Disturbances of perception and thought process fall into a broad category of symptoms referred to as psychosis. The threshold for determining whether thought is impaired varies somewhat with the cultural context. Like anxiety, psychotic symptoms may occur in a wide variety of mental disorders. They are most characteristically associated with schizophrenia, but psychotic symptoms can also occur in severe mood disorders.
One of the most common groups of symptoms that result from disordered processing and interpretation of sensory information are hallucinations. Hallucinations are said to occur when an individual experiences a sensory impression that has no basis in reality. Hallucinations may be auditory, olfactory, gustatory, kinesthetic, tactile, or visual. For example, auditory hallucinations frequently involve the impression that one is hearing a voice. In each case, the sensory impression is falsely experienced as real.
A more complex group of symptoms resulting from disordered interpretation of information consists of delusions. A delusion is a false belief that an individual holds despite evidence to the contrary. A common example is paranoia, in which a person has delusional beliefs that others are trying to harm him or her. Attempts to convince the person that these beliefs are unfounded typically fail and may even result in the further entrenchment of the beliefs.
Hallucinations and delusions are among the most commonly observed psychotic symptoms. Symptoms of schizophrenia are divided into two broad classes: positive symptoms and negative symptoms. Positive symptoms generally involve the experience of something in consciousness that should not normally be present. For example, hallucinations and delusions represent perceptions or beliefs that should not normally be experienced. In addition to hallucinations and delusions, patients with psychotic disorders such as schizophrenia frequently have marked disturbances in the logical process of their thoughts. Specifically, psychotic thought processes are characteristically loose, disorganized, illogical, or bizarre. The severe disturbances of thought content and process that comprise the positive symptoms often are the most recognizable and striking features of psychotic disorders such as schizophrenia or manic depressive illness.
Common manifestations of schizophrenia
However, in addition to positive symptoms, patients with schizophrenia and other psychoses have been noted to exhibit major deficits in motivation and spontaneity that are referred to as negative symptoms. While positive symptoms represent the presence of something not normally experienced, negative symptoms reflect the absence of thoughts and behaviors that would otherwise be expected. Concreteness of thought represents impairment in the ability to think abstractly. Blunting of affect refers to a general reduction in the ability to express emotion. Motivational failure and inability to initiate activities represent a major source of long-term disability in schizophrenia. Anhedonia reflects a deficit in the ability to experience pleasure and to react appropriately to pleasurable situations. Positive symptoms such as hallucinations are responsible for much of the acute distress associated with schizophrenia, but negative symptoms appear to be responsible for much of the chronic and long-term disability associated with the disorder.