Time estimation of visually presented increment and decrement stimuli: the filled-duration illusion

Experiments were carried out to estimate the duration of time intervals in the 100-1100 ms range, using the direct scaling method. Time intervals were filled: (a) by increment visual stimuli on a light background, (b) by decrement visual stimuli on a light background, (c) only by background illumination. The results obtained show that increment stimuli are perceived as equal in duration to the decrement stimuli. Both increment and decrement stimuli are perceived to be longer than the intervals during which only the background was presented. These results make it possible to generalize the concept of filled and unfilled intervals. A hypothesis is raised that the filled-duration illusion is due not to the properties of the on- and off-effects in the visual system but to processes in the iconic memory connected with the presence of an image (increment or decrement) in the filled intervals.