ABSTRACT
This chapter sets out with a consideration of competition and interactions as potential sources of dual-task performance decrements. It focuses on interactions rather than competition. Mandatory interactions are distinguished from strategic ones and some speculations on their raison are offered. Various phenomena are reviewed that can be observed in the performance of simultaneous movements. Strategic interdependencies are an important problem in motor coordination, but they appear to be of less importance for dual-task performance than mandatory interactions which set the limits for what we can do. It is noteworthy that this preferred phase relation is the one that we use in walking, and it provides an example for the general hypothesis outlined above that the mandatory interactions between simultaneous movements are at least partially due to our phylo-genetic endowment with basic motor patterns.
