Influence of fixation on circular vection.

The contribution of fixation to latency of circular vection (CV) was examined in twenty-five normal adults aged 18-30 years. For induction of self-motion a random dot pattern was projected onto a hemispherical dome. The pattern was rotated either about the subject's vertical axis or about their interaural axis at a constant acceleration of 1 deg/s2. For the group tested, the perceived CV latencies were significantly shorter with fixation than without fixation in both horizontal and vertical CV. The effect of fixation was pronounced in subjects with longer latencies. The mean CV latencies for two different fixation points between the subject's eyes and the moving pattern did not differ significantly. Our results suggest that the potential influence of fixation must be carefully controlled in studies of visually induced self-motion. Possible explanations for the effect of fixation on the generation of CV will also be discussed.