[Response force in probe reaction time tasks: reduction in capacity, response inhibition or bottle neck?]

The probe reaction time (probe-RT) paradigm suggested by Posner and Boies (1971) requires subjects to perform simultaneously a choice reaction task with two fingers of one hand (primary task) and a simple reaction task to randomly presented probes with the other hand (secondary task). The classical interpretation, according to which the RT of the secondary task indexes the capacity demands of the primary task, has been challenged, however. Active inhibition of the response and delay by a central bottleneck have been suggested as alternatives to the capacity account. The present study measured response force in addition to RT to distinguish among the three alternatives. Responses to the probe were clearly more forceful when the probe was presented while the subjects were engaged in the primary task. This result is most compatible with the active inhibition account by Neumann (1987, 1992) combined with an extended motor-readiness model.