Design and Development of a Speech Intelligibility Test Based on Pseudowords in French: Why and How?

Purpose The current intelligibility tests performed on speakers with atypical speech production are limited by the ability of listeners to restore distorted sequences. This results in a measure that is overvalued when compared with the real articulatory performance. In this article, we present a new intelligibility test in order to neutralize the commonly encountered bias in traditional perception-based assessments. We present the construction of the acoustic-phonetic decoding task and its first test during a perceptual judgment test of intelligibility and during a result comparison with a global perceptual evaluation. Method We developed a very large pseudoword directory including about 90,000 forms that respect French phonotactic constraints. From this directory, we have created lists of pseudowords intended to be recorded for the constitution of the corpus. These lists are established due to an algorithm integrating predefined linguistic constraints and produced by 47 speakers (nine healthy and 38 patients). We then performed a perceptual judgment of intelligibility test with 20 listeners who transcribed these productions. Results At the end of the data processing stage, we obtained a Perceived Phonological Deviation (PPD) score for each speaker that reflects the average number of features altered per phoneme. We then compared the PPD score with a global intelligibility score derived from a global perceptual assessment of intelligibility and of the alteration severity. Conclusions The current findings confirm that a speech intelligibility test based on pseudowords in French achieves fine-grained PPD scores, which enables discrimination between patients and healthy speakers. Moreover, the PPD score is related to the global intelligibility score, especially in severity. Further studies are needed to better understand the discrimination power of this intelligibility test based on an acoustic-phonetic decoding task.