title: Diversity, dispersion and inconsistency of reaction time measures: effects of age and task complexity.
abstract: OBJECTIVE
  Performance variability of reaction time is regarded as an important parameter for cognitive functioning with aging. We investigated three types of variability, diversity (or variability between persons), dispersion (variability across trials within one task) and inconsistency (variability across testing occasions), while distinguishing between decision time and movement time and evaluating performance across comparable complexity levels.
  
  
  METHODS
  A single stratified reaction time test based on tasks with increasing complexity was used to evaluate inter- and intra-performance variability of 27 older (age 75+/-5 years) and 27 younger (age 29+/-7 years) participants, subdividing reaction time into decision and movement components.
  
  
  RESULTS
  There were consistent age and complexity differences for all variability types in our sample. When controlling for processing speed, which was slower in the older group, variability across age groups and task complexity tended to diminish and a more complex picture emerged. The elderly group showed a higher diversity of all reaction time measures, except for movement time, and a higher dispersion of decision time. Task complexity significantly affected the diversity of movement and overall reaction times and the dispersion of all reaction time measures, except for movement time.
  
  
  CONCLUSIONS
  These results highlight the importance of variability in cognitive functioning; it may be an important phenomenon for study and a useful indicator for cognitive deterioration. The reaction time test we propose is easy to use and can be applied in clinical practice.
authors.affiliation: Gerontology, Free University of Brussels (VUB), Laarbeeklaan 101, B-1090 Brussels, Belgium.
authors.forename: Ellen
authors.initials: E
authors.lastname: Gorus
authors.forename: Rudi
authors.initials: R
authors.lastname: De Raedt
authors.forename: Tony
authors.initials: T
authors.lastname: Mets
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D003071:Cognition / Q000502:physiology; D003657:Decision Making / Q000502:physiology; D005260:Female; D015577:Geriatric Assessment; D006801:Humans; D008297:Male; D011597:Psychomotor Performance / Q000502:physiology; D011930:Reaction Time / Q000502:physiology*; D015203:Reproducibility of Results; D013647:Task Performance and Analysis