One hundred fifty years after Donders: Insights from unpublished data, a replication, and modeling of his reaction times.

Mental processes take a measurable amount of time, which was discovered by Donders one hundred fifty years ago. He reports process durations in his classic study with the a-, b-, and c-methods (i.e., simple, choice, go/no-go) using a speech repetition task. His reaction time pattern was a < c < b. He reasoned that the c - a difference gives the discrimination duration, and the b - c difference the choice duration. A few years later, Wundt criticized the c-method by arguing that it does involve a choice (i.e., whether or not to respond, which is an act of executive control), whereas Donders maintained that it may not involve full discrimination. The substance of this historical controversy relates closely to modern issues in the study of reaction times. Here, I show that an analysis of unpublished data from a handwritten laboratory notebook of Donders reveals no b - c difference for his students, supporting Wundt's concern. Moreover, a replication of Donders' study using his original stimulus lists yielded only a small b - c difference for myself, supporting Wundt. A computer simulation using a modern model of speech repetition indicates that the difference between Donders and his students may plausibly result from choice in the c-method. To conclude, unpublished data, a replication, and modern modeling resolve a 150-year-old issue, stressing the importance of examining individual differences and executive control in performance.