General slowing of information-processing by persons with mental retardation.

On measures of speeded performance, persons with mental retardation typically respond more slowly than do those without mental retardation. A review of 45 published studies yielded 518 pairs of response times (RTs) in which each pair consisted of a mean RT for a group of persons with mental retardation for an experimental condition and the corresponding mean RT for a group of persons without mental retardation. The primary result was that RTs of individuals with mental retardation increased linearly as a function of RTs for persons without mental retardation in corresponding conditions. These results are consistent with the view that differences in processing speed between persons with and without mental retardation reflect some general (i.e., nontask specific) component of cognitive processing. Possible candidates for the general component were discussed.