the line to numerically mentioned angles. Generally, the roll tilt during centrifugation was underestimated, and there was a large interindividual variability. Both knowledge on the relationship between G level and bank angle, and ability to adjust the line according to given angles contributed to the prediction of SVH in a multiple regression model. However, in most cases, SVH was substantial smaller than predictions based on specific abilities.

Without visual references, nonpilots exposed to coordinated flight turns underestimate the bank angle, because of discordant information of the roll-angular displacement from the otoliths, consistently signaling vertical position, versus the semicircular canals, enabling detection of the displacement. Pilots may also use their ability to perceive the G load and knowledge of the relation between load and angle to assess the bank angle. Our aim was to investigate whether the perception of bank angle can be improved by spatial orientation training in a centrifuge. Sixteen pilots/pilot students assessed their roll tilt, in complete darkness, during both real coordinated flight turns and gondola centrifugation, at roll tilts of 30◦ and 60◦. The experiments were repeated after a 3-wk period, during which eight of the subjects performed nine training sessions in the centrifuge, comprising feedback on roll angle vs. G load, and on indicating requested angles. Before training, the subjects perceived in the aircraft and centrifuge, respectively: 37 (17)◦, 38 (14)◦ during 60◦ turns and 19 (12)◦, 20 (10)◦ during 30◦ turns. Training improved the perception of angle during the 60◦ [to 60 (7)◦, 55 (10)◦; P ≤ 0.04] but not the 30◦ [21 (10)◦, 15 (9)◦; P ≥ 0.30] turns; the improvement disappeared within 2 yr after training. Angle assessments did not change in the untrained group. The results suggest that it is possible to, in a centrifuge, train a pilot’s ability to perceive large but not discrete-to-moderate roll-angular displacements. The transient training effect is attributable to improved capacity to perceive and translate G load into roll angle and/or to increased reliance on semicircular canal signals. NEW & NOTEWORTHY Spatial disorientation is a major problem in aviation. When performing coordinated flight turns without external visual cues (e.g., flying in clouds or darkness), the pilot underestimates the aircraft bank angle because the vestibular system provides unreliable information of roll tilt. The present study demonstrates that it is possible to, in a long-arm centrifuge, train a pilot’s ability to perceive large but not discrete-to-moderate roll-angular displacements.

BACKGROUND: During a simulated coordinated turn in a gondola centrifuge, experienced pilots show a substantial inter-individual variability in visual measures of perceived roll tilt. Because of the centrifuge's small radius, the pattern of stimuli to the semicircular canals during acceleration of the centrifuge differs in certain respects from that of an aircraft entering a turn.

OBJECTIVE: To explore whether these differences may be of significance for the pilot's roll- plane orientation and whether individual characteristics revealed in the centrifuge correspond to those during real flight.

METHOD: 8 fixed-wing air-force pilots were tested in a centrifuge and a high-performance aircraft. The centrifuge was accelerated to 2 G (gondola inclination 60°) within 10 s. The duration at 2 G was 6 minutes. Similar profiles were created in the aircraft. The subjective visual horizontal (SVH) was measured using an adjustable luminous line in darkness. Each pilot was tested on three occasions: centrifuge (2 runs), aircraft (2 turns), centrifuge (2 runs). For each 2-G exposure, initial and final SVH values were established via curve fitting.

RESULT: Despite a large inter-individual variability (±SD), group means were similar in the aircraft (initial: 43.0±20.6°; final: 22.5±14.8°) and centrifuge (initial: 40.6±17.0°; final: 20.5±16.0°). Further, individual peculiarities in response patterns were similar in the two conditions. For both the initial and final SVH tilt there was a high correlation between centrifuge and aircraft.

CONCLUSION: The correspondence between conditions suggests that the centrifuge is an adequate means for demonstrating the fundamental motion pattern of coordinated flight and also for establishing the individual pilot's ability to perceive an aircraft's roll attitude.Findings are discussed in connection with vestibular learning and the possibility of underlying differences between pilots in the keenness for semicircular canal and somatosensory cues.