ELECTROPHYSIOLOGICAL EVIDENCE ON THE TIME-COURSE OF SEMANTIC AND PHONOLOGICAL PROCESSES IN SPEECH PRODUCTION

The temporal properties of semantic and phonological processes in spee ch production were investigated in a new experimental paradigm using m ovement-related brain potentials. The main experimental task was pictu re naming. In addition, a 2-choice reaction go/no-go procedure was inc luded, involving a semantic and a phonological categorization of the p icture name. Lateralized readiness potentials (LRPs) were derived to t est whether semantic and phonological information activated motor proc esses at separate moments in time. An LRP was only observed on no-go t rials when the semantic (not the phonological) decision determined the response hand. Varying the position of the critical phoneme in the pi cture name did not affect the onset of the LRP but rather influenced w hen the LRP began to differ on go and no-go trials and allowed the dur ation of phonological encoding of a word to be estimated. These result s provide electrophysiological evidence for early semantic activation and later phonological encoding.