Measuring differential deficits in auditory selective attention in schizophrenia

Using information processing models, with the computer as an analog, researchers have attempted to understand apparent attention deficits associated with schizophrenia. Opposing theories have developed that assume that attention dysfunction either begins early in the information processing sequence (early filtering) when simple perceptual characteristics are used to select information, or later in the sequence, when more complex combinations of perceptual characteristics are used (late filtering). Experimental findings from studies which have examined deficits occurring early in the sequence have a mixed pattern of results, but generally support early filter dysfunction models. There is a paucity of research findings focusing on later filter operations, and the results are not interpretable due to methodologic flaws.

The present study used experimental tasks designed to assess both early and later filter operations. These tasks were equated for difficulty level, to determine the relative degree of dysfunction in either of the filtering mechanisms. Early filter dysfunction was assessed by using a female voice as the relevant perceptual characteristic for selecting input, while distracting stimuli was presented by a male voice. The later filter operation was assessed by having subjects select odd digits which were recorded along with an ongoing presentation of distracting even digits. Performances were compared to a baseline, non-distraction condition for three groups: schizophrenia patients, psychotically depressed patients, and normal controls.

Neither the normal nor the psychotically depressed subjects were significantly impaired by distraction in either of the experimental conditions, relative to base line, although the depressed group generally performed significantly less well than normal. The schizophrenic group performed significantly less well than either of the other groups, and this impairment became more pronounced on the two tasks in which filtering was required. The schizophrenia group performed less well on the early filter task than was seen on the late filter task. These results lend support to the early filter deficit theory, and suggest that schizophrenia is also associated with conceptually oriented, late filtering operation deficits.