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Meeting Abstract

Somatogyral illusions during flight: effect of the post-roll illusion on pilot’s control behaviour

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Nooij, S., & Groen, E. (2010). Somatogyral illusions during flight: effect of the post-roll illusion on pilot’s control behaviour. Journal of Vestibular Research, (20), 215-216.

Cite as: https://hdl.handle.net/11858/00-001M-0000-0013-BF08-B
Background: Due to the high-pass characteristics of
the semicircular canals, the rotation sensation dies out
during constant velocity rotation, and a sensation of rotation in the opposite direction arises when the rotation
stops. This phenomenon is known as the somatogyral
illusion. A model of the semicircular canal dynamics
predicts that the magnitude of this illusion depends
on the amount of per-rotary response-decay. This has
been extensively studied for rotations about the vertical
yaw axis, where the rate of decay is relatively low
(due to velocity storage). In roll – where the sense of
counter rotation is referred to as the post-roll illusion –
the situation is different. Due to the absence of velocity
storage the response-decay is faster, and noticeable
after-effects may occur after shorter movements than
in yaw. This has implications for flying, where short
roll movements occur frequently. When unnoticed, the
post-roll illusion may trigger the pilot to give erroneous
control inputs leading to excessive aircraft bank.
Objectives: We hypothesized that the post-roll illusion
is determined by both the duration and angular rate of
roll motion. We investigated this by studying the effect
of different roll stimuli on the control inputs of pilots
who actively stabilized the aircraft bank in a movingbase
spatial disorientation trainer.
Methods: In flight roll manoeuvres are often coordinated,
meaning that the gravito-inertial vector is always
aligned with the pilot, and the graviceptors do not
provide roll cues. When aircraft roll is simulated by
simply tilting a simulator relative to gravity this will
give the sensation of uncoordinated flight, or sideslip.
For that reason, we tilted the simulator backward as to
orient the subject in a supine position with his roll-axis
being earth vertical. In this situation, simulator rollwas
independent of gravity, simulating coordinated flight.
Subjects (n = 15) were exposed to six different motion
profiles (reference condition, 10◦/s for 12 s, 30◦/s for
2 and 6s, 60◦/s for 2 and 6s) and were instructed to
“hold attitude” following the roll movement, without
any visual attitude reference. In other words: they had
to cancel all perceived cabin motion following the roll
movement. Three simulation conditions were investigated.
In the first two, subjects were either blindfolded
(BLIND) or viewed the interior of the cockpit (COCKPIT; no outside view or instruments) and roll motion
was automated. In the third condition (LEAD) subjects
actively performed the roll motion by following a lead
aircraft that disappeared in the fog (no visual attitude
information) after the desiredmovement. The subjects’
control input and simulator movement following each
roll movement were recorded.
Results: In general, subjects corrected for the perceived
counter-rotation by inducing a roll in the same
direction as the preceding movement. Effects were
smallest in the BLIND condition and largest in the
LEAD condition where the pilot was in the loop. The
effect increased with roll rate and duration. These
results reflected the semicircular canal dynamics and
were in accordance with a semicircular canal based
motion perception model.
Conclusion: The results indicate that the post-roll illusion
affected the pilot’s ability to maintain a stable
attitude following a roll movement when visual attitude
cues are absent. Although the effect is largest with
sustained rolling motion, it is also present in shorter
movements lasting only 2s. As far as we know, this was
the first successful attempt to reproduce the post-roll
illusion in a ground-based spatial disorientation trainer.
Such demonstration may be useful in demonstrating
this effect to student pilots.