Similar working memory outcomes with successive versus concurrent presentation of tones and colors

Performance in a short-term or working memory task may depend on the ability to construct and retain a representation of multiple items fitting a single, coherent scheme. Judging by a theoretical tradition based on selective attention tasks, there might be encoding of perceived items into working memory limited to a single coherent stream of information at a time. However, this notion of a single stream seems to conflict with another tradition in which several items can be absorbed into working memory and retained at once. In three large-scale experiments (N ~ 120 per experiment), we examined working memory for series of colors and tones that were presented either successively, with all of one modality before the other, or concurrently, with one tone accompanying each color but uncorrelated with it. The single-stream account would suggest considerable difficulty for the concurrent presentation method. However, no such effect was obtained. There was no effect of the presentation method in the recognition of items (Experiments 1 and 2) and only a small modifying effect in memory for the serial position of items (Experiment 3). All experiments replicated earlier findings of a detrimental effect of having to retain two sets compared to one, and of an asymmetry in which the dual-set effect was larger for the visual modality. The extant evidence supports a theory in which multiple, separate episodic streams can be encoded into working memory concurrently, provided that the rate of information input does not exceed a rate of processing.