Word intelligibility testing using phonetic contrasts for Japanese speakers with articulation disorders

Abstract

We developed a single-word intelligibility test capable of estimating the intelligibility level and assessing types of articulatory errors underlying the reduced intelligibility of a speaker. The test was designed for Japanese speakers with articulation disorders based on the idea of Phonetic Intelligibility Testing proposed by Kent et al. (1989). The present study investigated the clinical usefulness of our test based on its administration to 10 speakers with dysarthria. Fifty college students participated in the experiment as judges (five for each speaker). They listened to 10 dysarthric speech samples of 80 words, and were instructed to guess which of five presented words was uttered by the speakers. The five words consisted of one word read by the speakers and four words which contained a phoneme different from the word read by the speakers. The results indicated high intrajudge and interjudge reliability using the test, while significant relativity with other word-level intelligibility test suggested that our test is valid for quantifying the intelligibility of dysarthric speech. Articulatory error analysis using the 24 phonetic contrasts was shown to offer useful information when clinicians plan a rehabilitation approach. For example, our test demonstrated that two speakers who showed the same intelligibility level exhibited different patterns of articulatory errors. We concluded that our test is a useful measure for clinical assessment of articulatory disorders.