Typing Errors as Clues to Serial Ordering Mechanisms in Language Behaviour

623 typing errors produced by 5 subjects in a free typing situation were classified into two main categories : (a) spatial errors, in which a letter adjacent on the keyboard to the correct letter was typed, and (b) temporal errors, or errors in the order in which the required letters were typed. Spatial errors were mostly associated with the left hand and keyboard difficulty, while temporal errors mostly arose from language structure variables. Results were incompatible with “one stage” or “chaining” theories of serial ordering. They suggested a hierarchical or “three stage” output mechanism consisting of (a) a “determining tendency”, (b) a programming mechanism, reflected by temporal errors, and (c) a relatively separate executive mechanism, reflected by spatial errors. Some characteristics of the programming mechanism are discussed.