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 lI'ill feel COl/strained to undertake a major search of the literature: he could In'ite, instead. on an area in which he has been quite actire himse?t~ and II'here 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