Their content may include a variety of themes (e.g., persecutory, referential, somatic, reli- gious, grandiose). Persecutory delusions (i.e., belief that one is going to be harmed, harassed, and so forth by an individual, organization, or other group) are most common. Referential delusions (i.e., belief that certain gestures, comments, environmental cues, and so forth are directed at oneself) are also common. Grandiose delusions (i.e., when an individual believes that he or she has exceptional abilities, wealth, or fame) and erotomnnic delusions (i.e., when an individual believes falsely that another person is in love with him or her) are also seen.
Nihilistic delusions involve the conviction that a major catastrophe will occur, and somatic delusions focus on preoccupations regarding health and organ function.
Delusions are deemed bizarre if they are clearly implausible and not understandable to same-culture peers and do not derive from ordinary life experiences. An example of a bi- zarre delusion is the belief that an outside force has removed his or her internal organs and replaced them with someone else’s organs without leaving any wounds or scars. An ex— ample of a nonbizarre delusion is the belief that one is under surveillance by the police, de- spite a lack of convincing evidence. Delusions that express a loss of control over mind or body are generally considered to be bizarre; these include the belief that one’s thoughts have been "removed” by some outside force (thought withdrawal), that alien thoughts have been put into one’s mind (thought insertion), or that one’s body or actions are being acted on or manipulated by some outside force (delusions of control). The distinction between a de- lusion and a strongly held idea 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.
Hallucinations are perception-like experiences that occur without an external stimulus.
They are vivid and clear, with the full force and impact of normal perceptions, and not under voluntary control. They may occur in any sensory modality, but auditory halluci- nations are the most common in schizophrenia and related disorders. Auditory hallucina- tions are usually experienced as voices, whether familiar or unfamiliar, that are perceived as distinct from the individual’s own thoughts. The hallucinations must occur in the con- text of a clear sensorium; those that occur while falling asleep (hypnagogic) or waking up (hypnopompic) are considered to be within the range of normal experience. Hallucinations may be a normal part of religious experience in certain cultural contexts.
Disorganized thinking (formal thought disorder) is typically inferred from the individual’s speech. The individual may switch from one topic to another (derailment or loose associa- tions). Answers to questions may be obliquely related or completely unrelated (tangential— ity). Rarely, speech may be so severely disorganized that it is nearly incomprehensible and resembles receptive aphasia in its linguistic disorganization (incoherence or ”word salad").
Because mildly disorganized speech is common and nonspecific, the symptom must be se- vere enough to substantially impair effective communication. The severity of the impair- ment may be difficult to evaluate if the person making the diagnosis comes from a different linguistic background than that of the person being examined. Less severe dis- organized thinking or speech may occur during the prodromal and residual periods of schizophrenia.
Grossly disorganized or abnormal motor behavior may manifest itself in a variety of ways, ranging from childlike ”silliness” to unpredictable agitation. Problems may be noted in any form of goal-directed behavior, leading to difficulties in performing activities of daily living.