Attention, rehearsal, and memory for serial order.

In three experiments, subjects attended to one of two simultaneous nine-digit sequences, presented binaurally in different voices (one male, one female). Substantial repetition effects (defined as gains in immediate memory performance for previously presented sequences relative to novel ones) were found for two exposure conditions: (a) one that required reproduction of the full sequence on each exposure (Experiment 1), and (b) one that required recall of a different two-digit subsequence on each exposure (Experiment 2). In Experiment 3, the following conditions produced no repetition effects, even though tests had substantial power to detect small effects: 10 consecutive presentations in the unattended voice; 4 prior presentations in a task that required attention to each digit as it was presented (but not to digit order); and 4 prior presentations in a task that required attention to digit order during their presentations. These results, together with those of previous studies, support the conclusion that repetition effects on immediate memory occur only with procedures that encourage covert rehearsal of full-sequence order on each exposure. These findings also limit the generality of others' conclusions that event order is automatically encoded for attended events, and extend previous findings showing unattended exposures to be without effect on recall measures.