Focused attention can be compromised by the neurodegenerative processes associated with both healthy aging and Parkinson's disease (PD). Deficits in ignoring distractors with reflexive or overlearned response links have been attributed to impaired inhibition. The current research assessed whether similar deficits occur for distractors with recently learned arbitrary response associations, for which sensorimotor transformations are far less automatic and therefore considerably easier to resist. We used a selective attention task that evaluated distractibility and the use of distractor inhibition within the same context. The task involved stimuli that were arbitrarily assigned to responses based on a rule learned during the testing session. Performance showed that distraction increased with both healthy aging and PD. Moreover, these increases in distraction were accompanied by decreases in overt evidence of distractor inhibition, which appear to reflect at least in part a failure of reactive inhibition. Comparison of the deficits in the two groups indicates that the key difference reflects severity, rather than distinct symptoms, suggesting that they stem from neural changes associated with both aging and PD. These results demonstrate that aging- and PD-related hyper-distractibility and impaired inhibition during focused attention affect stimuli without prepotent response links, which implicates dopaminergic networks in the strategic control of arbitrary visuomotor transformations.
Impaired visual attention is a major source of disability that adversely affects daily activities in both neurologically healthy aging populations (e.g., Anstey, Wood, Lord, & Walker, 2005; Hoffman, McDowd, Atchley, & Dubinsky, 2005; Richardson & Marottoli, 2003) and in patients with Parkinson's disease (PD, e.g., Stolwyk, Charlton, Triggs, Iansek, & Bradshaw, 2006; Uc et al., 2005 and Uc et al., 2007). For example, recent research in older adults indicates that safe driving performance can be predicted by the efficacy of inhibition during a visual attention task (Bedard et al., 2006). Despite the importance of understanding the breakdown of focused attention with advancing age and PD, a number of questions remain regarding the stimulus conditions that lead to hyper-distractibility and the deficient attentional mechanisms involved. In addition, while a number of studies have reported similar selective attention deficits associated with advancing age and PD, because few studies have assessed both, comparisons have had to be made across experiments. Thus, it remains unclear whether advancing age and PD cause distinct symptoms. Overlap in the neurological changes that occur with advancing age and PD could potentially account for common changes in selective attention. In particular, dopaminergic deficits arise with both and have been linked to executive functions, including selective attention (Kaasinen & Rinne, 2002; Volkow et al., 1998).
The data from each group (young adults, elderly adults, and elderly adults with PD) were first analyzed separately in order to establish the effects for each group (see Table 2 and Table 3, and Fig. 2 for a summary of the data from each group). We then compared the young adults to the elderly adults in order to determine whether any age-specific changes in performance occurred, and the elderly adults to the Parkinson's patients in order to determine whether any PD-specific changes in performance occurred. We calculated medians, instead of means, in an effort to reduce the influence of outliers, which can be especially problematic in patient data.
