Random generation and the executive control of working memory

A series of experiments explores the capacity for generating sequences of random responses, relating it to the central executive component of working memory. Experiment 1 shows a broadly similar pattern of redundancy increasing with speed of generation for both the verbal generation of digits and the manual pressing of keys. In both cases deviations from randomness are shown to reflect the increasing use of a limited number of stereotyped response sets. The remaining experiments use keyboard generation. Experiment 2 demonstrates that concurrent immediate serial recall decreases randomness, and that longer recall sequences produce less random output. Experiments 3 and 4 show that whereas simple counting has no effect on randomness, serial recall, semantic category generation, and concurrent digit generation have substantial effects, and a concurrent fluid intelligence test has the greatest influence on the randomness of key pressing. It is suggested that the task of random generation resembles that of category fluency because it requires the subject to switch retrieval plans and inhibit repetition. On this basis it is predicted that a task involving repeated switching of categories will interfere with generation, despite being predictable and having a low memory load. Experiments 5 and 6 confirm this prediction. Strengths and limitations of the switching hypothesis are discussed, as are the implications of our results for the analysis of executive processes.