ORIGIN AND PROCESSING OF POSTURAL INFORMATION

This contribution surveys the sources and the processing of spatial in formation about posture, that is, about the orientation of the body an d its parts with respect to the vertical (whereas 'position' designate s their orientation to each other). Postural information is, to a cons iderable extent, gained by sense organs in the head. Hence information gained by the mobile eyes and the pitched-up labyrinths is first tran sformed from a retinal and otolithic into a head-fixed frame of refere nce, then from head-to trunk-fixed coordinates, and, finally, from a t runk-fixed to an exocentric frame of reference. To that end the positi on of eyes and otoliths to the head, of the head to the trunk, and of the trunk to the rest of the world must be known, deduced by efference copies or measured by proprioceptors. It is shown that the perceived relation of the visual world to the vertical is exclusively determined by sense organs in the head? whereas body posture is also directly me asured by recently discovered graviceptors in the human trunk. It appe ars that the proprioceptors mediate perception of position, but not, o r only indirectly, of posture. (C) 1998 Elsevier Science Ltd. All righ ts reserved.