Three interpretations of short-term verbal memory are discussed, one based on association theory, one on neutral computer modeling, and one on the mechanisms of speech perception, conceived as an active process. The prefix effect, in with a redundant stimulus (or response) digit acts like a non-redundant one in its load on memory, is easily explained by the speech-perception hypothesis but seems to pose difficulty for the other approaches. Two experimental conditions were devised which should eliminate the stimulus prefix effect if the postulated relationship with active speech perception is valid: (a) using a different speaker for the prefix; (b) using three identical digits as prefix rather than one. Two experiments were carried out, each testing both predictions. The expected pattern of results emerged in both studies. © 1969 Academic Press Inc. All rights reserved.