Partially selective search of memory for letters and digits

Three experiments failed to provide evidence that subjects could search just the digits, or just the letters, of a mixed list of digits and letters in deciding whether a probe item was a member of the list. Providing a precue as to the category of the probe shortly before the presentation of the probe decreased the time needed to encode it, but did not change the memory search process. Repeating the category of the probe from one trial to the next, however, did change the pattern of memory search. A "partially selective search" model was proposed which claimed that a mixed list was stored as two categorized sublists, and that a self-terminating search of the sublists could occur in which the first sublist searched was the one which had been probed on the previous trial.