Some influences of touch and pressure cues on human spatial orientation.

During constant velocity rotation about his recumbent Z axis, a blindfolded subject feels as if he were on an orbital path in the same direction. This experienced motion results from the pattern of touch and pressure stimulation of the body surface. If the subject changes the pressure pattern on his body by bracing himself in the rotating apparatus in different ways, it is possible for him to influence profoundly and systematically his apparent orientation. For example, pressure on the top of his head while he is rotating can make the subject feel he is upside down on a cylindrical path. The changes in apparent ongoing posture elicited by different patterns of pressure cues are very similar for different subjects and are constant for the same subject over time. During experienced orbital motion, a subject will hear a continuously emitting sound source--one that is stationary in the external environment--as circling his head in the direction opposite that of his true rotation. If the rotating subject is permitted unrestricted sight of his surroundings, he neither experiences orbital motion nor mislocalizes sounds. These observations provide insight into the spatial orientation mechanisms that normally allow an organism to distinguish accurately between those changes in activity at its receptors contingent on its own movements, and those resulting from movement within the environment. They also provide a way of understanding some of the postural illusions experienced during exposure to unusual force environments, including free fall.