The advantages of studying psychological phenomena rather than psychiatric diagnoses.

This article argues that research efforts to understand the nature of the psychological processes un-derlying such psychological phenomena as formal thought disorder delusions, and hallucinations will be more suc-cessful if the phenomena themselves are studied directly than if diagnostic categories ( e.g., schizophrenia) are studied.This point is illustrated through references to the study of cognitive mechanisms underlying symptoms of schizophrenia.However. the advantages of the symptom approach are also applicable to the study of other types of psychopathology and other types of underlying mechanisms (e.g., physiological or biochemical mechanisms).In this article I argue that research efforts to understand the nature of the psychological processes underlying such psychological phenomena as formal thought disorder, de-lusions, and hallucinations will be more successful if the phenomena themselves are studied directly than if di-agnostic categories (e.g., schizophrenia) are studied.The article describes six advantages of studying psychological phenomena rather than psychiatric diagnoses.This issue is discussed mostly within the framework of the search for cognitive mechanisms underlying symptoms of schizophrenia, particularly symptoms of thought disorder.However, the advantages of the symptom approach are also applicable to the study of other types of psychopa-thology and other types of underlying mechanisms.Before the main arguments are presented, a brief discussion of thought disorder is required.Because of its centrality to schizophrenia and the number of studies de-voted to it, thought disorder is treated in detail.The discussion of thought disorder presented here depends on a clear distinction between two concepts of thought disorder: The overt phenomena, or symptoms of thought disorder, and the underlying processes (Rochester & Martin, 1979).The overt phenomena of thought disorder are the overt manifestations of disordered verbal behavior (e.g., loose associations, tangentiality, neologisms, blocking).They usually fall into one of two classes: a complaint by the listener that he or she has difficulty understanding the speaker or the presence of certain items (e.g., neologisms or associative responses) in the speaker's verbal produc-tions.The term underlying process of thought disorder refers to underlying psychological mechanisms, for ex-ample, yielding to normal biases (Chapman & Chapman, 1973) or excessive vulnerability to distraction (Oltmanns, 1978).It is important to recognize that hypotheses about underlying psychological processes of thought disorder arose from observations of the overt symptoms of thought disorder.For example, Bleuler (1911Bleuler ( /1950) ) noticed that some patients exhibited illogical and bizarre connections between ideas, clang associations, blocking, and other types of verbal anomalies, and he hypothesized that an underlying deficit in association processes was the psychological mechanism responsible for these phenomena.Similarly, Chapman noticed that some patients com-plained of difficulty concentrating, and he hypothesized an underlying attentional deficit (McGhie & Chapman, 1961).Chapman and Chapman (1973) proposed that the unusual use of words and the tendency to give associative responses observed in some patients was due to what they called an excessive yielding to normal biases.Notice that the preceding discussion of the relationship between the phenomena and processes of thought disorder made no reference to the disease of schizophrenia.It was not necessary to introduce it.However, an examination of the research literature shows that the most common experimental design adopted by investigators of thought disorder is the comparison of schizophrenic and nonschizophrenic individuals on measures of the hypothesized underlying psychological process.This approach might be called the "diagnostic category" research design.Virtually all the studies reviewed in Chapman and Chapman's ( 1973) classic review of the literature on cognitive processes in schizophrenia used this design, and it continues to be widely used.As a result, the study of the overt manifestations of thought disorder has been largely replaced by the study of the diagnostic category of schizophrenia.A few investigators have recently begun to study symptoms of thought disorder directly (e.g.,