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Two experiments are reported in which subjects performed two forced-paced serial reaction time tasks separately and together at their maximum sustainable rates of information processing. Experiment 1 investigated the effects on the relationship between single- and dual-task performance of using tasks with the same or different input and output modality characteristics; an additional condition tested the effects on this relationship of using tasks with higher S–R compatibility. Experiment 2 investigated the effects on the relationship between single- and dual-task performance of varying information load (number of S–R alternatives). No significant differences were found in subjects’ capacities to process information in single- and dual-task conditions. This finding was unaffected by: (a) the absolute information levels of the tasks, (b) whether inputs and/or outputs involved the same or different modalities, or (c) the level of S–R compatibility. The data from both experiments provide strong support for the single-channel hypothesis.
Gladstones et al. (Wed,) studied this question.