Intentional changes in sound pressure level and rate: Their impact on measures of respiration, phonation, and articulation

The purpose of the study was to compare the effects of changing sound pressure level (SPL) and rate on respiratory, phonatory, and articulatory behavior during sentence production. Ten subjects, 5 men and 5 women, repeated the sentence, 'I sell a sapapple again,' under 5 SPL and 5 rate conditions. From a multi-channel recording, measures were made of lung volume (LV), SPL, fundamental frequency (F₀), semitone standard deviation (STSD), and upper and lower lip displacements and peak velocities. Loud speech led to increases in LV initiation, LV termination, F₀, STSD, and articulatory displacements and peak velocities for both lips. Token-to-token variability in these articulatory measures generally decreased as SPL increased, whereas rate increases were associated with increased lip movement variability. LV excursion decreased as rate increased. F₀ for the men and STSD for both genders increased with rate. Lower lip displacements became smaller for faster speech. The interspeaker differences in velocity change as a function of rate contrasted with the more consistent velocity performance across speakers for changes in SPL. Because SPL and rate change are targeted in therapy for dysarthria, the present data suggest directions for future research with disordered speakers.