Visual inertia in apparent motion

Four dots in an imaginary diamond were flashed in succession to give ambiguous apparent motion (AM). The top and bottom dots were flashed at time t1 and replaced by the left and right dots at time t2. If two priming dots were flashed beforehand at time t0 in line with two parallel sides of the diamond, AM was seen along those sides. We call this "visual inertia". The amount of visual inertia (measured by a null method) fell off with increasing angle between the priming dot and the side of the diamond. Visual inertia was still seen when the priming dots were presented to one eye and the test dots to the other, so the effect must be partly central. The timing and length of the priming path made little difference to visual inertia. However, static priming dots were ineffective. We conclude that the visual system was examining at least three successive time frames in deciding which items in one frame correspond with which items in succeeding frames.