title: Individual variability in speed of information processing: an index of cognitive impairment in multiple sclerosis.
abstract: OBJECTIVE
  The principal cognitive domain impacted by multiple sclerosis (MS) appears to be information processing speed. Studies have documented mean differences between MS patients and healthy controls on numerous measures of information processing speed, but the present study is one of the first to examine individual variability (i.e., inconsistency) in processing speed.
  
  
  METHODS
  Thirty-nine patients with relapsing-remitting or secondary progressive MS and 32 healthy controls completed a series of reaction time (RT) tests, the Stroop Test, and the Rey Auditory Verbal Learning Test. In addition to mean differences, appropriate measures of individual variability (i.e., coefficients of variability) were obtained for the tests yielding response times.
  
  
  RESULTS
  MS patients performed more poorly on all response time measures, responding more slowly and with greater inconsistency than controls. Logistic regression analyses showed that inconsistency measures contributed independently to the discrimination between groups beyond that resulting from measures of mean processing speed. The so-called "complexity effect" was also demonstrated; greater between-groups differences on both mean RTs and inconsistency generally occurred on tasks placing greater demand on central executive resources.
  
  
  CONCLUSIONS
  Processing speed in MS patients is characterized by greater individual variability as well as overall declines. This variability should be examined further in relation to neuroimaging indices of MS.
authors.affiliation: University of Kansas, Lawrence, KS, USA.
authors.forename: Angela M
authors.initials: AM
authors.lastname: Bodling
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Denney
authors.forename: Sharon G
authors.initials: SG
authors.lastname: Lynch
mesh_terms: D000328:Adult; D002755:Choice Behavior / Q000502:physiology; D003072:Cognition Disorders / Q000175:diagnosis* / Q000209:etiology*; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D007206:Individuality; D016015:Logistic Models; D008297:Male; D008606:Mental Processes / Q000502:physiology*; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000150:complications*; D009483:Neuropsychological Tests; D011597:Psychomotor Performance; D011930:Reaction Time / Q000502:physiology; D014706:Verbal Learning / Q000502:physiology