Only within the past decade has the subject of consciousness been reestablished as a legitimate area of central concern in the behavioral sciences, following its virtual disappearance from the literature during the strongly behaviorist era of the 1950s and early 60s. A number of factors can be identified which helped to usher in the new Zeitgeist out of which the present volume has emerged. These include new developments in the area of species-specific learning which have called certain behavioral principles into serious question; the growth of the developmental-maturational perspective; perceptual research which substantiated constructivist concepts; and contemporary work in the general area of self-regulation which indicated that changes in certain physiological parameters can have significant behavioral consequences. A more detailed discussion of each of these factors can be found in the chapter by R. J. Davidson. However, it should be noted here that what was of major significance in all of these advances was a refocusing of scientific attention on processes within the organism which significantly modulate both its perception of and response to the environment.