Perception of plane orientation from self-generated and passively observed optic flow.

We investigated the perception of three-dimensional plane orientation--focusing on the perception of tilt--from optic flow generated by the observer's active movement around a simulated stationary object, and compared the performance to that of an immobile observer receiving a replay of the same optic flow. We found that perception of plane orientation is more precise in the active than in the immobile case. In particular, in the case of the immobile observer, the presence of shear in optic flow drastically diminishes the precision of tilt perception, whereas in the active observer, this decrease in performance is greatly reduced. The difference between active and immobile observers appears to be due to random rather than systematic errors. Furthermore, perceived slant is better correlated with simulated slant in the active observer. We conclude with a discussion of various theoretical explanations for our results.