Intelligibility in Speech Disorders.

When speech produces language patterns in the mind of a perceiver that correspond with those in the mind of the speaker, it is said to be intelligible. Not all speech disorders affect intelligibility, but when they do, the need for intervention becomes acute. In spite of its importance, however, no single text has been devoted to the topic of intelligibility in speech disorders. This multi-authored volume, edited by Raymond Kent, is an attempt to remedy this omission. In the opening chapter, Nicholas Schiavetti defines intelligibility as the “match between the intention of the speaker and the response of the listener”. This match can be measured directly, for example, as the degree of correspondence between a list of words produced by a speaker and the resulting list repeated by the listener. Alternatively, it can be estimated, using scaling procedures originally developed for psychophysical research. Schiavetti reviews these scaling procedures and their applications to intelligibility assessment and concludes that the more direct measurement of word identification is preferable. At first sight, this conclusion seems at odds with the increasing use of intelligibility scaling and paired comparisons in the evaluation of hearing aids and other communication systems. As Schiavetti points out, however, intelligibility is the result of interactions among properties of the talker, the listener, and the transmission system. This text is concerned with the properties of the talker, and Schiavetti’s conclusions must be evaluated in that light. In Chapter 2, Rida Bross brings a structural linguist’s approach to the issue of intelligibility. A brief outline of the Aspectual Model of language structure is followed by an account of its application to the comparison of two alaryngeal speakers using two different prostheses. The important contribution of this chapter is that it stresses the roles of meaningful contrasts and of listener adaptation in definition and assessment. The chapter is, however, lacking in operational definitions. Moreover, the illustrative study confounds subject differences with prosthesis differences, and uses a subjective test whose advantages over more conventional articulation tests are not made clear. This chapter does not make a strong case for the special contributions of structural linguistics to the study and assessment of intelligibility in speech disorders. Gary Weismer and Ruth Martin discuss acoustic and perceptual approaches to the study of intelligibility in dysarthric subjects. They show that, in two groups with amiotropic lateral sclerosis, the incidence of two phonetic errors can account for over 90% of the variance in word identification scores. Their approach builds on similar research