Temporal frequency of events rather than speed dilates perceived duration of moving objects

In everyday life moving objects often follow irregular or repetitive trajectories for which distinctive events are potentially noticeable. It is known that the perceived duration of moving objects is distorted, but whether the distortion is due to the temporal frequency of the events or to the speed of the objects remains unclear. Disentangling the contribution of these factors to perceived duration distortions is ecologically relevant: if perceived duration were dependent on speed, it should contract with the distance from the observer to the moving objects. Here, we asked observers to estimate the perceived duration of an object rotating at different speeds and radii and found that perceived duration dilated with temporal frequency of rotations, rather than speed (or perceived speed, which we also measured). We also found that the dilation was larger for two than for one object, but the increase was not large enough to make perceived duration independent of the number of objects when expressed as a function of the local frequency (the number of times an object crossed a given location per time unit). These results suggest that perceived duration of natural stimuli containing distinctive events doesn't depend on the distance of the events to the observer.