DISCRIMINATION OF THE DIRECTION AND SPEED OF MOTION IN-DEPTH OF A MONOCULARLY VISIBLE TARGET FROM BINOCULAR INFORMATION ALONE

Thresholds for discriminating a monocularly visible object's direction of motion in depth and speed of motion in depth were measured using o nly binocular cues. Observers could discriminate the direction of moti on in depth while totally ignoring speed and discriminate the speed of motion in depth while totally ignoring direction. Direction discrimin ation thresholds were the same for motion in depth within the vertical and horizontal meridians, even though a cue to trajectory was availab le for motion within the horizontal meridian that is not available for motion within the vertical meridian. Speed discrimination thresholds also were the same for motion in depth within the vertical and horizon tal meridians. For the 3 observers the lowest direction discrimination thresholds were 0.14 degrees, 0.18 degrees, and 0.22 degrees (means o f horizontal and vertical thresholds).