Semantically Based Lexical Processing Yields Unique Topographic Contributions to the Speech Bereitschaftspotential

The Bereitschaftspotential (BP) is an event related potential believed to reflect motor planning and preparedness. Although the relationship between the BP and volitional movements of the distal limbs is well established, studies of the BP and speech have produced inconclusive findings. The most heavily debated of these findings were reports of left lateralized hemispheric asymmetry in the BP topography, shortly before speech onset. Several researchers argued that these shifts were artifacts produced by movements of the articulatory muscles. However, methodological differences between the studies could also explain why the asymmetry was not always found. In the present study it was proposed that articulatory complexity and semantic processing each contribute to observed variations in the speech BP topography. Eighteen healthy volunteers performed 3 speech tasks, designed to distinguish semantic and articulatory contributions to the BP topography. The findings suggested that articulatory complexity and semantic processing each uniquely contribute to the frontolateral and medial BP topographic distribution. The present study also introduced the use of Doppler imaging of the tongue as a means of eliminating potential artifactual tongue movements from the speech BP.