This volume was designed to focus on the problems of perception and originally was to have been solely edited by Professor Hans-Lukas Teuber who was a member of the editorial board which initiated production of the Handbook. Accordingly, he issued invitations to a number of researchers III perception asking them to contribute chapters written in a style described III his words: " . . . Ire hope that no author lIill feel COl/strained to undertake a major search of the literature: he could Inite, instead. on an area in which he has been quite actire himset and IIhere most of the issues are immediately obt"ious to him. In this Iray, the IITiting of the chapter should be cnjoyable rather than a chore . . it should result in a personal account of the state of a given area rather than in an encyclopedic treatise . . . the field deserves this sort of summary retiell", particularly (f it is pointed toward the future and speeds the convergence of detelopments in sensory physiology and psychological studies of perception, " With the growing burden of national and international commitments includ- ing departmental headship, Professor Teuber felt that it would be wise to share the editorial responsibilities for this volume and accordingly, asked Professors Richard Held and Herschel Leibowitz to co-edit the volume with him in the same spirit as outlined in his invitation to authors. They agreed to help in this task.