Rolling into Spatial Disorientation: Simulator Demonstration of the Post-Roll (Gillingham) Illusion

Abstract

Introduction: Spatial disorientation (SD) is still a contributing factor in many aviation accidents, stressing the need for adequate SD training scenarios. In this article we focused on the post-roll effect (the sensation of rolling back after a roll maneuver, such as an entry of a coordinated turn) and investigated the effect of roll stimuli on the pilot's ability to stabilize their roll attitude. This resulted in a ground-based demonstration scenario for pilots. Methods: The experiments took place in the advanced 6-DOF Desdemona motion simulator, with the subject in a supine position. Roll motions were either fully automated with the subjects blindfolded (BLIND), automated with the subject viewing the cockpit interior (COCKPIT), or self-controlled (LEAD). After the roll stimulus subjects had to cancel all perceived simulator motion without any visual feedback. Both the roll velocity and duration were varied. Results: In 68% of all trials subjects corrected for the perceived motion of rolling back by initiating a roll motion in the same direction as the preceeding roll. The effect was dependent on both rate and duration, in a manner consistent with semicircular canal dynamics. The effect was smallest in the BLIND scenario, but differences between simulation scenarios were non-signifi cant. Discussion: The results show that the effects of the postroll illusion on aircraft control can be demonstrated adequately in a fl ight simulator using an attitude control task. The effect is present even after short roll movements, occurring frequently in fl ight. Therefore this demonstration is relevant for spatial disorientation training programs for pilots.

Roll aftereffects: influence of tilt and inter-stimulus interval

“…A RAE has previously been described in pilots flying aircraft (Ercoline et al 2000) as well as in flight simulators (Nooij and Groen 2011). However, these previous studies were focused on developing techniques for pilot training rather than characterizing the RAE itself.…”

“…In the current experiments the direction of gravity provides a potential cue to roll direction. In prior studies the subject was oriented nose up (Nooij and Groen 2011) or the roll was due to a coordinated turn (Ercoline et al 2000) so that the orientation of the gravity vector did not change relative to the subject. Since in our everyday experiences we are upright and head roll is associated with changes in the gravity vector it is important to understand the influence of gravity.…”

“…Thus, the post-roll illusion is essentially a sensory aftereffect although it has not classically been considered in those terms. The phenomenon has been hypothesized to be the cause of several aviation accidents (Lyons et al 1994), and has been demonstrated in aircraft during controlled conditions (Ercoline et al 2000) as well as in simulated flight conditions which demonstrated the effect even after rolls as short as 2 s (Nooij and Groen 2011). Various terms have been used for this phenomenon: Gillingham illusion, post-roll illusion, and roll aftereffect.…”

“…The RAE has previously been studied only in an aviation context so that the main outcome is the amount of force applied to a control stick (Nooij and Groen 2011) or the bank angle the subject oriented a plane after a turn (Ercoline et al 2000). In these prior studies many (Nooij and Groen 2011) or all (Ercoline et al 2000) of the subjects also had pilot training which almost certainly influenced their responses given the context of the experiments.…”

“…Thus, sensation of tilt is absent and in the absence of visual feedback and instruments the semicircular canals provide the only cue to roll. When the RAE was previously studied in a flight simulator it was done with the subject on their back so that roll could be delivered without changes with respect to the gravity vector (Nooij and Groen 2011). Furthermore, even when the gravity vector is tilted, the orientation of a surrounding visual environment, such as the inside of an aircraft cabin, leads to a strong perception that one’s orientation is upright (Howard and Hu 2001; Groen et al 2002).…”