Category-order effects in memory span

When Ss are required to recall lists containing both words and digits, memory span is higher when the digits precede the words than when the words precede the digits. In Experiment 1, both forward and backward recall were tested; it was demonstrated that this category-order effect reflects the input position, and not the output position, of the items. Experiment 2 revealed that this effect was not eliminated by a filled retention interval. Experiment 3 showed that the effect was eliminated when lists were presented at a fast presentation rate. In Experiment 4, the effect was eliminated when Ss engaged in articulatory suppression. A 5th experiment extended the findings of Experiment 4 to the case in which lists are composed of semantically related or unrelated words. These results suggest that category-order effects reflect mnemonic activity that Ss engage in during list presentation and do not arise from structural characteristics of the memory system.