Just-noticeable difference in the speed of cyclopean motion in depth and the speed of cyclopean motion within a frontoparallel plane.

Weber fractions for discriminating the speed and displacement of a cyclopean target moving in depth ranged, respectively, from .07-.17 and .06-.13 over 6 observers. Corresponding data for a noncyclopean target were .07-.20 and .06-.12. For motion parallel to the frontal plane, corresponding data were .09-.20 .06-.16, and .05-.13. All Weber fractions were independent of the direction of motion and of near versus far disparity. All observers based their judgments entirely on the task-relevant variable and ignored task-irrelevant variables in all cases. We conclude that speed and displacement are encoded independently and in parallel for motion in depth and for motion within a frontoparallel plane.