In this study, the authors examined whether a visual analog scale (VAS; as below, but with speech sounds) can be used to perceptually characterize speech variability within phonetic categories. A group of adults (not SLPs) listened to /s/ and /θ/ syllables extracted from words produced by 2–5-year-old children. Their task was to place the sounds on a continuum from /s/ vs. /θ/. The scale was found to be quite useful, in that its measures correlated “…with a variety of continuous measures of children’s production…”.
This study represents an initial step in a larger goal of identifying when and how visual analog scales could be used to accurately characterize speech. Would similar results be obtained for sounds other than /s/ vs. /θ/?
For SLPs, this could be a great option for charting clients’ progress, and the authors have research underway specifically looking at this. For our purposes, transcription sometimes isn’t enough to capture subtle changes in speech that occur during the course of therapy. We'll need to know whether SLP use of the scale produces the same results and lay people's use of the scale, how the scale works for other speech sounds, and whether the measure is reliable over the course of weeks or months.
See: Schellinger, S.K., Munson, B., & Edwards, J. (2016). Gradient perception of children's productions of /s/ and /θ/: a comparative study of rating methods. Clinical Linguistics and Phonetics. Advance online publication. doi: 10.1080/02699206.2016.1205665.