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.