The relationship between the Nasality Severity Index 2.0 and perceptual judgments of hypernasality

Objective. For decades, researchers have been searching for the most ideal assessment technique in order to diagnose resonance disorders and to decide on the most apposite treatment. As speech is fundamentally perceptual in nature, perceptual assessments have been traditionally applied to evaluate speech disorders. However, several variables can influence listeners’ perception of resonance which may limit the reliability and validity of perceptual judgments. Consequently, numerous indirect assessment techniques were developed to complement and objectify perceptual assessments. Nevertheless, no indirect technique can yet closely reflect the capabilities of the human ear. A possible solution to sidestep the limitations of single indirect instrumental assessment techniques is the combination of different variables into a multiparametric index. The Nasality Severity Index 2.0 (NSI 2.0) is based on this point of view and forms a new, multiparametric approach in the identification of hypernasality. The present study aimed to investigate the correlation between the NSI 2.0 scores and the perceptual assessment of hypernasality. Methods. Speech samples of 35 patients, representing a range of nasality from normal to severely hypernasal, were rated by four expert speech-language pathologists using visual analogue scaling (VAS) judging the degree of hypernasality, audible nasal airflow (ANA) and speech intelligibility. Inter- and intra-listener reliability was verified using intraclass correlation coefficients. Correlations between NSI 2.0 scores and its parameters (i.e. nasalance score of an oral text and vowel /u/, voice low tone to high tone ratio of the vowel /i/) and the degree of hypernasality were determined using Pearson correlation coefficients. Multiple linear regression analysis was used to investigate the possible influence of ANA and speech intelligibility on the NSI 2.0 scores. Results. Overall good to excellent inter- and intra-listener reliability was found for the perceptual ratings. A moderate, but significant negative correlation between NSI 2.0 scores and perceived hypernasality (r=-0.64) was found, in which a more negative NSI 2.0 score indicates the presence of more severe hypernasality. No significant influence of ANA or intelligibility on the NSI 2.0 was withheld. Conclusion. As the NSI 2.0 correlates well with perceived hypernasality, it provides an easy-to-interpret severity score of hypernasality which will facilitate the evaluation of therapy outcomes, communication to the patient and other clinicians, and decisions for treatment planning, based on a multiparametric approach. However, research is still necessary to further explore the instrumental correlates of perceived hypernasality. Learning outcomes: The participant will be able to describe and discuss (1) the relationship between the Nasality Severity Index 2.0 and perceptual judgments of hypernasality based on visual analogue scale ratings, (2) the possible influence of audible nasal airflow and speech intelligibility on the NSI 2.0 scores