It remains to be determined whether the cognitive biases associated with persecutory delusions are state or trait variables or whether a differential activation relationship exists such as in depression (Teasdale, 1988). Manipulation of the key
variables in individuals with persecutory delusions will be an important step in determining causal roles. Study of cognitive processes associated with delusions across disorders is also likely to be a valuable strategy. Delusions have been studied from a cognitive perspective in non-affective functional psychosis but they occur in many other disorders (Manschreck & Petri, 1978; Coryell & Tsuang, 1982; Cummings, 1992; Cutting, 1987; Trimble, 1992). Astrength of such a research strategy is that it facilitates investigation as to whether there are psychological processes that are specific to the occurrence of delusions in each disorder. In order to study delusion-specific factors a closely matched control group of individuals without delusions is needed; it is difficult to recruit a control group of individuals with schizophrenia who have never had delusions but the task is simpler for individuals with depression and individuals with neurological disorder. Furthermore, it is significant for the new model of persecutory delusions that delusions in mood disorders such as bipolar disorder and depression are associated with emotion (by diagnostic definition). This is a clear indication of direct
roles for emotion in delusion formation and maintenance.Finally, the model highlights the interaction between psychotic processes, nonpsychotic processes, and the environment; cognitive investigation into how each affects the other will be of great interest.