Peripheral @displacement thresholds (Dmin)[subscript] were measured in three young normal subjects in order to further our understanding of normal motion perception. The data will also be used in determining optimal stimulus parameters for clinical use, particularly the detection of early glaucomatous optic nerve damage. Random dot motion stimuli were generated on a high resolution Macintosh II computer. Bright dots were randomly positioned across a dark screen. Coherent motion was restricted to a square patch of variable size which, on a cue, underwent four sequential displacements separated by 150 ms. Displacement occurred in one of the four cardinal directions while the surrounding dots remained stationary. Subjects reported the direction of motion and a 4- AFC staircase procedure determined thresholds for a wide range of stimulus areas. Thresholds were determined for eccentricities of 0, 5, 10, and 15 degrees at viewing distances of 600 cm, 150 cm, 90 cm, and 60 cm, respectively. For foveal testing, the patch was in the center of the monitor, while for peripheral thresholds, a small fixation light was positioned adjacent to the monitor. As previously reported, our results show an increase in Dmin with retinal eccentricity. At a given eccentricity Dmin[subscript] shows a monotonic decrease with increasing stimulus area up to the critical summation area. For larger stimuli, little change occurs in Dmin[subscript]. For optimal stimulus conditions, Dmin[subscript] varies less with eccentricity than previously reported. Indeed, thresholds at 15 deg eccentricity were only twice that for foveal viewing. This can be contrasted with grating and letter acuity which increase by a factor of 7 and 16, respectively. We propose that the optimal stimulus area for a clinical test of motion perception should be equal to the critical summation area. Too large a patch will produce redundancy and too small a patch will limit the dynamic range.