Postcoincidence trajectory duration affects motion event perception.

In a two-dimensional display, identical visual targets moving toward and across each other with equal, constant speed can be perceived either to reverse their motion directions at the coincidence point (bouncing percept) or to stream through one another (streaming percept). Although there is a strong tendency to perceive the streaming percept, various factors have been reported to induce the bouncing percept, such as a sound or a visual flash at the moment of the visual target coincidence. By changing duration of the postcoincidence trajectory (PCT), we investigated how long it would take for such bounce-inducing factors to be maximally effective after the visual coincidence. With bounce-inducing factors, the percentage of the bouncing percept did not reach its maximal level immediately after the coincidence but increased as a function of PCT duration up to 150-200 msec. The results clearly reject the possibility of the cognitive-bias hypothesis about the bounce-inducing effect and suggest rather that the bounce-inducing factors have to interact with the PCT for some period after the coincidence to be maximally effective.