from Encyclopedia of Consciousness
Glossary
Hypnagogic state
The transitional state between wakefulness and sleep when falling asleep.Hypnopompic state
The transitional state between sleep and wakefulness when waking up from sleep.Lucid dream
A dream during which the dreamer realizes that the experience is a dream.Muscular atonia
The lack of muscle tension in voluntary muscles, causing temporary inability to move.NREM sleep
Non-REM sleep, stages of sleep without rapid eye movements and less frequent dreaming, or no dreaming at all.Psychedelic drugs
Chemical substances that affect the central nervous system and cause radical changes in overall mental function, such as hallucinations and delusions.REM sleep
Rapid eye movement sleep, a stage of sleep when the eyes move rapidly behind the closed eyelids, and when the subject is frequently dreaming.
In altered states of consciousness (ASCs), the patterns of conscious experience are different from usual, and the contents of consciousness do not reliably reflect the immediately surrounding world. Dreaming, other sleep-related hallucinations, and changes in experience caused by hypnotic suggestions are among the most typical ASCs. Exceptional states (also called higher states) of consciousness are ASCs that are emotionally positive and desirable, and some of them have spiritual meaning for the subject who experiences them. Meditation, flow, lucid dreaming, near-death experiences, and mystical states are paradigmatic exceptional states of consciousness.
Introduction
Consciousness, the stream of subjective experiences, manifests itself in many different forms, such as waking perception, dreaming, and mental imagery. Under some circumstances our subjective consciousness becomes so different from our usual experience that the state of our consciousness can be said to be qualitatively altered. The notion of altered state of consciousness (ACS) presupposes that there is some definable normal or baseline state of consciousness that is temporarily lost or somehow transformed in ACSs. What exactly is the normal state of consciousness and what counts as an altered state is difficult to define precisely and therefore continues to be a matter of debate. In the following, different definitions of altered state are first considered and then the major phenomenological features of the most significant ASCs are reviewed.
Some altered states are called exceptional or higher states of consciousness. The notion of a ‘higher’ state of consciousness suggests that different ASCs can be ordered in a hierarchical manner such that some altered states are lower or deficient in comparison with the ‘normal’ state of consciousness (say, hallucinations induced by high fever or the delirium caused by heavy drinking), whereas others, the higher states, are in some sense better, more desirable, or perhaps spiritually more advanced than the normal state. The so-called higher states are usually experienced as positive and personally significant. Many of them are closely related to religious and mystical experiences and thus are among the most intriguing ASCs. The major phenomenological features of exceptional and higher states will be reviewed and possible explanations for them explored.
In the scientific study of consciousness, ASCs may shed light on aspects of consciousness that remain otherwise hidden. Therefore, they constitute a unique source of empirical evidence for theories and models of consciousness. They may also reveal the underlying brain mechanisms of some aspects of consciousness that would be difficult or impossible to study by focusing only on the normal state of consciousness.
What Is an ASC?
All definitions of ASC take for granted that there is a normal baseline state of consciousness, and that any ASC only temporarily deviates from this normal state in some crucial manner. Hence, an ASC is a temporary, reversible state that typically lasts from a few minutes to at most a few hours. Permanent, irreversible changes in conscious experience, as in psychiatric or neurological disease, are usually not counted as ASCs.
In an ASC, what exactly is the nature of the deviation from the normal state? Can it be precisely defined so that a distinguishing feature (or a set of such features) can be pointed out that separates all the ASCs from the typical normal state of consciousness? Attempts to define the concept of ASC and the empirical criteria that separate ASCs from the normal state have been put forward, but it remains unclear if any of these definitions is successful in drawing a clear line between normal and ASCs.
Typically, the ‘normal,’ unaltered state of consciousness (henceforth NSC) is taken to be the state where we are awake, alert, perceptually aware of our own self and of the physical and the social environment, and capable of rational thought and smooth behavioral interactions with the environment. Our thought processes, sensory and perceptual representations, emotional experiences and reactions, as well as current beliefs reflect our current situation in a relatively realistic manner.
When in the NSC our thoughts and beliefs are not delusional, our sensations and perceptions are not hallucinatory, our emotional experiences and expressions are not overly exaggerated, and our voluntary mental activities and external behavior is under control and not entirely inappropriate for the physical and the social situation in question. If any of these features are however present in our experience or behavior, they may be signs of an ongoing ASC.
Still, this list of potential signs of an ASC is hardly a good definition of the concept. We should expect the definition of the concept of ASC to draw a clear line between the paradigmatic NSC and all the different ASCs. Thus, the ideal definition should focus on the common core of all the different types of ASCs, and also connect the notion of an ASC to an overall conceptual or theoretical framework in the science of consciousness. In the following sections we will consider different attempts to define the common core of all ASCs.
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