Speech Elicitation Methods for Measuring Articulatory Control.

Purpose: Spatiotemporal index (STI) is a common measure of articulatory variability used to examine speech-motor control. However, the methods used to elicit productions for measuring STI have varied across studies. The aim of this study was to determine whether STI values are affected by changes in elicitation methods.
Method: Lip aperture STI (LA STI) was calculated for 19 monolingual English-speaking young adults based upon the production of four declarative sentences that varied by length and complexity. Using a 2 × 2 design, productions were elicited under the following two conditions: repetition type (consecutive vs. pseudorandom) and stimulus presentation type (auditory vs. combined auditory and visual). Conditions for eliciting productions were counterbalanced among participants.
Results: There was a main effect of repetition type ( p < .001) and sentence type ( p < .030). Pseudorandom repetitions resulted in higher mean LA STI values across sentence types compared to those computed from consecutive repetitions. There were no significant differences for stimulus presentation type. That is, no differences in mean LA STI were found between the auditory versus combined auditory and visual presentations.
Conclusions: Our findings show that the methods used to elicit sentence productions have a significant effect on LA STI values. Findings suggest that there is a need for researchers to consider these effects when designing methods for measuring LA STI.