During flight in aircraft and spacecraft, pilots are regularly subjected to unusual force environments. These forces not only influence a variety of pressure-sensitive mechanisms but, in particular, they stimulate the vestibular mechanism of the inner ear. The latter source of information regarding spatial orientation may be in accord with information from direct visual stimulation or it may be in conflict with it. In the first case, veridical space perception may be expected, while in the second the perception is frequently nonveridical. This results in constant errors in judgment with respect to motion of visual objects and in the pilot's estimates of the objects' position. These errors, referred to by pilots as “vertigo,” are believed to be of importance in piloting aircraft and spacecraft where the pilot's task involves actions based on visual space perception.