The symbol digit modalities test and the paced auditory serial addition test involve more than processing speed

• Published in: Multiple sclerosis and related disorders 2022-12, Vol.68, p.104229-104229, Article 104229
• Main Authors: Berrigan, Lindsay I., LeFevre, Jo-Anne, Rees, Laura M., Berard, Jason A., Francis, Ashley, Freedman, Mark S., Walker, Lisa A.S.
• Format: Article
• Language: English
• Subjects: Adult; Cognition; Cognition Disorders - diagnosis; Humans; Information processing speed; Multiple sclerosis; Multiple Sclerosis - complications; Multiple Sclerosis - diagnosis; Multiple Sclerosis, Relapsing-Remitting - complications; Multiple Sclerosis, Relapsing-Remitting - diagnosis; Neuropsychological Tests; Neuropsychology; Paced auditory serial addition test; Processing Speed; Symbol digit modalities test
• ISSN: 2211-0348; 2211-0356
• DOI: 10.1016/j.msard.2022.104229

•Processing speed, working memory, and learning were associated with the SDMT.•Processing speed and working memory were associated with the PASAT.•The findings support a multifactorial interpretation of the SDMT and PASAT.•Their multifactorial nature supports their usefulness as screening measures.•This also prevents them from identifying the specific cognitive functions affected. Slowed processing speed is the most frequently reported cognitive deficit for people with multiple sclerosis (MS). However, measures used to assess processing speed may also recruit other cognitive abilities. The present objective was to determine the contributions of different cognitive functions to performance on two commonly used processing speed measures: the Symbol Digit Modalities Test (SDMT) and the Paced Auditory Serial Addition Test (PASAT). Adults with relapsing-remitting MS (n = 70) and controls (n = 72) completed the SDMT, PASAT, and multiple measures assessing processing speed, working memory, and learning. Hierarchical regression analyses were used to examine the contributions of MS, processing speed, working memory, learning, and all possible interactions among factors to SDMT and PASAT scores. Processing speed and working memory generally contributed to performance on the SDMT and PASAT, with learning additionally contributing to SDMT performance. However, significant interactions revealed processing speed did not influence PASAT performance for individuals with high working memory ability whereas processing speed became increasingly more important as working memory declined to average and low levels. Further, processing speed was associated with SDMT performance for patients with MS but not controls. These findings support a multifactorial interpretation of the SDMT and PASAT, which facilitates their usefulness as screening measures for cognitive decline but prevents them from identifying which specific cognitive functions are affected.