THE LIST-STRENGTH EFFECT - STRENGTH-DEPENDENT COMPETITION OR SUPPRESSION

If several items are associated with a common cue, the cued recall of an item is often supposed to decrease as a function of the increase in strength of its competitors' associations with the cue. Evidence for such a list-strength effect has been found in prior research, but this effect could have been caused both by the strength manipulations and by retrieval-based suppression, because the strengthening and the outp ut order of the items were confounded. The experiment reported here em ployed categorizable item lists; some categories in each List containe d strong items only, some contained weak items only, and some containe d both strong and weak items. Strengthening was accomplished by varyin g the exposure time of the items. The testing sequence of the items fr om each category was controlled by the use of category-plus-first-lett er cues. When the typical confounding of strengthening and output orde r was mimicked, list-strength effects were found, which is consistent with prior research. However, when this confounding was eliminated, th e list-strength effects disappeared: The recall of neither strong nor weak items varied with the strengths of the other category exemplars. This pattern of results indicates that the list-strength effect is not the result of strength-dependent competition, but is caused by output -order biases and a process of suppression.