Deficits in processing speed in patients with multiple sclerosis: evidence from explicit and covert measures.

Cognitive slowing in individuals with multiple sclerosis (MS) has been documented by numerous studies employing explicitly timed measures in which speed of responding is an obvious focus of task performance. The present study examined information processing speed in MS patients and controls with a computerized battery of covertly timed as well as explicitly timed measures. The explicit measures were derived from two tests requiring rapid serial processing of visual stimuli, the Stroop Test and a Picture Naming Test. Covert measures were derived from the Rotated Figures Test, Remote Associates Test, and Tower of London, all tasks in which participants' attention was drawn toward arriving at an accurate solution, and the latency with which they arrived at these solutions was timed by the computer "behind the scenes." Significant differences in processing speed for patients and controls occurred on both types of measures, although the effect sizes were notably larger on the explicit measures.