Integration of somatosensory and vestibular inputs in perceiving the direction of passive whole-body motion

Abstract

We investigated the contribution of somatosensory and vestibular inputs in the detection of the direction of linear whole-body displacement (1.5 m) at low levels of linear acceleration (peak acceleration 0.2 m/s 2), in normal subjects. Subjects sat on a mobile robot wearing opaque goggles and headphones. They indicated the direction of motion by using a laser pointer held by the right hand at the level of the chin. Adaptation to a long-lasting static head turn (45° to the right) was used to modify the perceived head orientation relative to the trunk. After about 15 min the head and trunk were perceived to be aligned with each other. After adaptation subjects pointed in the same direction as in the control condition in spite of the change in the perception of the head orientation. Because space orientated reactions to vestibular stimuli were previously shown to be coded in the perceived head reference frame, these results indicate that somatosensory cues are also integrated in the perception of linear motion. Unexpectedly, after adaptation, trunk and head perceived orientations were attracted toward the direction of the imposed motion. This suggests that the internal representation of body configuration depends also upon available cues from the extrapersonal space.