This book is one of a series whose primary aim is to inform the professional speech and language clinicians and their colleagues in the caring professions. The starting point for this series was a systematic review of those topics in human communication which are essential to the development of effective treatment programmes and effective clinicians. This collection of essays is designed to present the speech student and language clinician with an integrated introduction to contemporary thought and practice in the science of speech and language pathology and intervention. It aims to provide a broad coverage of the basic issues in the field written by specialized authors from both sides of the Atlantic.