Stroop interference and negative priming in patients with multiple sclerosis

The experiment reported represents a preliminary assessment of the ability of multiple sclerosis (MS) patients to inhibit distracting stimuli in a selective attention task. Twenty MS and 20 matched control participants were given a card version of the Stroop colour-word interference task. Four conditions were included; neutral (strings of coloured Xs), congruent (colour and word matched), Stroop interference (colour and word conflicted) and ignored repeated (again, conflicting colour and words, but colour on trial n matched the word on trial n-1). Response times (RTs) to 30 trials in each condition were measured to the nearest second. Increased Stroop interference scores were evident for the MS patients relative to the control group. However, a negative priming effect was evident for both MS and control groups; RTs were longer for the ignored repeated condition relative to the Stroop interference condition. This suggests that both groups were able to inhibit distractors on trial n-1, and that increased Stroop interference scores, for MS patients were not due to a complete breakdown of inhibitory processing. Although negative priming effects did not differ across the groups, the possibility of a partial breakdown in inhibitory processes could not be ruled out. Other explanations for increased Stroop interference in MS patients are also briefly considered.