ABSTRACT
As discussed in Chapter 1, the heterogeneity of symptoms associated with the diagnosis of schizophrenia, and the difficulties concerning the reliability and validity of the diagnosis, have led a number of authors to suggest that research examining the aetiology and treatment of psychosis should focus on the individual symptoms rather than broadly defined clinical syndromes. Positive symptoms are often viewed as the defining symptoms of the syndrome of schizophrenia, particularly within diagnostic schemes that emphasise the Schneiderian concept of first rank symptoms (Schneider, 1959). These symptoms include auditory hallucinations (audible thoughts, a discussion or argument about the patient or voices describing the patient’s ongoing activity), somatic passivity experiences (the patient experiences bodily sensations as being caused by an external agent), thought insertion (the patient experiences thoughts as being put in his or her mind by an external agent), thought withdrawal (the patient experiences thoughts being removed by an external agent) and thought broadcast (the patient experiences thoughts as being transmitted to other people). Delusional perception (a normal perception is interpreted as having special, highly personal significance) was also considered a first rank symptom by Schneider, along with delusions that the patient’s actions, impulses or feelings are being imposed or controlled by an external agent. However, other types of delusions, for example delusions of persecution, are considered to be positive symptoms within most modern diagnostic schemes. The status of thought disorder (or speech/language disorder, including tangential thinking and word salad) is more ambiguous. Most factor analytic studies have shown that this type of symptom belongs to a disorganisation factor that also includes subjective cognitive impairment, and which is quite independent of the positive symptoms (Liddle, 1987). However, some researchers have argued that psychotic speech and language disorders can be divided into two types-positive thought, language and communication disorder (mainly evidenced by incoherence) and negative thought, language and communication disorder (mainly evidenced by poverty of speech and poverty of content of speech) which belongs to the negative symptoms (Andreasen, 1979b).
