Gradient perception of children's productions of /s/ and /θ/: A comparative study of rating methods

Past studies have shown incontrovertible evidence for the existence of covert contrasts in children's speech, i.e. differences between target productions that are nonetheless transcribed with the same phonetic symbol. Moreover, there is evidence that these are relevant to forming prognoses and tracking progress in children with speech sound disorder. A challenge remains to determine the most efficient and reliable methods for assessing covert contrasts. This study investigates how readily listeners can identify covert contrasts in children's speech when using a continuous rating scale in the form of a visual analogue scale (VAS) to denote children's productions. Individual listeners' VAS responses were found to correlate statistically significantly with a variety of continuous measures of children's production accuracy, including judgements of binary accuracy pooled over a large set of listeners. These findings reinforce the growing body of evidence that VAS judgements are potentially useful clinical measures of covert contrast.