Effects of reference lines on displacement thresholds at various durations of movement.

Displacement thresholds were determined for durations of movement between 10 msec and 2.5 sec, with and without the presence of a reference line. For all durations of movement, displacement thresholds were lower when a reference line was present. The magnitude of this effect was essentially constant across all durations of movement. These data suggest that previous reports of differential effects of reference lines on long and short durations of movement depend upon the stimulus paradigm employed.