Chapter
Fourteen
Reality and imagination
associated with pathology, such as hearing a voice speaking one’s thoughts
aloud. Scores on the scale were approximately normally distributed (Slade
and Bentall, 1988). Later studies revealed three factors: 1) vivid or intrusive
mental events, 2) hallucinations with a religious theme, and 3) auditory and
visual hallucinations. In the first case, agency is attributed to oneself and the
experience recognised as one’s own (my daydreams), whereas in 2) and 3), the
experience is attributed to a source other than oneself, with salient social and
agent-like properties (see also Alderson-Day and Fernyhough, 2016) some-
times extending to supernatural forces (‘a voice’, ‘voice of God’) (Waters et al.,
2003). This scale has also been used to explore the rather complex relation-
ships between the tendency to hallucinate and other variables such as reality
monitoring, vividness of imagery, schizotypal personality, and susceptibility
to hypnosis.
A more recent cross-cultural estimate of hallucination based on surveys from
eighteen countries found that 5.2% of respondents had experienced a halluci-
nation in their lifetime (compared to only 1.3% reporting delusional experiences
involving paranoid beliefs about mind control, being followed, etc.), with lower
instances in low-income countries and amongst men (McGrath et al., 2015). All
this suggests that the tendency to hallucinate varies along a continuum, with
pathological cases at one end, people who never hallucinate at the other, and
most of us in between.
CONTEXTS AND CONTENTS OF HALLUCINATIONS
Hallucinations which fit Slade and Bentall’s criteria are frequently associated
with mental illness. In psychiatric conditions, including schizophrenia, bipolar
disorder, and depression, around 15% report visual hallucinations and 28%
auditory hallucinations. Rates are highest in schizophrenia, averaging around
27% and 59% respectively (Waters et al., 2014). Schizophrenia affects something
like 0.3% of the world’s population, and is difficult to define and understand; it
tends to be diagnosed differently at different times and in different countries.
Although the symptoms are highly variable, the core is a loss of the sense of
personal control. People with schizophrenia may be convinced that other peo-
ple with psychic powers are forcing their actions, or that an evil entity is con-
trolling them. The most common kind of hallucination (reported on average by
around 60% of sufferers) is hearing voices, such as aliens plotting evil deeds, or
fairies chattering in the walls. Some people with schizophrenia feel that other
people are inserting thoughts into their mind; some hear their own thoughts
being spoken out loud as though by someone else. At their strongest, these
hallucinations are detailed and compelling, uncontrollable, and experienced as
completely real (Frith, 2015).
Hallucinations are also sometimes experienced as part of the ‘aura’ which pre-
cedes a full-blown epileptic seizure. These may be visions, disturbing smells or
sounds, an intense feeling of déjà-vu, or even repeated scenes from memory or
imagination. Patterns often develop in these experiences, which may be useful
as a warning of an impending seizure and as a clue to what its triggers are or
where in the brain it begins. People with dementia may also have hallucinations,
with the type of hallucination depending on whether auditory or visual cortex, for
example, is less affected as their condition deteriorates.