Direct magnitude estimation and interval scaling of hypernasality

Hypernasality is most commonly assessed using equal-appearing interval (EAI) scaling. Recently, the validity of EAI scaling for the evaluation of hypernasality has been questioned. The issue of validity rests on the psychophysical nature of the dimension to be rated. The purpose of this study was to compare EAI scaling with direct magnitude estimation (DME), in order to determine whether EAI scaling is a valid procedure for the evaluation of hypernasality. Connected speech samples from 20 individuals with repaired cleft palate and hypernasality were used. Twenty listeners undertook the listening tasks, which included EAI scaling, DME with modulus (DME-M), and DME without modulus (DME-WM). The results showed a curvilinear relationship between EAI and DME-M and between EAI and DME-WM, suggesting that EAI may not be a valid method for the evaluation of hypernasality; DME is recommended.