Identity-Based Negative Priming: Individual Differences in Typical and Atypical Development
Degree GrantorUniversity of Canterbury
One means by which inhibitory control in selective attention may be studied is with the negative priming (NP) procedure. It is widely assumed that children are characterised by reduced capacity for inhibition (Diamond, 2002) and that inhibitory dysfunction is a key characteristic of children and adolescents with ADHD (Barkley, 1997). This should translate into reduced NP effects for these populations. In this dissertation, four studies using the NP procedure find no evidence for reduced inhibitory function in typical children or in adolescents with ADHD. Study 1 examined the magnitude of NP in children compared with adults. An important line of support for the idea that children suffer an inhibitory decrement has been based an empirical report suggesting that conceptual (identity or semantic) NP effects, assumed to reflect the by-product of distractor inhibition, while consistently found in adults are lacking in children (Tipper, Bourque, Anderson, & Brehaut, 1989). In Study 1, the opposite result was found. Study 2 compared NP effects between 7-year-old children and adults while replicating the respective methodologies of the only two studies to explore conceptual NP effects in developmental populations to date (Pritchard & Neumann, 2004, vs. Tipper et al., 1989) to determine the nature of the divergent results between these studies. In Study 2, it was found that distractor inhibition effects are comparable between children and adults when a NP task contains trials in which the distractor stimulus is consistently incongruent with the target stimulus, but that children may be more susceptible than adults to divide attention between target and distractor when a NP task contains a number of trials in which target selection difficulty is reduced. These are critical new findings, highlighting that reduced NP may often relate to methodological artifacts, and when considered in the light of current theories of NP, are also problematic for anti-inhibitory accounts of NP. Having distinguished more definitively the role of inhibition in developmental NP effects, Studies 3 and 4 explored whether the inhibitory process underpinning NP was implicated in young persons with ADHD. To date, evidence for NP in ADHD populations is equivocal. Study 3 found no evidence for a reduced NP effect in ADHD devoid of a corresponding diagnosis. Study 4 found that conduct and oppositional defiant disorders had the potential to confound the evaluation of NP in ADHD. Taken together, results in Studies 1 - 4 parallel very recent results in the literature on NP in older adults and adult psychopathology where presumed reductions of NP in these populations may also be accounted for by methodological artifacts (Buchner & Mayr, in press). It is concluded that NP may reflect a primitive and robust form of inhibitory processing, one that develops early and one that is often the last to deteriorate.