Organic variation and voice quality

Abstract

This thesis examines the contribution of organic factors to voice quality. As background, the first part of the thesis examines the structure and properties of the tissues which make up the vocal apparatus, and discusses the growth patterns of these tissues in normal development, and in response to trauma and disease. The normal changes in the vocal apparatus which occur during the human life cycle are summarised.

The second part of the - thesis focusses on some experimental investigations into the relationship between specific types of organic variation and voice quality. One problem in this field has been the lack of objective means of voice quality analysis, so that a subsidiary aim of the thesis has been the development and testing of appropriate voice assessment procedures. Two techniques for voice quality evaluation were used in this study; a perceptually based scheme and one using acoustic measurements. The development and use of these procedures are discussed, and examples of their application are discussed. Two main types of organic disorder are used to illustrate the links between measurable voice quality features and organic factors. The first of these, Down's Syndrome, involves a global disruption of growth and development, which results in a well documented set of physical anomalies. Voice quality findings for Down's Syndrome speakers seem to be clearly related to their organic features. The second class of disorder involves structural changes in the vocal folds, such as laryngeal cancer. Acoustic analysis of phonation in the presence of these disorders is discussed, with a view to the future development of acoustic voice analysis as a means of detecting vocal fold pathology.