Reproduction of ON-center and OFF-center self-rotations.

In self-rotation reproduction tasks, subjects appear to estimate the displacement angle and then reproduce this angle without necessarily replicating the entire temporal velocity profile. In contrast, subjects appear to reproduce the entire temporal velocity profile during linear motion stimulating the otoliths. To investigate what happens during combined rotation and translation, we investigated in darkness the central processing of vestibular cues during eccentric rotation. Controlling a centrifuge with a joystick, nine healthy subjects were asked to reproduce the angle of the previously imposed rotation. Rotations were either ON-center, or 50 cm OFF-center with inter-aural centripetal acceleration. Rotation duration was either variable (proportional to the traveled angle), or constant. We examined whether the stimulation of the otoliths during OFF-center rotation changes self-rotation reproduction, and whether rotation duration is processed differently by the nervous system with and without otolith stimulation. As postulated, the subjects indeed reproduced more closely the stimulus velocity profile when OFF-center. But the primary result is that the additional supra-threshold linear acceleration cues, measured by the otoliths, did not improve performance. More specifically, to our surprise, the ability to reproduce rotation angle degraded slightly in the presence of additional information from the otolith organs, with the linear acceleration cues appearing to interfere with the reproduction of movement duration.