The six years since the appearance of the first edition of this book have been exciting ones for child psychology. Systematic research has in­creased the probably validity of many statements that were largely spec­ulative only five years ago. Other statements must now be revised or deleted in the face of new evidence. Furthermore, several previously neglected problem areas in human development have been subjected to the scrutiny of more empirical research, and some important topics, which had been minimally discussed because of insufficient information, can now be elaborated. Among these topics are constitutional differences among neonates, perceptual and cognitive development, the relation be­tween personality and intellectual development, and the relation between physical changes and psychological conflicts during the adolescent period.
A major innovation in this second edition is the extensive use of longi­tudinal case material from the files of the Fels Research Institute. The development of two boys will be described in detail in order to give concrete illustrations of some of the processes emphasized in the book. It is hoped that this in vivo documentation will give the student a richer and more tangible appreciation of the complexity of human development.
The theoretical orientation remains the same. The authors still believe that contemporary learning theory offers the best method for the analysis of behavior. It will be noted, however, that the learning theory concept of reinforcement has been liberalized in order to account most parsimo­niously for certain recent research findings on direct brain stimulation and on the consequences of sensory deprivation.