Testing a positional model of the Hebb effect

In two experiments, we investigate the hypothesis that a strengthening of position –item associations underlies the improvement seen in performance on an immediate serial recall task, when a given in list is surreptitiously repeated every third trial. Having established a strong effect of repetition, performance was tested on transfer lists in which half the items held the same position as in the repeated list (S-items), the remainder moved (D-items). In Experiment 1, S-items showed a small advantage over control and D-items, in order errors. A second experiment tested whether a design element in Experiment 1 underlay this advantage. When the experimental design was better controlled, no improvement was shown for either S- or D-items over controls. These data were shown to be inconsistent with the results of computer simulations of a positional model. An alternative model is outlined.