Do developmental changes in inhibitory ability underpin developmental changes in intelligence?

Fiona Michel

Research output: ThesisMaster's Thesis

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[Truncated abstract] Intelligence in children increases with age until adult levels of performance are achieved. Dempster (1991) proposed that developmental changes in inhibitory processes underpin these changes in the development of intelligence. The evidence Dempster presented to support this thesis typically takes the form of noting changes in inhibitory performance that occur in the same time frame as changes in psychometric intelligence (Dempster, 1991, 1992, 1993; Dempster & Corkill, 1999). He also provides correlational evidence from studies in which intelligence scores are correlated with various inhibitory measures. One problem with much of the evidence presented by Dempster is that it does not distinguish between developmental and individual differences in inhibition and/or intelligence. Developmental differences are differences in performance between children at different ages. Individual differences are differences in performance between children of the same age. The majority of evidence Dempster provides concerns individual differences in inhibition and the relationship of these differences to intelligence rather than the relationship of any developmental differences to intelligence. Anderson (1987) suggests that the processes underpinning these two types of differences are not necessarily the same. For example, individual differences may be related to speed of processing, while developmental differences may be related to changes in inhibitory ability. Therefore, a more accurate test of Dempster’s thesis is to assess whether developmental changes in inhibition are related to developmental changes in intelligence, rather than whether individual differences in inhibition are related to intelligence. This was the primary goal of this thesis. A secondary goal was to address whether or not any developmental changes seen were primarily due to changes in inhibition or could be accounted for by changes in speed of processing. Measures which utilise difference score reaction time (RT) measures as inhibitory indices such as the stroop task do not typically account for this potential confound. A number of researchers have addressed this problem of difference score measures and proposed alternative analytic techniques (Christ, White, Mandernach, & Keys, 2001; Christ, White, Brunstrom, & Abrams, 2003; Faust, Balota, Spieler & Ferraro, 1999). Each inhibitory measure used in the current study will attempt to control for group and individual speed differences, either by utilising one of these alternative techniques or using regression analysis to identify the contribution of speed to the developmental shift in intelligence.
Original languageEnglish
Publication statusUnpublished - 2006


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