THRESHOLDS FOR PERCEPTION OF LATERAL MOTION IN NORMAL SUBJECTS AND PATIENTS WITH BILATERAL LOSS OF VESTIBULAR FUNCTION

Thresholds for detection of direction of whole-body lateral linear acc eleration were determined for normal (N) and labyrinthine defective (L D) subjects. Thresholds for 67% correct detection of direction of acce leration steps for 5 LDs (mean 5.65 cm/s(2), peak gradient = 25 cm/s(3 )) were not significantly different from 8 Ns (mean 4.84 cm/s(2), peak gradient = 22 cm/s(3)). High inter-subject variability was found both among the 7 Ns and 3 LDs for detection of parabolic accelerations wit h some individuals being unable to detect their motion direction. Mean Ns thresholds were 15.2 cm/s(2) for a ramp with gradient of accelerat ion = 2.8 cm/s(3), 26.4 cm/s(2) for a ramp with gradient = 7.9 cm/s(3) and 20.2 cm/s(2) for a parabola with second derivative = 1.52 cm/s(4) . Thresholds for LDs were respectively 19.1 cm/s(2), 32 cm/s(2) and 26 .7 cm/s(2). The lower thresholds for acceleration steps demonstrate th e important effect of acceleration gradient on motion detection. For a ll stimuli, thresholds for some LDs could be in the range of Ns showin g that somatosensory signals can play a significant role in detecting lateral acceleration.