Psychosis: Delusions and Hallucinations (according to DSM-5)
In DSM-5 (2013; p. 87), the American Psychiatric Association characterises delusions and hallucinations as follows.
‘Delusions are [tenacious] beliefs that are not amenable to change in light of conflicting evidence.’ ‘The distinction between a delusion and a strongly held [belief] is sometimes difficult to make and depends in part on the degree of conviction with which the belief is held despite clear or reasonable contradictory evidence regarding its veracity.’ When it happens that clear or reasonable contradictory evidence is not readily available, a delusional belief is often held, nevertheless, with a degree of conviction that is excessive given the individual’s lack of access to supporting evidence.
A delusion (or, more generally, a belief) is labelled ‘bizarre’ if, in virtue of its content, ‘it is clearly implausible’, ‘not understandable to same-culture peers’, and cannot be explained in a normal manner on the basis of ‘ordinary life experiences’. ‘An example of a bizarre delusion is the [delusional belief] that an outside force has removed [one’s] internal organs and replaced them with someone else’s organs without leaving any wounds or scars.’ ‘An example of a nonbizarre delusion is the [delusional belief] that one is under surveillance by the police, despite a lack of convincing evidence’.
In relation to determining whether a given belief qualifies as a delusion, it is the degree-of-conviction-despite-evidence that is directly relevant, rather than the extent to which the content is bizarre. In this connection, the content of a belief is only relevant insofar as it bears on the normal demand for supporting evidence, or on one’s exposure to ‘clear or reasonably contradictory evidence’. To say that a belief is bizarre is, in effect, merely to say that it is clearly or reasonably contradicted by abundantly available evidence. Therefore, if a belief is held for any notable length of time, then it is more likely to qualify as a delusion if it is bizarre, but only because, in virtue of its bizarre content, it is more likely to be held despite clear or reasonable contradiction by evidence.
Certain themes are recognised in relation to the contents of delusions. On this basis, a delusion might be categorised, e.g., as persecutory, referential, grandiose, erotomanic, nihilistic, or somatic (among others).
Persecutory delusions are the most common among delusions. A persecutory delusion is a delusional belief that one is currently being, or is going to be, ‘harmed, harassed’, or otherwise thwarted or undermined ‘by an individual, organization, or other group.’ Some persecutory delusions are more specifically described as paranoid.
Referential delusions are also common among delusions. A referential delusion is a delusional belief that ‘certain gestures, comments, environmental cues’, or other potentially meaningful stimuli are somehow directed at or about one’s self.
Grandiose delusions are delusional beliefs that one is special or exceptional in some regard, such as in terms of one’s abilities, wealth, or fame.
Erotomanic delusions are delusional beliefs that another person is in love with one’s self.
Nihilistic delusions are delusional beliefs that some major catastrophe will occur.
Somatic delusions are delusional preoccupations regarding one’s health or organ function.
A delusion is generally considered bizarre if its content involves ‘a loss of control over one’s mind or body’. Among such delusions:
Thought withdrawal delusions are delusional beliefs that one’s thoughts have been “removed” by some outside force.
Thought insertion delusions are delusional beliefs that alien thoughts (i.e. thoughts that are not one’s own) have somehow been put into one’s mind.
Delusions of control are delusional beliefs that one’s body or actions are being influenced or manipulated by some outside force.
‘Hallucinations are perception-like experiences that’:
‘occur without’ the normal correspondence of ‘an external stimulus’.
‘are vivid and clear, with the full force and impact of normal perceptions’ (though typically without the multi-modal complexity of normal perceptual experiences).
‘are not under voluntary control’ (as distinct from broadly perceptual states of imagination).
Hallucinations ‘may occur in any sensory modality, but auditory hallucinations are most common’ (at least among the hallucinatory symptoms of ‘schizophrenia and related disorders’). ‘Auditory hallucinations are usually experienced as voices, whether familiar or unfamiliar, that are perceived as distinct from’ one’s own thoughts.
Hallucinations are only considered to be of diagnostic significance if they ‘occur in the context of a clear sensorium;’ in particular, ‘those that occur while falling asleep’ (hypnagogic hallucinations) ‘or waking up’ (hypnopompic hallucinations) are considered to be within the range of normal experience.’ It is also possible that hallucinations are ‘a normal part of religious experience in certain cultural contexts.’
