Physiological bases of acoustic LRT in nonstutterers, mild stutterers, and severe stutterers.

The simple reaction time paradigm, incorporating a variable foreperiod, was used to investigate relative contributions of the respiratory and laryngeal systems to mild and severe stutterers' prolonged acoustic laryngeal reaction time (LRT) values. Prephonatory kinematic data were analyzed in terms of frequency of initiation, timing, and organization of events executed to attain the functional physiological targets of respiratory inflation during foreperiods and phonation onset after foreperiods. Acoustic data replicated a previously observed composite stuttering severity and foreperiod effect on stutterers' acoustic LRT values. Kinematic data revealed that, in general, the mild stutterers demonstrated delayed initiation of respiratory events and appropriate organization of respiratory and laryngeal events while the severe stutterers demonstrated delayed initiation of laryngeal events and inappropriate organization of respiratory and laryngeal events. That is, kinematic data both account for group differences in acoustic LRT values as a function of foreperiod and support the notion that differential respiratory and laryngeal deficits underly mild and severe stutterers' prolonged acoustic LRT values.