INTEGRATION OF SOMATOSENSORY AND VESTIBULAR INPUTS IN PERCEIVING THE DIRECTION OF PASSIVE WHOLE-BODY MOTION

We investigated the contribution of somatosensory and vestibular input s 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 opaq ue goggles and headphones. They indicated the direction of motion by u sing a laser pointer held by the right hand at the level of the chin. Adaptation to a long-lasting static head turn (45 degrees to the right ) was used to modify the perceived head orientation relative to the tr unk. After about 15 min the head and trunk were perceived to be aligne d with each other. After adaptation subjects pointed in the same direc tion as in the control condition in spite of the change in the percept ion of the head orientation. Because space orientated reactions to ves tibular stimuli were previously shown to be coded in the perceived hea d reference frame, these results indicate that somatosensory cues are also integrated in the perception of linear motion. Unexpectedly, afte r adaptation, trunk and head perceived orientations were attracted tow ard the direction of the imposed motion. This suggests that the intern al representation of body configuration depends also upon available cu es from the extrapersonal space.