To determine whether there is a general capacity for all working memory tasks, Turner and Engle (1989) developed a task called operation-word-spanor OSPAN. In this task, participants are asked to read and verify a simple math problem (such as "Is (4/2)-1=1 ?) and then read a word after the operation (such as SNOW). After a series of problems and words has been presented, the participants recall the words that followed each operation. The number of operation-word strings in a sequence is increased and decreased to measure the participant's operation span. Operation span measures predict verbal abilities and reading comprehension even though the subjects are solving mathematical problems. Engle and his colleagues have argued that this implies a general pool of resources that is used in every type of working memory situation.
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