Professor David Lewis outlines a major cognitive symptom of schizophrenia, which is executive dysfunction - an inability to exert control over behavior.
In addition to positive symptoms and negative symptoms, one of the core features of schizophrenia are disturbances in cognitive processes. One type of cognitive process that seems to be commonly disturbed in the illness is so called executive processes, which basically represent the ability to exert control over thought and behavior. A typical example of this is the ability to inhibit what might be called a prepotent or preprogrammed response. Individuals with schizophrenia seem to be impaired in that ability. Another area of cognitive control is the ability to be given a small bit of information, transiently keep it in mind, and manipulate it in order to guide thought or behavior. So, an example of that would be being given a phone number to remember, then using that information to go and place the phone call, and to be able to keep that information in mind in order to execute the behavior. Individuals with schizophrenia tend to have disturbances in, not specifically the ability to make a phone call, but in the ability to transiently maintain and manipulate information in order to guide their thought logically, their speech logically, and to perform in a way that is appropriate for their environment.