Physiological responses to the Coriolis illusion: effects of head position and vision.
BACKGROUND
Changes in sympathetic outflow during Type II spatial disorientation are well documented. In this study we investigated the influences of head position and eye state (open or closed) on sympathetic activation.


METHODS
There were 11 naive subjects (6 men, 5 women) who were tested in a General Aviation Trainer that accelerated at a subthreshold rate for 60 s until a constant angular velocity of 90 degrees x s(-1) was reached. Approximately 40 s later, subjects were instructed to tilt their heads along either the pitch or roll axis, stimulating a Coriolis illusion. Subjects reported the perceived intensity and duration of disorientation. Heart rate, heart rate variability, and electrodermal responses were recorded before, during, and after the period of disorientation. Each subject completed four trials, which were crossed combinations of head position and eye state.


RESULTS
There were significant increases in heart rate and the electrodermal response during disorientation, but no significant change in heart rate variability. Head position had no significant effect on any physiological parameters or on the perceived intensity of disorientation; subjects reported a shorter duration of disorientation when the head was tilted into the roll versus the pitch axis. Eye state had no effect on heart rate, heart rate variability, or the intensity of disorientation, but the electrodermal response was somewhat greater, and the duration of disorientation shorter when eyes were open.


CONCLUSIONS
The results suggest that head position and eye state (open or closed) do not need to be included as factors when investigating sympathetic outflow during a mild Coriolis illusion.
Westmoreland
David
D
Department of Biology, 2355 Faculty Drive, Suite 2P389, US Air Force Academy, CO 80840, USA. david.westmoreland@usafa.edu
Krell
Robert W
RW
Self
Brian P
BP
D000328:Adult; D000337:Aerospace Medicine; D003312:Coriolis Force; D005133:Eye Movements / Q000502:physiology*; D005260:Female; D019416:Head Movements / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D007088:Illusions / Q000502:physiology*; D008297:Male; D009949:Orientation