Building a clinically relevant cognitive task: case study of the AX paradigm

Abstract

Tasks developed for basic cognitive neuroscience are often ill suited for experimental psychopathology. The development of the expectancy variant of AX continuous performance task to test theories about context processing in schizophrenia is used as an illustration of how this has been done in one research program. Four design principles are recommended: tasks should (1) have a foundation in existing literature and therefore stay as close as possible to an existing task; (2) be simple, which is frequently accomplished by paring down a task to evaluate the function of interest; (3) probe a mechanism of interest, with conditions that selectively manipulate this mechanism; and (4) have the potential to distinguish a specific deficit on the mechanism of interest from a generalized impairment. Data from a number of studies support several aspects of context-processing theory; however unpredicted results have also been reported. The development of the expectancy AX paradigm continues, and future developments that may enhance its usefulness are also described.

Fig. 1.

Context-Processing Theory Implemented With a Connectionist Model. In this model, context information is stored in the prefrontal cortex (PFC), which provides top-down support for secondary or underlearned input-output mappings as indicated by current goal states (after Servan-Schreiber et al43).

Fig. 2.

Illustrative Results From 6 Studies Using the Expectancy AX Task. Y-axis shows proportion of errors. (A) Original study. Eighteen unmedicated schizophrenia patients, 21 medicated schizophrenia patients, and 11 psychiatric controls with major depression. Long-delay performance illustrated. (B) Independent replication. Fifteen schizophrenia patients and 15 healthy controls. Combined (short- and long-delay) performance illustrated. (C) Fifty-three schizophrenia patients, 25 psychiatric controls with major depression, and 31 healthy controls. Combined performance illustrated. (D) Forty-nine schizophrenia patients, 30 patients with nonschizophrenia psychosis, and 72 healthy controls. Combined performance at index hospitalization illustrated. (E) Twenty-four schizophrenia patients, 24 healthy siblings or patients, and 36 healthy controls. Combined performance illustrated. (F) Twenty healthy volunteers undergoing pharmacological challenge. Combined performance in 3 manipulations illustrated. Pts., patients; med., medicated; unmed., unmedicated; Non-Sz, nonschizophrenia diagnoses; Rels., relatives.