First appearing in the historical records of the ancient Mayan and Incan civilizations, various theories of multiple levels of consciousness have pervaded spiritual, psychological, medical, and moral speculations in both Eastern and Western cultures. Consciousness can be defined as human awareness to both internal and external stimuli. Because of occasional and sometimes substantial overlap between hypotheses, there have recently been attempts to combine perspectives to form new models that integrate components of separate viewpoints.
The Ancient Mayans were among the first to propose an organized sense of each level of consciousness, its purpose, and its temporal connection to humankind. Because consciousness incorporates stimuli from the environment as well as internal stimuli, the Mayans believed it to be the most basic form of existence, capable of evolution. The Incas, however, considered consciousness a progression not only of awareness but of concern for others as well.
One of the most popular Western theories is that of Sigmund Freud, medical doctor and father of psychoanalytic theory. Freud divided human consciousness into three levels of awareness: the conscious, preconscious, and unconscious. Each of these levels corresponds and overlaps with Freud's ideas of the id, ego and superego (Figure 1). The conscious level consists of all those things we are aware of, including things which we know about ourselves and our surroundings. The preconscious consists of those things which we could pay conscious attention to if we so desired, and where many memories are stored for easy retrieval. Freud saw the preconscious as those thoughts which are unconscious at the particular moment in question, but which are not repressed and are therefore available for recall and easily 'capable of becoming conscious" (for example, the "tip of the tongue" effect). The unconscious consists of those things which are outside of conscious awareness, including many memories, thoughts, and urges of which we are not aware. Much of what is stored in the unconscious is thought to be unpleasant or conflicting; for example sexual impulses which are deemed "unacceptable." While these elements are stored out of our awareness, they are nevertheless thought to influence our behavior.
While Freud's theory remains one of the best known, various schools within the field of psychology have developed their own perspectives. For example, developmental psychologists view consciousness not as a single entity, but as a developmental process with potential higher stages of cognitive, moral, and spiritual quality. Social psychologists view consciousness as a product of cultural influence having little to do with the individual. Neuropsychologists view consciousness as ingrained in neural systems and organic brain structures, and cognitive psychologists base their understanding of consciousness on computer science.