a method of separating out hypothetical stages of mental processing by requiring participants to perform a set of reaction time tasks in which each successive task differs from its predecessor by the addition of a single mental stage. The time required to complete a particular stage of processing can be inferred by subtracting from the reaction time in one task the reaction time in the preceding task. For example, Task A, in which a person responds to one signal by pressing one key and to another by pressing another key, adds a response-decision stage to Task B, in which a person responds to one signal by pressing a key and makes no response to the other signal. Also called subtraction method. See also chronometric analysis; choice reaction time. [Franciscus Cornelis Donders]