2003 IMTA Proceedings - International Military Testing Association

PERCEPTUAL DRIFT RELATED TO SPATIAL DISORIENTATION
GENERATED BY MILITARY SYSTEMS :
POTENTIAL BENEFITS OF SELECTION AND TRAINING
Corinne Cian a , Jérôme Carriot b & Christian Raphel a
a Département des facteurs humains, Centre de Recherches du Service de Santé des Armées,
Grenoble, France.
b UPR-ES 597 Sport et Performance Motrice, Université Joseph Fourier, UFRAPS, Grenoble,
France.
The development of new technologies in the weapon systems generate sensory flows
that can induce sensory conflicts and dysfunction. The consequences can be pathological
disorders but beside these extreme cases, the most common consequence is spatial
disorientation. Spatial disorientation is characterized by the failure of the operator to sense
correctly the position or motion of an object or himself within a fixed coordinate system
provided by the surface of the earth and the gravitational vertical. For example spatial
disorientation may induce a misperception of the location of a visual target resulting in a
perceptual drift. This phenomenon may be related to the functional properties of the Central
Nervous System. The object location requires information about the body orientation of the
subject. Then the perceived location depend on visual vestibular and somaesthetic
information. Thus, when the relationship between an observer and the gravitational frame of
reference is altered as when subject is tilted with respect to the gravity or when the magnitude
or direction of the gravity change as often occurs in accelerating vehicle the apparent
locations of seen objects are usually altered (Cohen, 2002).
Most of these problems has been studied in the field of aviation and concerned large
gravito-inertial forces. However, perceptual drifts have been observed for lower gravitoinertial
forces generated by antiaircraft guns. In this system the subject rotated and or is tilted
together with the system. These very low body rotations unconsciously affect the spatial
perception of a target. This perceptual drift may be related to the oculogravic illusion
phenomenon already observed in operational aviation environments.
To study this illusion in a laboratory we generally ask the subject to determine whether
a given target is above or below the level of his eyes. For an upright subject, a target is
considered to be at eye level when an imaginary line connecting the target to the eyes is
perpendicular to the direction of gravity. The angular deviation between the visual target set to
appear at eye level and this horizontal plane defines the visually perceived eye level (Dizio et
al., 1997; Matin et al., 1992; Li et al., 1993). The perceived eye level is strongly influenced by
the variation of the gravitational-inertial forces acting on the subject. This is the case when an
upright subject faces toward the center of a centrifuge that rotates at a steady velocity for
some time. A target that remains at true eye level appears to be above its true location. The
oculogravic illusion induces a lowering of the visually perceived eye level (Cohen, 1973;
Cohen et al., 2001; Graybiel, 1952; Whiteside et al., 1965). This illusion is explained by an
illusory perception of body tilt in pitch related for higher gravito-inertial force changes to a
mechanical action on the otolithic organs of the vestibular system, as well as of the muscle
and cutaneous proprioceptors (Cohen, 1973; Wade et al., 1971), whereas bodily senses
affected by very limited variations of G are restricted, the lowering of the perceived eye level
is probably due to the stimulation of the otolithic system alone (Raphel et al., 1994, 1996).
In the range of very low gravitational-inertial stimulation, there were large individual
differences. The gravitational-inertial disturbances did not induce the same negative
45 th Annual Conference of the International Military Testing Association
Pensacola, Florida, 3-6 November 2003
91