Human visual navigation in the presence of 3-D rotations.

We report on the ability of human observers in judging their direction of translation from sparse, moving random dot patterns for varying extents of 3--D rotation. The observers have to discriminate possible axes of translation with angular separations of 2.5 deg or 5 deg. The field of view is either 20 X 20 deg or 10 X 10 deg. The simulated observer movement is relative to two types of scenes. The first type consists of dots located on a single plane at a depth Z. The second type of scenes consists of dots located on two transparent planes at different depths Z and Z + dZ. Unlike in the single plane condition, where the judgements about the direction of translation deteriorate quickly as the magnitude of 3--D rotation increases, we find for movements relative to planes at different distances a stable performance over a range of rotational magnitudes. Moreover we find that a reduction of the field of view from 20 X 20 deg to 10 X 10 deg does not affect the judgements significantly.