This book is the fruit of a study group on perception and action that worked at the Center for Interdisciplinary Research (ZiP) of the University of Bielefeld, FRG in the academic year 1984-1985. We express our gratitude to the ZiF for hosting the group and for providing fmancial and organizational support for its scientific activities, including a meeting of the authors of the present volume that took place at the ZiF in July 1986. This is/ the study group's last common product, and it took considerable time to give the book its fmal shape. Most of the editing was done while one of us (0. N.) was a Fellow at the Netherlands Institute for Advanced Study in the Humanities and Social Sciences (NlAS) during the academic year 1987-1988. Thanks are due to NIAS for its generous support. We also thank all our friends and colleagues who contributed to the book.