The "jump" effect

The jump effect occurs when an object, for example, a small square, moves on a homogeneous background at a constant velocity along its path except for a short section wherein the velocity suddenly changes to a higher value. In correspondence with this increase, observers may report that the object appears to jump. The experiments reported here explored the velocity conditions which determine the occurrence of this perceptual jump. A difference of at least 15 cm/sec. between the two velocities of the object was necessary for the effect to occur with probability 0.5. With slightly lower frequency, the effect also occurred when the object increased its velocity to a higher constant value in a short part of its path and then stopped. For the phenomenal jump to occur in all the different conditions used, there had to be an optimal length of the path in which the object increased its velocity. Finally, both velocities, before and after this increase, influenced the jump, although each with different weight.