Temporal and spatial characteristics of the upper displacement limit for motion in random dots.

The upper displacement limit (Dmax) or Braddick limit was measured in random dots. We then interposed a variable duration pause at half the distance jumped. Of interest was to see the shortest time (delta t) which would yield a value of two times Dmax, thus indicating the time required to process one additional Braddick limit. A surprisingly short interval (as short as 10 msec under some conditions) was required. Furthermore for intermediate durations (20 to over 100 msec), the total limit was often more than doubled, indicating a nonlinear potentiation or sequential recruitment between successive displacements. Increasing field size had the following effects: (1) it increased Dmax, (2) it decreased delta t (the processing time), (3) it increased Vmax (the maximum velocity), (4) it increased the amount of sequential recruitment.