Comparison of electrophysiological correlates of writing and speaking: a topographic ERP analysis

Behavioral and neuropsychological studies on written production suggested that some cognitive processes are common with spoken production. In this study, we attempted to specify the time course of common processes between the two modalities with event-related brain potentials (ERPs). High density EEG was recorded on twenty two healthy participants during a handwritten and an oral picture naming task on the same 120 stimuli. Waveform analyses and topographical pattern analyses were combined on stimulus- and response-aligned ERPs in order to cover the whole word encoding processing. Similar electrophysiological correlates between writing and speaking appeared until about 260 ms. According to previous estimations of the time course of spoken production, the time period of identical electrophysiological activity corresponds to visual (0-150 ms) semantic (150-190 ms) and lexical-semantic (190-275 ms) processes. Then, spoken and handwritten picture naming starts diverging and display different and modality specific topographical configurations from around 260 ms, i.e., at the beginning of the time-window associated to the encoding of the surface phonological form in spoken production. These results suggested shared conceptual and lexical-semantic processes between speaking and writing and different neurophysiological activity during word-form (phonological or orthographic) encoding.