Neuropsychological concomitants of major depression
The limits of the cognitive deficits associated with depression were investigated with a battery of standardized neuropsychological tests. In addition, the various perspectives regarding the mechanism responsible for the cognitive changes were investigated using a dual-task paradigm. By comparing a clinically depressed group and a non-depressed control group as they performed a finger tapping task and either a simultaneous automatic or a relatively attention-demanding cognitive task, it was possible to address the issue of depression-related decreases in processing capacity. The proportional change in tapping rate, in the dual-task condition, relative to the single-task condition, served as an indicator of the resources necessary to perform the cognitive task. By comparing responsiveness to a task emphasis manipulation, designed to shift priority from a manual to a cognitive task, it was possible to address the issue of resource allocation. Finally, by comparing left- and right-hand decrement scores during simultaneous performance of either a verbal or a spatial task, it was possible to address the issue of hemispheric specialization. The results do not provide strong support for the theory of a decrease in central capacity in major depression. Instead, the findings are suggestive of a capacity limitation specific to processing spatial information. As such, the findings are more consistent with a multiple resource model of attention. In addition, the results offer some support for the model of impaired allocation of attentional resources in response to task demands. Finally, the results are suggestive of atypical hemispheric involvement when processing information in the depressed state.