Objective: To investigate whether spatial working memory (WM) is impaired in multiple sclerosis (MS), and, if it is, to localize impairment to specific cognitive subprocess(es). Method: In Experiment 1, MS and control participants performed computerized memory-span and visuomotor tasks. WM subprocesses were taxed by manipulating (1) the requirement to remember serial order, (2) delay duration, and (3) the presence of irrelevant stimuli during target presentation. In Experiment 2, recall and recognition tests varied the difficulty of WM retrieval. In Experiment 3, an attention-cueing task tested the ability to voluntarily and rapidly reorient attention. Results: Performance was worse for MS than for control participants in both spatial recall (Exp. 1 span: 95% CI MS = [5.11, 5.57], 95% CI Controls = [5.58, 6.03], p = .003, 1-tailed; Exp. 2 span: 95% CI MS = [4.44, 5.54], 95% CI Controls = [5.47, 6.57], p = .006, 1-tailed) and recognition (accuracy: 95% CI MS = [0.71, 0.81], 95% CI Controls = [0.79, 0.88], p = .01, 1-tailed) tests. However, there was no evidence for deficits in spatiotemporal binding, maintenance, retrieval, distractor suppression, or visuomotor processing. In contrast, MS participants were abnormally slow to reorient attention (cueing effect (ms): 95% CI MS : [90, 169], 95% CI Controls : [29, 107], p = .015, 1-tailed). Conclusions: Results suggest that, whereas spatial WM is impaired in MS, once spatial information has been adequately encoded into WM, individuals with MS are, on average, able to maintain and retrieve this information. Impoverished encoding of spatial information, however, may be due to inefficient voluntary orienting of attention
