Rickard, T. & Pashler, H. (Technical Report). A Bottleneck in Memory Retrieval from a Single Cue. Center for Human Information Processing Technical Report 2005-01.
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We explored whether two memory retrievals from a single cue can be completed in parallel. Subjects were trained to make a vocal response and a key press response for each of a set of ten visually presented words. Subsequently, these two tasks were interleaved with a third, dual task condition in which subjects retrieved both the vocal and the key press response on each trial. Findings include: 1) the latency of the first retrieval on dual retrieval trials exceeded that of either of the two tasks performed by themselves, 2) the time to finish the dual retrieval task was roughly the sum of the time to finish the two tasks on separate trials, 3) the correlation between time to finish the first task (RT1) and the inter-response interval (IRI; latency between the first and the second response) was not significant, and 4) some subjects always choose to execute the slower task first on dual task trials. Taken together, these and other findings favor a sequential retrieval model over a broad class of parallel models.