Miyake, Friedman, Emerson, Witzki, Howerter and Wager (2000) have argued that the central executive is fractionated consisting of at least three separable component processes: updating, shifting, and inhibition. The Wisconsin Card Sort Test, random letter generation, Brooks spatial sequences, reading and computation span, word fluency, and a measure of dual task performance were administered to 95 individuals aged between 20 and 81, average age 41.89. The executive measures were factor analyzed, using the oblique rotation method, yielding four factors. The factor structure obtained was broadly consistent with Miyake et al's. However, an additional factor, the only one not to show a significant performance decline with age, was also obtained and was believed to reflect the efficiency of access to long-term memory.

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Gilinsky and Judd (1994) demonstrated that age-related impairment in syllogistic reasoning was in part due to reduced working-memory capacity. A total of 30 older (average age 66 years) and 34 younger persons (average age 24 years) were tested on syllogisms of various types as well as on other measures. Syllogistic reasoning was significantly correlated with education, processing speed, word span, and word fluency. Correlations with visuo-spatial processing and random letter generation were just short of significance. Syllogistic reasoning performance declined with age, although the deficit was no longer statistically significant following control for age-related differences in information-processing speed. On the other hand the inclusion of word fluency as an additional covariate boosted the apparent age effect, returning it to statistical significance. Thus it is possible that cognitive processes outside of working memory might underpin at least part of the apparent age deficit. This possibility is evaluated in the light of neuropsychological evidence implicating the prefrontal cortex in both the processing of syllogisms and more generally in cognitive ageing.

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