LIP-MUSCLE REFLEXES DURING SPEECH MOVEMENT PREPARATION IN STUTTERERS

Neural processes underlying speech initiation may involve reduction in the excitability of sensory input from mechanoreceptors that mediate speech movements. It is suggested that this reduced excitability is no t as great in individuals who stutter. The present experiment was inte nded to test this hypothesis by analyzing lip-muscle reflexes prior to speech initiation in stutterers and comparing these data to those obt ained in an earlier study with nonstutterers (McClean & Clay, 1994), M echanically evoked reflexes were studied in 14 adult stutterers prior to production of monosyllabic words beginning with the consonant p, Th e first component of the lip-muscle reflexes (R1) was quantified in te rms of percent modulation of mean response levels of upper- and lower- lip EMG relative to reflexes elicited during no-response trials. In th e previous study, 11 of IS nonstutterers showed significant attenuatio n of R1 across the upper and lower lip recording sites. In contrast, s ignificant R1 attenuation was observed in only 4 of 14 stutterers test ed here. As a group, stutterers showed less R1 attenuation prior to fl uent speech at the lower-lip recording site compared to the nonstutter ers. Reflex modulation associated with disfluent speech was quantified in three stutterers. Two showed marked increases in relative magnitud e of R1 prior to disfluent compared to fluent speech trials, Based on these various results, it is suggested that reduced attenuation of mec hanoreceptor input at the time of speech-movement initiation contribut es to speech disfluency.