Direct magnitude estimation and equal appearing interval scaling of vowel roughness

Direct magnitude estimation (DME) and equal-appearing interval (EAI) ratings of the perceived roughness of isolated sustained vowel samples (/a/ and /i/) were obtained. The linear and curvilinear relationship between the resulting EAI and DME ratings was then examined. That relationship was found to be more strongly curvilinear than linear, a characteristic of a prothetic continuum. The amount of variance accounted for by a curvilinear model of the relationship, however, was minimally more than that accounted for by a linear model. The findings thus suggest that the roughness continuum manifests no more than "a little" protheticness, if any. It does not seem clear from this initial study that there is greater validity associated with roughness ratings obtained by the DME than the EAI method. Rather, the findings suggest that a small degree of such advantage may exist, but it may be too small to be of practical consequence in many instances.