On the interaction of concurrent verbal and manual tasks: which initial task conditions produce interference?

The presence of interference (and whether it is generalized or lateralized) is highly dependent on the initial conditions of the experiment. Changes in task, instructions, and subject characteristics produce different interference outcomes. Clearly the present results are not predictable from the cerebral functional distance theory and support the idea that the theory has limited explanatory power depending on the specific tasks and conditions involved. Alternatively, the idea of entrainment among tasks can account for some of the results, particularly for the preferred-speed conditions. In other words, the interference may be interpreted in terms of a task integration of two motor responses into a common rate rather than in terms of structural interference effects (cf., Murphy & Peters, 1994). From this viewpoint, it would appear that much more could be gained by systematically changing the test conditions (task constraints) to determine the different sources of interference and/or by testing specific populations (e.g., Bathurst & Kee, 1994). In the meantime, if an experimenter is specifically looking for lateralized interference in a dual-task paradigm it might be better either not to choose unimanual tapping or to avoid the motor task of finger tapping altogether so that attentional capacity is not confounded by the effects of nonattentional, mutually interacting outcomes. In general, the results of this study reflect the sentiment of Abernathy (1988), who suggests that the application of the dual-task paradigm to problems in motor skills research requires careful consideration of the available constraints operating in specific conditions.