The term "hallucinogenic" is to be understood as referring to mental imagery of a phenomenal (i.e., experiential) type that is difficult to describe in words. Richardson suggested that Perky (1910) grasped an essential quality when she described a class of images that involve "concentrated and quasi-hypnotic attention with inhibition of associations" (Perky in Richardson, 1969, p. 94). This means that hallucinogenic imagery is only loosely controlled by conscious intentions to have imagery conform to the expectations of reality. This makes them distinct from memory or imagination images, which are generally under a greater degree of conscious control.
Hallucinations, as Richardson points out, are sometimes thought to be the most clearly delineated of all imagery types, since by definition hallucinations imply that the subject is fooled and mistakes a mental image for a percept. But Richardson also remarks that being fooled admits of degrees. An important difference between the psychotic and the normal person is that the normal person can eventually recognize that a hallucination is a mistake (see Richardson, 1969, pp. 113-118). In the less extreme forms of hallucinogenic states, the subject is completely aware that the events being experienced are not real. Often, the subject is aware that what is experienced could not happen in reality, however convincing the imagery may seem.
Typically, this class of mental images involves the objective preceding condition of a reduction of ordinary sensory input while conscious awareness continues to operate in a normal or near normal fashion (Richardson, 1969, p. 119). A physiological explanation for hallucinogenic imagery is that areas of the brain near the sensory areas are over-active in relation to initial stimulus processing centers. This causes parts of the brain to synthesize insufficient sensory data into conscious forms that would ordinarily not reach consciousness.
Examples of hallucinogenic imagery are perhaps the best indication of what is meant by the term. These include:
1. Hypnagogic imagery. Prior to sleep, in the state between wakefulness and sleep, many people (about 33%, see Richardson, 1969, p. 129) experience mental images that are vivid and autonomous, but are not yet dreams.
Hypnagogic images, according to some, are the result of the visual system "attempting to make sense" of the visual input still available to the eyes when the mind is drifting toward sleep. Even in very low ambient light levels, light penetrates the eyelids, making the patterns of blood flow through them visible. This is the basis for an "interpretation" by the visual system. The visual system may attempt to "force" the input to correspond to, say, a geometrical pattern, or the semblance of some object. Dream images or memory images may intrude into such images.
2. Hypnopompic imagery. Prior to waking up, a state similar to the hypnagogic state frequently occurs. Mental imagery in this state again exhibits autonomy.
3. Drug-induced imagery. LSD, mescaline and many other drugs produce vivid imagery.
4. Photic Stimulation imagery. If the retinae are stimulated with rhythmic low-level light emission, a hypnotic state may be induced in which geometric patterns and other recognizable images are seen.
5. Perceptual Isolation imagery. Perceptual isolation studieshave demonstrated that in the total absence of sensory input the nervous system creates mental imagery. These mental images include light patches, patterns and more elaborate dream-like events.
6. Dreams. Very few people claim not to have dreams. Of those who claim not to, it has been shown that they in fact have them and can remember them if they are awakened during a REM sleep phase (Richardson, 1969, p. 128). Dreams, of course, come in every degree of vividness and usually involve eye movements, another indication that they, like other hallucinogenic forms of imagery, involve stimulation of sensory or near-sensory areas of the brain by other brain areas. Dreams, though usually automous, sometimes seem to admint of some degree of conscious control.
Dreams and Reality.
Many aspects of hallucinogenic images remain mysterious and confounding. Dreams, for example, seem to have no evolutionary purpose. They do not give us information about our environment. Why then do they exist? Furthermore, dreams can sometimes fool us, sometimes causing us to (temporarily) mistake these images for actual percepts.
Freud, of course, and many others, have offered us explanations about the purposes of dreams. Speculation about the meaning or purpose of dreams is beyond the scope of these pages. However, we do not need to understand their purposes to make some clinical observations about
We have seen that both after-images and eidetic images cannot be consciously controlled. This suggests, at the physical level, that dream imagery involves "higher" centers of the brain; that is, those centers that are under conscious control. As we progress from the physiologically "hard-wired" forms of imagery toward those forms of imagery that can be willed (memory, imagination, and thought images), we apparently activate higher and higher levels of brain activity, more or less on a continuum.
We can see this continuum at the psychological level as well: when dreams are under some degree of conscious control, it indicates that one is aware that one's mind is involved in a creative, non-perceptual process. There appear to be modes of awareness, then, in which the conscious mind is aware that a qausi-sensory image "is not quite a percept" and may therefore be subject to conscious control. While some dreams may not fall into the category of "willed" psychic events, neither are they always entirely "automatic."
Hence, dreams appear to be a half-way point, both neurophysiologically and psychologically on the continuum from hard-wired responses to consciously-directed abstract thought.
As for the second observation above, the lack of coherence in dreams, this may be one of the clues that provides our minds use to reach the conclusion that "this is only a dream."
Although the above qualitative aspects MAY apply to dream experiences, they are by no means universal. Many people report that dreams are fully as vivid, or forceful as ordinary experience, and that what happens in them is not a matter of conscious control. In extreme cases, people confuse vivid dreams with reality and may insist that strange events, such as
*NOTE: In the chart of imagery types, a "NO" was entered under CONSCIOUS CONTROL. This is still generally true of hallucinogenic images as a class. Dream images, in any event, are probably only rarely under conscious control, and when they are, are "only loosely controlled by conscious intentions to have imagery conform to the expectations of reality" (see first paragraph of this page).
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