The intricacy of memory span.

The effects of word frequency on memory span were explored using the "up-and-down" method. Mean spans were greatest when the sequences were of all high-frequency words (5.82), and smallest when they were of all low-frequency words (4.24). For mixed-frequency sequences, mean spans were greater when the high-frequency words were presented before the low-frequency words (5.19) than when the low-frequency words came first (4.65). The findings are discussed in terms of the primary-secondary memory distinction worked out for single-trial free recall, and the logic of this distinction is used to argue against attributing span performance to a simple unitary process.