The Spiral After-Effect presents the visual phenomenon of the spiral after-effect in clinical investigations. This book explains how and under what conditions the illusion happens or can be modified. Organized into eight chapters, this book begins with an overview of the features of illusion that are similar to many of the characteristics of other movement perceptions, including vividness, velocity, and persistence. This text then examines the complex structure and the geometric function of the inducing stimulus. Other chapters consider the effects of drugs on the spiral illusion, which is rather strange when one considers the wide use of the phenomenon in patient groups who may be receiving substantial admixtures of compound for therapeutic purposes. This book discusses as well the relationship between intelligence and perception of the spiral after-effect. The final chapter deals with the conditioned after-effect. Clinical psychologists and readers who are interested in personality research will find this book useful.