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

BACKGROUND

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).

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Tests of information processing speed: what do people with multiple sclerosis think about them?

Reduction in information processing speed (IPS) is a key deficit in multiple sclerosis (MS). The Paced Auditory Serial Addition Test (PASAT), Symbol Digit Modalities Test (SDMT), and Computerized Test of Information Processing (CTIP) are used to measure IPS. Both the PASAT and SDMT are sensitive to deficits in IPS. The CTIP, a newer task, also shows promise. The PASAT has several limitations, and it is often perceived negatively by patients. Yet little supporting quantitative evidence of such perceptions has been presented. Therefore, in this study, subjective ratings of likeability, difficulty, and appropriateness of the PASAT, CTIP, and SDMT were obtained. Ratings were compared between MS patients and healthy controls. It was hypothesized that ratings of the PASAT would differ significantly from those of the SDMT and CTIP. The relationship between subjective ratings and objective performance was evaluated. Sixty-nine MS patients and 68 matched controls rated the three tests in terms of likeability, difficulty, and appropriateness for capturing cognitive deficits often associated with MS using a Likert scale. Both groups rated the PASAT as most difficult and least likeable. The MS group rated the PASAT and SDMT as more appropriate for measuring MS-related deficits than the CTIP. Subjects who performed better on the PASAT were more likely to rate it as easier. Ratings of the SDMT and CTIP did not vary consistently with performance. The findings lend quantitative support to the common belief that the PASAT is perceived as unpleasant. Other tests are available that are similarly sensitive to deficits in IPS and more palatable to the patient.

Processing speed versus working memory: contributions to an information-processing task in multiple sclerosis

Individuals with multiple sclerosis (MS) often experience cognitive impairments in information processing. However, the relative contributions of processing speed abilities and working memory abilities to information-processing tasks are not yet fully understood. The current study examined the extent to which processing speed and/or working memory abilities contributed to an information-processing task, the Keeping Track Task (KTT). Forty-nine individuals with MS were given tests to assess processing speed and working memory, as well as the KTT. Regression analyses indicated that in the MS group, processing speed abilities accounted for the majority of the explained variance in KTT performance. The findings suggest that processing speed plays a significant role on KTT performance in MS. Implications for cognitive rehabilitation treatments aimed at improving processing speed abilities in MS are discussed.

The role of speed versus working memory in predicting learning new information in multiple sclerosis

The most common cognitive impairments in multiple sclerosis (MS) have been documented in specific domains, including new learning and memory, working memory, and information processing speed. However, little attempt has been made to increase our understanding of their relationship to one another. While recent studies have shown that processing speed impacts new learning and memory abilities in MS, the role of working memory in this relationship has received less attention. The present study examines the relative contribution of impaired working memory versus processing speed in new learning and memory functions in MS. Participants consisted of 51 individuals with clinically definite MS. Participants completed two measures of processing speed, two measures of working memory, and two measures of episodic memory. Data were analyzed via correlational and multiple regression analysis. Results indicate that the variance in new learning abilities in this sample was primarily associated with processing speed, with working memory exerting much less of an influence. Results are discussed in terms of the role of cognitive rehabilitation of new learning and memory abilities in persons with MS.

The impact of multiple sclerosis on patients' performance on the Stroop Test: processing speed versus interference

Deficits in multiple sclerosis (MS) patients' performance on the Stroop Test have been attributed to problems with processing speed and selective attention. Data for 248 MS patients and 178 controls on all three trials of the Stroop were combined using various scoring formulas proposed for assessing processing speed, color difficulty, and interference. The greatest differences between patients and controls involved processing speed. Formulas purporting to measure interference yielded highly inconsistent results: Significant differences between groups were found on two of the most common measures but were in opposite directions. This contradiction stems from the failure of both measures to effectively control for processing speed when assessing interference. Three alternative measures, using relative, ratio, and residualized scores, offer much better indices of interference. When assessed with these alternative measures, interference increased with age, but no differences between patients and controls were found. Difficulties that MS patients have with the Stroop Test are confined to processing speed.

Examining the link between information processing speed and executive functioning in multiple sclerosis

Slowed information processing speed (IPS) is frequently reported in those with multiple sclerosis (MS), and at least 20% are compromised on some aspect of executive functioning also. However, any relationship between these two processes has not been examined. The Sternberg Memory Scanning Test, Processing Speed Index (WAIS-III), Delis Kaplan Executive Function System (D.KEFS), and Working Memory Index (WMS-III) were administered to 90 participants with MS. Their performance on the PSI was significantly below the normative scores but no deficits in memory scanning speed were evident. The initial response speed of the Sternberg and the PSI were more closely related to D.KEFS performance, particularly in timed tasks with a high cognitive demand (switching tasks). In contrast, memory scanning speed was related to working memory. This study reinforces the link between IPS and working memory in MS, and supports the suggestion that IPS is not a unitary construct.

Cognitive impairment in multiple sclerosis: evidence-based analysis and recommendations

Cognitive impairment is common in multiple sclerosis (MS), occurring at all stages of the disease, and can be a major source of vocational disability, social impairment, and impoverished quality of life. Dysfunction in free recall from long-term memory, speed of information processing, working memory, and abstract reasoning are frequently observed in MS. Despite weak correlation with disease duration and physical disability status, the degree of cognitive impairment in MS has been related to the extent of topographically specific neuronal tissue damage and loss. Additional clinical factors including disease course, fatigue, affective disturbance, and medication can impact on the degree of MS-related cognitive impairment. We suggest that the symbol digits modalities test, paced auditory serial addition task, the clock drawing test and the MS neuropsychological screening questionnaire be considered as valid and relevant screening tests for cognitive impairment in MS.

The relationship between neuropsychological measures and the Timed Instrumental Activities of Daily Living task in multiple sclerosis

Multiple sclerosis (MS) can result in cognitive deficits and a loss of functional independence. To date, little research has linked the observed cognitive and behavioral deficits in MS, especially those in the processing speed domain, to performance on tasks of everyday functioning. The present study examined the relationship between neuropsychological test performance and performance on the Timed Instrumental Activities of Daily Living task (TIADL) in individuals with MS, and in healthy controls (HCs). The TIADL is a functional measure, which assesses both accuracy and speed in one's performance of everyday activities. The MS group performed significantly worse on the TIADL relative to the HC group. Additionally, TIADL scores of individuals with MS were significantly correlated with neuropsychological measures of processing speed. TIADL scores were not, however, correlated with neuropsychological measures of verbal episodic memory or working memory. These results indicate that the impairments in processing speed may contribute to impairments in activities of everyday living in persons with MS. Multiple Sclerosis 2007; 13: 636-644. http://msj.sagepub.com

Pushing the frames of reference in traumatic brain injury rehabilitation

Cognitive rehabilitation is an empirically based field driven by multiple sources of activities and knowledge bases. Drawing on frames of reference provided by rehabilitation, neuropsychology, and rehabilitation psychology, cognitive rehabilitation has evolved to a point where studies have been generated to qualify for consideration in tables of evidence. At the center of cognitive rehabilitation is the effort to teach people to overcome or adapt to limitations. While rehabilitation has traditionally been focused on activity, a recent trend in the literature is to incorporate the individuals experience into a frame of reference for rehabilitation. Emphasizing the experience of the person in the situation fits into cognitive rehabilitation and raises the bar for rehabilitation not only in viewing rehabilitation as an activity to relieve burdens but also in terms of how rehabilitants come to grips with limitations. Dealing with limitations is an important indicator of mental health.