Age-related slowing in semantic information processing speed: an individual differences analysis.

This study investigated age differences in the speed of processing semantic information. Thirty young adults and 25 older adults completed five reaction time (RT) tasks: simple RT, two-choice RT to nonverbal stimuli, and three tasks measuring speed of making semantic judgments. The data were used to examine individual differences in RT factors, estimated by means of confirmatory factor analysis. All three semantic RT tasks loaded on a single semantic RT factor, with equivalent factor loadings for young and older participants, indicating that the three tasks were measuring a common factor of semantic memory access speed (SMA). The two groups differed significantly in the covariances among the RT factors; most important, the SMA factor had a higher correlation with a two-choice RT factor in the older group. This finding is taken as support of individual differences in age-related slowing on these two RT factors.