Spatio-temporal interactions in immediate serial recall

In an immediate serial recall task, participants are asked to recall lists of items in order. In the Hebb repeating-list variant of the task, subjects are read a series of lists, and every third list is repeated. Performance improves across repetitions but is stable for the non-repeated trials. The repetition advantage---the increased accuracy for the repeated list---is known as the Hebb effect. Several models have been advanced to explain how participants order successive items, but how participants take advantage of the repetition has largely been ignored. Although the task is usually discussed in terms of recall of verbal items, the Hebb effect has been observed with sequences of visuo-spatial positions.; The present work assesses whether immediate serial recall of verbal material benefits from visuo-spatial context. Sequences of letters were presented in different spatial positions in a visual version of the Hebb task. Presenting lists in random spatial positions on the periphery of an imaginary circle did not boost performance, but if the sequence was predictable, overall accuracy increased. The spatial path of successive items influenced the Hebb effect. When the distance between successive positions was minimized, participants were able to exploit the repetition early in practice. The results deny an account based on item distinctiveness. I discuss the results in terms of contemporary models of ISR.