First published in 1979. The aim of this series of Tutorial Essays, of which the present book is the second volume, is to enable the specialist in one area to discover in as painless a way as possible what his colleagues in other parts of the field are up to: New discoveries, methods and theories in one speciality often have important implications for work in others. The essays are also intended to be intelligible and useful to graduate students and advanced undergraduates seeking an introduction to a topic. In this volume Bow Lett describes modern work on an old topic, delay learning in animals, and discusses its implications for theories of learning. Mark Georgeson expounds an important new approach to vision, the application of Fourier analysis: His chapter contains an exceptionally clear exposition of the ideas underlying this technique written for the reader with little mathematical knowledge. Dennis Holding provides a synthesis of the many different approaches to the problem of echoic memory, and Gregory Jones presents some new ideas on associative memory which make many previously puzzling results fall into place.