Acoustic and perceptual evaluation of category goodness of /t/ and /k/ in typical and misarticulated children's speech

Abstract

This investigation explores perceptual and acoustic characteristics of children's successful and unsuccessful productions of /t/ and /k/, with a specific aim of exploring perceptual sensitivity to phonetic detail, and the extent to which this sensitivity is reflected in the acoustic domain. Recordings were collected from 4- to 8-year-old children with a speech sound disorder (SSD) who misarticulated one of the target plosives, and compared to productions recorded from peers with typical speech development (TD). Perceptual responses were registered with regards to a visual-analog scale, ranging from "clear [t]" to "clear [k]." Statistical models of prototypical productions were built, based on spectral moments and discrete cosine transform features, and used in the scoring of SSD productions. In the perceptual evaluation, "clear substitutions" were rated as less prototypical than correct productions. Moreover, target-appropriate productions of /t/ and /k/ produced by children with SSD were rated as less prototypical than those produced by TD peers. The acoustical modeling could to a large extent discriminate between the gross categories /t/ and /k/, and scored the SSD utterances on a continuous scale that was largely consistent with the category of production. However, none of the methods exhibited the same sensitivity to phonetic detail as the human listeners.

Bias in the perception of phonetic detail in children’s speech: A comparison of categorical and continuous rating scales

“…This was true despite the fact that only productions transcribed to be correct were examined. Similar findings are reported by Strombergsson et al (2015), who showed that the /t/ productions of children with speech sound disorders are perceived as less /t/-like than those of their peers with typical speech development, even though these children’s /t/ productions were transcribed as accurate. Thus, a growing body of research suggests that continuous rating scales provide results that are reliable and may yield additional information about children’s productions that is similar to what can be gleaned from acoustic analysis.…”

“…Our speculation about how listeners might perceive the productions analyzed by Macken and Bartonis based on the results of numerous studies that elicit continuous ratings of children’s productions of sounds (Julien & Munson, 2012; McAllister Byun, Halpin, & Harel, 2015; Munson & Brinkman, 2004; Munson, Johnson, & Edwards, 2012; Munson, Schellinger, Edwards, Beckman, & Meyer, 2010; Strömbergsson, Savli, & House, 2015). These studies have shown that listeners are capable of providing continuous ratings of children’s productions, provided that the productions themselves vary continuously in how closely they resemble canonical productions of sounds.…”

Electropalatographic (EPG) evidence of covert contrasts in disordered speech

“…However, instrumental techniques such as EPG will remain an important source of information about the articulatory features that might underlie such differences. Strömbergsson et al's (2015) finding that 'correct' productions from the speech of children with disorders are less prototypical than those of typically developing peers can be considered analogous to the phenomenon of covert contrasts. Abnormal productions heard by listeners as correct are more accurately described as subtle articulatory errors and Cleland et al (this issue) refer to these articulations as 'covert errors'.…”

“…However, recent research reported in Munson, Edwards, Schellinger, Beckman and Meyer (2010), Munson, Schellinger and Urberg-Carlson (2012) and Strömbergsson, Salvi and House (2015) provide new evidence that covert contrasts are widespread in child speech. In these experiments, instead of restricting listeners to a categorical choice of selecting a transcription symbol, they used a continuous visual analogue scale to measure listener judgements about children's productions in terms of 'targetlikeness' or 'prototypicality'.…”

“…Collectively, these authors have concluded that listeners demonstrated high sensitivity to fine phonetic detail when making judgements that allowed for continuous rather than categorical judgements. The methodology adopted by Munson et al (2010) and Strömbergsson et al (2015) is a promising approach to identifying subtle articulatory and phonetic differences between contrasts that in transcription appear to be neutralised. However, instrumental techniques such as EPG will remain an important source of information about the articulatory features that might underlie such differences.…”