On distinguishing human behavior by means of mutual interference

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Humans show enormous varieties of behavior: They range from simple, unavoidable reflexes (i.e., non-intentional behavior) to actions, that is, behavior that is shown with a particular intention to achieve a certain goal. In the latter case, psychologists sometimes distinguish externally-triggered and internally-initiated actions. These are operationalized most often with so-called forced-choice tasks (where a stimulus determines the one and only correct action) and free-choice tasks (where the actor can choose among several equally correct actions), respectively. The empirical evidence for this distinction, however, is unclear.In the first project-phase the susceptibility to dual-task interference was taken to investigate qualitative distinctions between such types of behavior. The results allow the following conclusions: (1) Non-intentional behavior is not susceptible to dual-task interference and thus differs qualitatively from (interference-susceptible) actions. (2) Both (sometimes distinguished) types of actions are equally susceptible to dual-task interference and thus do not differ qualitatively. The focus of the present second project-phase is the conceptualization of forced-and free-choice tasks within one framework, which is inspired by sequential sampling models. Pilot experiments suggest that in both types of tasks evidence accumulates, and even with the same rate. However, both tasks differ in their non-accumulation times. This framework will be tested further in several experiments, in particular to test whether a secondary dual-task affects the same components of both tasks. Additionally, the function of the additional non-accumulation time in free-choice tasks (and thus the basis of accumulation) and the effects of various kinds of intentions are investigated.The results of this project-phase will (1) help to clarify the relation of forced- and free-choice tasks, and (2) provide the basis for a subsequent formal modelling of the projects results and the literature on both task-types.