Modulation of auditory processing during speech movement planning

Ludo Max, Dept. of Speech and Hearing Sciences, Dept. of Linguistics, and Dept. of Bioengineering, University of Washington, Seattle, WA

This talk will include an overview of a series of electroencephalographic (EEG) studies investigating modulation of the auditory system during the planning phase immediately prior to speech onset. All studies included typical speakers; some studies also included stuttering speakers. Study I was a methodological study in which we developed the basic paradigm. In this paradigm, long-latency auditory evoked potentials (LLAEPs) are recorded in response to probe tones presented during speech movement planning in a speaking condition and during non-speaking control conditions. Typical adults showed a significant modulation of the N1 component in the LLAEP when preparing to speak as compared with reading the same words silently. Study II replicated this finding for typical speakers but found a lack of modulation for stuttering speakers. Study III investigated in typical speakers the effect of using tones vs. truncated syllables as the probe stimuli. Results indicated that the auditory N1 component is modulated equally for tones and syllables, but a subsequent modulation for the P2 component was observed only with syllable stimuli. Study IV investigated the functional relevance of pre-speech auditory modulation, and again included both typical and stuttering speakers. Stuttering individuals’ lack of pre-speech auditory modulation did not account for their also limited auditory-motor learning, but normalized when speaking with delayed auditory feedback. Lastly, Study V demonstrated that the same modulation phenomenon can also be observed in a picture naming task developed for use with children. Overall, the results from this series of studies provide new insights into processes underlying sensorimotor interactions during speech motor planning.