The relationship between psychometric intelligence and the speed of information processing in normal, learning disabled, and brain-injured adults

A number of reaction time (RT) paradigms have been utilized to investigate the relationship between speed of information processing and measures of mental ability. In order to test the functionality of a relationship, however, the relationship should hold across a variety of subject populations. Noticeably absent from RT literature are two naturally occurring groups of learning disabled (LD) and brain injured (BI) adults. Thus, the intent of this study was to extend RT research and examine further the RT X g relationship. By using LD and BI community college students, who possess average intelligence, but yet are cognitively and functionally impaired, the hypothesis that the correlation between RT and mental ability stem from a shared biological substrate can be uniquely studied.; Employing the Posner and Sternberg paradigms, choice reaction time data were obtained on 30 normal, 30 LD, and 30 BI subjects, and compared to scores on the Slosson Intelligence Test (SIT) and Gc/Gf Sampler. The findings revealed that certain chronometric variables (i.e., mean, median, and intraindividual variability) produced low-to-moderate correlations with measures of mental ability, especially SIQ and Gc, across groups. In addition, the two disabled groups were determined to be significantly slower on the Sternberg and Posner RT tasks than the normal subjects. Unlike Gc and SIQ, Gf was found to be largely unrelated across groups to RT and movement time (MT) parameters. The observed results may be attributed, in part, to group differences in attention and arousal, deployment of cognitive strategies and strategy automatization, and in motivation. As such, a purely biological explanation of the results was rejected. Future research should focus on the intrapersonal characteristics which may influence the RT X g relationship.