Filled-Duration Illusions

Abstract

Abstract Data relevant to the ‘filled-duration illusion’, the claim that filled intervals appear to last longer than unfilled ones of the same real duration, are reviewed. A distinction is made between divided-time studies (where an empty interval has one or more than one brief dividing stimulus inside it) and filled-duration studies (where the filled intervals are filled with some continuous event). Divided durations appear to last longer than empty ones, and the effect grows with the number of dividers, although it may be restricted to short durations. The best current explanation appears to involve the weighted summation of the different subintervals of which the total duration is composed. When intervals with simple fillers are contrasted with empty ones, they are usually judged as longer, and the effect may grow as the intervals lengthen, at least over short duration ranges. When complex fillers are used, fillers usually have no effect on perceived duration or shorten it. A pacemaker-counter approach can account for some simple filler effects, and division of attention for complex filler effects. Although there are some exceptions, ‘filled-interval illusions’ of all these types are normally found, but some problems, such as questions about the relative perceived variability of filled and unfilled intervals, or stimulus order effects, merit further research.