Thresholds for detection of motion direction during passive lateral whole-body acceleration in normal subjects and patients with bilateral loss of labyrinthine function.

To investigate the effect of velocity, acceleration, and gradient of acceleration on self-motion perception, thresholds for detection of direction of whole-body interaural acceleration were determined for various stimulus profiles. For acceleration steps, acceleration thresholds at 67% correct detection of motion direction were similar for eight normals (mean 4.84 cm/s2 (range 2.9-6.3), peak gradient = 22 cm/s2) and five labyrinthine-defective subjects (mean 5.65 cm/s2 (4.85-6.6), peak gradient = 25 cm/s2). Velocity thresholds were 7.93 cm/s for a proportion of correct responses of 73% for normals and 9.67 cm/s for 69% of correct detection for avestibular subjects. For linear and parabolic accelerations, high intersubject variability was observed both among nine normals and three labyrinthine-defective subjects. Mean normal and avestibular subjects' acceleration thresholds for 74% of correct responses were respectively 12.1 cm/s2 (7.3-20.4) and 16.4 cm/s2 (13.2-20) for a ramp with gradient of acceleration = 2.8 cm/s3, 19.2 cm/ s2 (10.4-35.3) and 28.2 cm/s2 (21.4-32.8) for a ramp with gradient = 7.9 cm/s3 and 16.7 cm/s2 (10.5-25) and 20.6 cm/s2 (18.4-24.2) for a parabola with second derivative = 1.52 cm/s4. The corresponding velocity thresholds for normals were 21.2 cm/s (5.2-50.3), 22.0 cm/s (7-56.6), and 22.2 cm/s (9.5-43.7). The lowest thresholds were obtained for acceleration steps indicating that a high acceleration gradient facilitates motion perception. For linear and parabolic accelerations, motion perception seemed to follow an integration of acceleration, but a high intersubject variability was observed. For all stimuli, the range of thresholds for normals and avestibular subjects overlapped showing that detection of motion was not a sole prerogative of the otoliths but could also be performed using somatosensory cues.