Short-term memory demands of reaction-time tasks that differ in complexity.

Four experiments were conducted to determine whether the increased reaction time produced by loading memory with a set of irrelevant items depended on the complexity of the stage structure or of the stimulus-response (S-R) mapping rules underlying the task. In each experiment, reaction-time tasks varying in complexity were performed alone and in the retention interval of a short-term memory task requiring ordered recall of eight digits. Experiment 1 compared simple, choice, and go/no-go tasks over 3 days of practice and found no interaction between memory load and task complexity. Experiment 2 replicated the first day of Experiment 1 with more power and again found no interaction. Since the different tasks required different numbers of stages, this ruled out stage structure as a factor loading memory. However, in Experiment 1 and 2, the same subjects performed all three tasks with the same set of letters and may have developed one comprehensive set of mapping rules for all three tasks, essentially eliminating differences in memory demands between tasks. Experiment 3 used different groups of subjects