A false perception of sensory vividness arising without the
stimulus of a corresponding sense impression. In this it differs
from illusion, which is merely the misinterpretation of an actual
sense perception. Visual and auditory hallucinations are the
most common, but hallucinations of the other senses may also
be experienced. Human figures and voices most frequently
form the subject of a hallucination, but in certain types other
classes of objects may be seen, as, for instance, the rats and insects
of delirium tremens.
Although hallucination is often associated with various mental
and physical diseases, it may nevertheless occur spontaneously
while the agent shows no departure from full vigor of
body and mind. It may also be induced (i.e., in hypnotism) in
a high percentage of subjects. The essential difference between
sane and insane hallucinations is that in the former case the
agent can, by reflection, recognize the subjective nature of the
impression, even when it has every appearance of objectivity,
whereas in the latter case the patient cannot be made to understand
that the vision is not real.
Until the early twentieth century, hallucinatory percepts
were regarded merely as intensified memory images; however,
the most intense of ordinary representations do not possess the
sensory vividness of the smallest sensation received from the
external world. It follows that other conditions must be present
besides the excitement of the brain, which is the correlate of
representation. The seat of excitement is the same in actual
sense perceptions and in memory images, but in the former the
stimulus is peripherally originated in the sensory nerve, whereas
in the latter it originates in the brain itself.
When a neural system becomes highly exciteda state
which may be brought about by emotion, ill health, drugs, or
a number of other causesit may serve to divert from their
proper paths any set of impulses arising from the sense organs.
Because any impulse ascending through the sensory nerves
produces an effect of sensory vividnessnormally, a true perceptionthe
impulses thus diverted gives to the memory
image an appearance of actuality not distinguishable from that
produced by a corresponding sense impressiona hallucination.
In hypnosis a state of cerebral dissociation is induced,
whereby a neural system may be abnormally excited and hallucination
thus readily engendered. Drugs, especially hallucinogens,
which excite the brain, also induce hallucinations.
In 1901 the British physician Sir Henry Head demonstrated
that certain visceral disorders produce hallucinations, such as
the appearance of a shrouded human figure. The question of
whether there is any relationship between the hallucination
and the person it represents is, and has long been, a vexing
one. Countless well-authenticated stories of apparitions coinciding
with a death or some other crisis are on record and
would seem to establish some causal connection between them.
In former times apparitions were considered to be the doubles
or ethereal bodies of real persons, and Spiritualists believe
that they are the spirits of the dead (or, in some instances, of
the living) temporarily forsaking the physical body.
The dress and appearance of the apparition does not necessarily
correspond with the actual dress and appearance of the
person it represents. Thus a man at the point of death, in bed
and wasted by disease, may appear to a friend miles away as if
in ordinary health and wearing familiar clothing. Nevertheless,
there are notable instances where some remarkable detail of
dress is reproduced in the apparition. It seems clear, however,
that it is the agents general personality that is, as a rule, conveyed
to the percipient, and not, except in special cases, his or
her actual appearance.
It has been suggested that those images that do not arise in
the subliminal consciousness of the agent may be telepathically
received by him or her from other minds. A similar explanation
has been offered for the hallucinatory images that many people
can induce by crystal gazing or staring into a pool of water, a
drop of ink, or a magic mirror in search of information about
scenes or people they know nothing about.
Collective hallucination is a term applied to hallucinations
shared by a number of people. There is no firm evidence, however,
of the operation of any agency other than suggestion or
Hallucination and Psychical Research
One of the most succinct definitions of hallucination occurs
in Phantasms of the Living (2 vols., 1886), by Edmund Gurney,
F. W. H. Myers, and Frank Podmore percepts which lack,
but which can only by a distinct reflection be recognised as lacking,
the objective basis which they suggest. If the sensory perception
coincides with an objective occurrence or counterpart,
the hallucination is called veridical, (truth-telling), as in the
phantasm of the dying. If the apparition is seen by several people
at the same time, the case is called collective veridical hallucination.
In the years following the foundation of the Society for Psychical
Research (SPR), London, the hallucination theory of
psychic phenomena was in great vogue. If no other explanation
was available the person who had had a supernormal experiHallowed
Grounds Fellowship of Spiritual . . . Encyclopedia of Occultism & Parapsychology 5th Ed.
ence was told it was a hallucination, and if several people testified
to the same occurrence it was said that the hallucination
of one was communicated to the others. Sir William Crookes
counters that idea in his Researches in the Phenomena of Spiritualism
(1870) The supposition that there is a sort of mania or delusion
which suddenly attacks a whole roomful of intelligent
persons who are quite sane elsewhere, and that they all concur,
to the minutest particulars, in the details of the occurrences of
which they suppose themselves to be witnesses, seems to my
mind more incredible than even the facts which they attest.
Charles Richet, in Thirty Years of Psychical Research (1923),
omits hallucination completely in his discussion of metapsychical
phenomena (a term for paranormal). He believed that hallucination
should be reserved to describe a morbid state when
a mental image is exteriorized without any exterior reality. According
It is extremely rare that a person who is neither ill, nor
drunk, nor hypnotised should, in the walking state, have an auditory,
visual, or tactile illusion of things that in no way exist.
The opinion of alienists that hallucination is the chief sign of
mental derangement, and the infallible characteristic of insanity
seems to me well grounded. With certain exceptions (for
every rule there are exceptions) a normal healthy individual
when fully awake does not have hallucinations. If he see[s] apparitions
these correspond to some external reality or other. In
the absence of any external reality there are no hallucinations
but those of the insane and of alcoholics.
An instance recounted by Sir John Herschel did not conform
to Richets idea. He had been watching with some anxiety
the demolition of a familiar building. On the following evening,
in good light, he passed the spot where the building had
stood. Great was my amazement to see it, he wrote, as if still
standing, projected against the dull sky. I walked on, and the
perspective of the form and disposition of the parts appeared
to change as they would have done if real.
In the case of hauntings where a ghost is seen, Gurney suggests
that a person thinking of a given place that is at the time
actually experienced in sense perception by others may be imparting
into the consciousness of the others a thought existing
in his own.
Of course, data provided by a registering apparatus or photography
may rule out the hallucination theory as applied to
hauntings, provided that there is some proper scientific control.
Similarly, if objects are displaced, as in poltergeist cases,
the theory of hallucination is no longer tenable. As Andrew
Lang writes in Cock Lane and Common Sense (1896), Hallucinations
cannot draw curtains, or open doors, or pick up books, or
tuck in bedclothes or cause thumps.
The things seen during a psychic experience of an otherwise
normal person should also be distinguished from the hallucinations
of the mentally deranged, of the sick, drunk, or drugged.
The latter are not veridical, nor telepathic, nor collective. In
the Census of Hallucinations, published in the Proceedings of
the SPR (1894), the committee excluded, as far as possible, all
pathological subjects. J. G. Piddington (see Proceedings, vol. 19),
in testing this census for cases that would show the same nature
as hallucinations arising from visceral diseases, concluded that
there was not a single case in the census report that fell into line
with the visceral type.
In hypnotic hallucinations the hypnotized subject may see
apparitions if so suggested and may not see ordinary people
who are in the same room. But the subject may hear the noises
they make, see the movement of objects they touch, and be
frightened by what appears to be poltergeist phenomena. If the
suggestion is posthypnotic the subject may also see a phantom
shape when given a signal or at a prescribed time.
The visions seen by some people on the verge of sleep were
called hypnagogic hallucinations by F. W. H. Myers. The afterimages
on waking from sleep he named hypnopompic hallucinations.
A comprehensive study of both classes of phenomena
was published by G. E. Leaning in the Proceedings of
the SPR, (vol. 35, 1926).
The difference between hallucination and illusion is that
there is an objective basis for the illusion, which is falsely interpreted.
In hallucination, although more than one sense may be
affected, there is no external basis for the perception.
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