Chapter
Fourteen
Reality and imagination
and when a uniformed naval officer appears at the wheel in the
midst of a storm hundreds of miles from shore, the exhausted
lone sailor knows that no one else can really be aboard the ship.
A final distinction is between hallucinations and mental imag-
ery. Hallucinations are sometimes distinguished from imagery
by their resemblance to publicly shared perceptions rather than
private thoughts, or by their uncontrollability. If we voluntarily
imagine a tropical beach with the sound of waves lapping on
the sand, this is usually called imagery, but if the vision forces
itself on our mind and won’t go away it would be called a hal-
lucination. But even this distinction is unclear. For example, the
images that come on the borders of sleep (Chapter 15) are usu-
ally called ‘hypnagogic imagery’ rather than ‘hypnagogic hallu-
cinations’, although they are not voluntary or easily controllable.
Imaginative sensory-like experiences that occur while we read
fiction are normally called imagery too, even though they are
guided by the text and your imaginings may be intrusive and
hard to set aside, even after you put the book down. So, rather
than try too hard to delimit these categories, some prefer to
think of a continuum with true hallucinations at one end and
imagery at the other. But even this may not help if there are mul-
tiple dimensions involved.
These distinctions are discussed by British psychologists Peter Slade and Richard
Bentall (1988), who propose this working definition of a hallucination:
Any percept-like experience which (a) occurs in the absence of an
appropriate stimulus, (b) has the full force or impact of the corresponding
actual (real) perception, and (c) is not amenable to direct and voluntary
control by the experiencer.
(p. 23)This too has its problems, especially with point (b). What does the ‘full force or
impact’ mean when applied, for example, to a ghostly human figure seen climb-
ing dimly lit stairs? Many such hallucinations are described as fleeting and the
figures as transparent, but transparent people do not exist, so there is no obvious
‘actual (real) perception’ to compare this experience with.
PREVALENCE OF HALLUCINATIONS
One of the first attempts to study hallucinations in the general population was
the Society for Psychical Research’s ‘Census of hallucinations’ in the late 1800s
(Gurney, Myers, and Podmore, 1886; Sidgwick et al., 1894). This was a time when
‘spirit mediums’ were holding séances right across Europe and the USA, some
in complete darkness, with spirit voices emanating from luminous floating
trumpets, music mysteriously playing, and touches and cold breezes being felt.
Sometimes a translucent, greyish substance called ectoplasm was exuded from
the bodies of certain mediums, and even ‘materialised’ into the bodily form of
spirits (Gauld, 1968). Many were caught cheating, and mediums who wanted to
enhance their act could easily purchase muslin drapes, trumpets, luminous paint,
FIGURE 14.1 • On LSD trips the floor can turn
into a carpet of snakes, cars
into space ships, and trees
into monsters. But typically
the tripper still knows that the
monster is really a tree, and is
therefore technically having a
pseudo-hallucination, not a true
hallucination.