Perception of direction of visual motion. II. Influence of linear body acceleration

We investigated whether linear whole-body acceleration along the interaural y-axis influenced the concurrent perception of visual motion direction 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 they perceived visual motion to the left within a random-dot kinematogram continuously presented on a monitor moving with them. The percentage of coherently leftward moving pixels presented for a 640-ms period during acceleration was adjusted according to a Modified Binary Search (MOBS) procedure. Six conditions were tested, two acceleration levels of 1 and 2 m/s2 to both left and right with, at the higher acceleration, two different times of visual motion presentation. Conditions were sequenced by means of a 6 x 6 Latin square balanced for order and carry over. A MANOVA did not show any statistically significant effects either for the independent variables acceleration, velocity, and direction of motion of the sled or for their interactions. The results obtained are in clear contrast to those obtained under rotatory stimulation. We conclude that the otolithic contribution to vestibular-visual motion processing is negligible.