Reported are preliminary findings from analyses of cross-sectional and longitudinal reaction time data collected on 865 male and 453 female volunteers who ranged in age from 20 to 96 years. Evident in both simple and disjunctive reaction time measures was a consistent slowing with age. In nearly all cases, males were faster than females but gender differences were negligible for the simple reaction time (SRT) compared to disjunctive reaction time (DRT). Repeated testing within subjects over 2–8 years also showed age-related slowing across decades. Cross-sectional studies have been criticized for overestimating the actual age-related slowing found in longitudinal analysis. However, this was not the case in the present research. Similar effects were observed in analyses of data from all subjects on their first visit (n = 1318 subjects) compared to data from all subjects over all of their visits (n = 3855 subject visits) compared to data from only those subjects across decades who were tested repeatedly over at least 8 years (n = 314 subjects X 5 visits = 1570 subject visits). Findings from this research have human factors implications for task design, personnel selection, performance prediction, accident analysis, human tests and measurements, and demographic norms, to mention a few.
From 1973 to 1989, 1318 subjects ranging in age from 20 to 96 years completed auditory reaction time (RT) tasks as part of the extensive test battery of the Baltimore Longitudinal Study of Aging. In addition to central tendency, higher moments of reaction time frequency distributions (variability and skewness) were analyzed to (1) determine changes in the shape of the frequency distribution not revealed by analysis of central tendency alone, which could explain a portion of the slowing effect, and (2) examine differences in cross-sectional and longitudinal approaches. Cross-sectional results revealed significant age increases for median simple reaction time (SRT) and median disjunctive reaction time (DRT), as well as SRT and DRT variance. Males were significantly faster and less variable than females for both SRT and DRT tasks. SRT distributions were much more positively skewed than DRT distributions, and DRT distributions became more positively skewed with age. Increased variability appears to account for a sizable portion of the age-related performance slowing. Longitudinal analyses produced slightly different results, the most distinctive being the fading of age and sex differences over longer periods of time for median RT, variance, and skewness. Findings from this research have human factors implications for task design, personnel selection, accident analysis, and demographic norms.
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