We present here a general theory of human reaction time (RT) that covers the three kinds of RT experiments originally described by Donders. The theory is not a stage model as originally envisioned by Donders and his successors. Rather, the strength of the excitatory tendency leading to response evocation grows continuously as a function of the time since stimulus onset. Response occurs when this strength reaches the value of a decision criterion that is normally distributed over trials. This leads to a Thurstonean measurement model that facilitates the analysis of data and has led to the development of the present theory.Excitatory strength may consist of either one or two processes: detection information, dependent on sensory strength, and associative strength. In simple RT only detection is involved, but in choice RT both are present. The analysis further reveals that in disjunctive RT, the Donders c reaction, there are two modes of performance, or "strategies," used by different subjects. Thus, correct performance may depend on the detection process alone or on the associative process as well. The theory also deals with the dynamics of making and avoiding errors and, consequently, with the speed-accuracy tradeoff. Associative inhibition attenuates incorrect tendencies resulting from detection, and associative discrimination attenuates generalized associative strength for the incorrect response. Both processes grow with time.In this article the theory is applied to a series of five experiments with auditory stimuli differing in intensity. Intensity was the basis of differential response in disjunctive and choice experiments. The theory successfully describes the data of the individual subjects in all experiments as well as the group data. Subjects apparently adjusted their criteria between experiments in disjunctive RT and between responses in choice RT as a means of reducing short latency errors to the more intense stimulus.The theory provides an analysis of the nature of individual differences, which also reveals further features of information-processing dynamics. An important one of these is the role of criterion variability in causing errors.
