Visual discrimination between a curved and straight path of self motion: effects of forward speed.

We measured path-deviation thresholds for discrimination between forward movement along a straight and a curved path as forward speed was varied. Stimuli were computer-generated images simulating an observer moving relative to a volume of randomly-positioned dots. Predictions generated from a computer simulation of Rieger's [(1983) Journal of the Optical Society of America A, 73, 339-344] model indicate that the required deviation for the discrimination of a curved from straight path should decrease with increasing forward speed up to a point and then level off. Psychophysical results were opposite to the model predictions; the deviation required to detect a departure from a straight path increased with forward speed. Path curvature remained nearly constant across forward speeds for a constant level of discrimination performance.