The stimulus prefix is not irrelevant and is redundant in different ways.

The present study examined the stimulus prefix effect of immediate recall under conditions in which the prefix element was defined explicitly as being an irrelevant item that should be ignored, or, alternatively, as an item to be remembered and recalled. Memory was poorer in the latter case. Also examined were the effects of three types of redundancy relation between the prefix and target elements; one of these, interstring redundancy (same prefix precedes each target string), was found to improve recall in a relative sense, and another, conceptual redundancy (prefix and target items belong to the same conceptual category), was found to degrade it. Thus, that part of the conventional stimulus prefix effect attributable to redundancy, per se, can be viewed as a composite of at least two opposing factors. Finally, the independent variables of the present study were interpreted to impose different information-processing requirements on the subject, and an account of these requirements was offered.