PERCEPTION OF DIRECTION OF VISUAL-MOTION .2. INFLUENCE OF LINEAR BODYACCELERATION

We investigated whether linear whole-body acceleration along the inter aural y-axis influenced the concurrent perception of visual motion dir ection as has been shown for angular accelerations. A sled running on air bearings along a 7.5-m track was used to accelerate 18 subjects at two different linear accelerations. These young, healthy volunteers, aged 25.50+/-7.38 years, used a joystick to indicate whether or not th ey perceived visual motion to the left within a random-dot kinematogra m continuously presented on a monitor moving with them. The percentage of coherently leftward moving pixels presented for a 640-ms period du ring acceleration was adjusted according to a Modified Binary Search ( MOBS) procedure. Six conditions were tested, two acceleration levels o f 1 and 2 m/s(2) to both left and right with, at the higher accelerati on, two different times of visual motion presentation. Conditions were sequenced by means of a 6 x 6 Latin square balanced for order and car ry over. A MANOVA did not show any statistically significant effects e ither for the independent variables acceleration, velocity, and direct ion of motion of the sled or for their interactions. The results obtai ned are in clear contrast to those obtained under rotatory stimulation . We conclude that the otolithic contribution to vestibular-visual mot ion processing is negligible.