The concept of consciousness played a central role in Vygotsky's research and theory. Unfortunately, with the advent of behaviorism, consciousness fell into disfavor. One of the major obstacles in studying consciousness is that there is no single acceptable definition of the term. Various researchers have dealt with five different aspects of consciousness that are relevant to the study of cognitive functioning: awareness, automaticity, volition, primacy and verbalizability. Vygotsky's theory offers three important insights which can make the study of consciousness viable. He suggests (1) that the problem of consciousness should be examined from a functional perspective, (2) that such study use the generic method, and (3) that consciousness should be unified as a whole. The five dimensions of consciousness that have been studied separately can be integrated into a single unified hierarchical model of consciousness. This model places consciousness at the highest level; at the next level are two cognitive components whose interrelationship changes with development; and at the level below this are the various cognitive functions such as memory, attention, perception, and imagery or thinking. (HOD)