The serial order of response units in word production: the case of typing

The selection and ordering of response units (phonemes, letters, keystrokes) represents a transversal issue across different modalities of language production. Here, the issue of serial order was investigated with respect to typewriting. Following seminal investigations in the spoken modality, we conducted an experiment where participants typed as many times as possible a pair of words during a fixed time-window. The 2 words shared either their first 2 keystrokes, the last 2 ones, all the keystrokes, or were unrelated. Fine-grained performance measures were recorded at the level of individual keystrokes. In contrast with previous results from the spoken modality, we observed an overall facilitation for words sharing the initial keystrokes. In addition, the initial overlap briefly delayed the execution of the following keystroke. The results are discussed with reference to different theoretical perspectives on serial order, with a particular attention to the competing accounts offered by position coding models and chaining models. Our findings point to potential major differences between the speaking and typing modalities in terms of interactive activation between lexical and response units processing levels.