Carr, Renee (2009) The effects of modulating temporal separation and distractor identity on distractor interference in an older population sample. PhD thesis, Victoria University.

Abstract

The phenomenon of distractor interference indicates that information not relevant to the goal is processed and has an impact on goal-directed actions. Recent work in young, healthy participants indicates that distractors presented simultaneously and also 200ms prior to targets have a significant, though attenuated, impact on responses to targets (Kritikos, McNeill & Pavlis 2008; Watson & Humphreys 1998). Beyond this interval, interference starts to diminish (Kritikos et al., 2008; Watson & Humphreys 1998). Incongruent distractors presented 200 ms prior to targets are associated with greater interference than neutral and congruent distractors (Kritikos et al., 2008; Watson & Humphreys 1998). These findings imply that internal representations of irrelevant information are capable of affecting subsequent responses to goals. In the current study, older participants were compared with younger participants to investigate age effects on response times and accuracy to simultaneously presented as well as temporally separated distractors at intervals at/greater than 200ms. The impact of age on response times to manipulations of distractor congruence was also investigated. Simultaneous presentation of target and distrator, as well distractors preceded by the target by 200 ms or I 000 ms, was associated with increased distractor interference for both groups. The presence of incongruent distractors led to increased distractor interference for both groups. During all conditions in both experiments the older group had significantly longer reaction times compared to younger participants and was relatively more accurate in response selection. Overall, the older group's slower response style seemed to be more advantageous, allowing them enough time to think more carefully about their responses. These findings are discussed with reference to Salthouse' s ( 1996) reduced speed of processing theory, which states that normal ageing is associated with generalized slowing of neural transmission. The finding that older participants were accurate in their responses and had no greater difficulty than younger participants in inhibiting incongruent distractors does not support Hasher and Zack's (1998) reduced inhibition theory. Despite overall slower reaction times, older participants demonstrated a preserved ability to inhibit unwanted stimuli in their responses.

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