Updated on December 7, 2008

The Spans Question

The spans question asks, What is the nature of the three span limits in human performance? Each span is an abrupt performance limitation with a curiously small value of about 7. These limits are shown in the figure below. Scientific interest in the spans question has gone in and out of style for over 100 years and was of considerable interest to philosophers before that. It is the main topic of the most famous paper in psychology, Miller (1956).

The limits are of scientific interest for several reasons. First, the limits are small and surprisingly resistant to improvement with practice so they challenge the notion of nearly unlimited human abilities. Second, the size of the limits bears a remarkably close relationship with intelligence and status as mentally retarded or non-retarded.

Despite the long history of research and thought, the nature of the limits is still very much in question. The current dominant point of view is that the three spans reflect distinct limitations in memory, attention, and psychophysical processes, respectively. This multiple-spans point of view contrasts with unitary points of view, such as span theory, which hold that the three limits are variations on a single underlying limitation.

The three span limits

This figure presents the three span limits. In each type of task "set size" is a potent experimental variable. When set size is small (toward the left in the figure) performance is almost perfect, trial after trial. As set size increases to about 5, errors start to occur. As shown on the figure, after set size 9 it is rare to see a fully correct response.


Guilford, J. P., & Dallenbach, K. M. (1925). The determination of memory span by the method of constant stimuli. American Journal of Psychology, 36, 621-628.

Mandler, G., & Shebo, B. J. (1982). Subitizing: An analysis of its component processes. Journal of Experimental Psychology: General. 111, 1-22.

Miller, G. A. (1956). The magical number seven, plus or minus two: Some limits on our capacity for processing information. The Psychological Review, 63, 81-97.

Pollack, I. (1952). The information of elementary auditory displays. The Journal of the Acoustical Society of America. 24, 745-749.