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Chunking groups separate items into meaningful units for recognizing patterns or using short-term memory. Several digits can be treated as one familiar date, for example, so the same number of visible symbols can require different numbers of remembered units. The grouping draws on knowledge in long-term memory; inserting spaces alone does not make an unfamiliar pattern meaningful.

William G. Chase and Herbert A. Simon investigated these units by asking three chess players of differing skill to reconstruct positions and examining pauses and successive glances during reconstruction. The pattern of pieces placed together provided evidence about the structures a player perceived, rather than simply measuring the total number of pieces remembered.^[ref] Expertise can therefore improve performance by changing the representation of the material, without demonstrating an equal improvement in every unrelated short-term memory task.

Elizabeth Warrington studied human memory through selective patterns of preservation and impairment. With Tim Shallice, she investigated the patient published as K.F., whose auditory-verbal short-term memory was selectively impaired. Comparing that profile with other human memory measures constrains models of the relationship between temporary retention and longer-term learning, rather than reducing the case to one overall human memory score. ^[ref]