Cognitive control operations involved in switching tasks, and deficits associated with aging and Parkinson's disease




Woodward, Todd Stephen

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The purpose of this investigation was to identify the cognitive control operations involved in task switching, and to apply this understanding to a theoretical account of the qualitatively different task-switching deficits associated with aging versus Parkinson's disease (PD). Participants in young (N = 33), elderly (N = 34) and PD ( N = 34) samples switched between color naming and word reading in response to incongruent, neutral, or congruent Stroop stimuli and vocal response time (RT) was recorded. The results suggested that executive processes involved in switching selective attention between object attributes determined a substantial portion of task-switching RT costs. More specifically, these component control processes were identified as: (a) shifting selective attention from the stimulus dimension just attended to on the previous response to the now-relevant stimulus dimension (SHIFT), and (b) a preventative operation characterized by the partial inhibition of selective attention to the now-relevant stimulus dimension, carried out when the probability is high that the now-relevant dimension must be ignored on a future response (MODERATE). A multilayer, linear, parallel distributed processing (PDP) model was presented to demonstrate how these cognitive processes may be implemented by the cognitive system, and how these findings relate to the executive function concepts of the Supervisory Attentional System (SAS) and Contention Scheduling (CS). In addition, a cost associated with responding to the first member of a stimulus pair or triplet was also identified (FIRST); however, this operation appeared to function independently from the executive control operations involved in switching tasks (i.e., FIRST was also present for task repetition trials). Finally, a number of two-way interactions between these three main effects (SHIFT, MODERATE and FIRST) accounted for unique variance in task-switching RTs, such that RT was increased when these effects co-occurred. In the neuropsychological investigation it was demonstrated that the SHIFT and MODERATE effects were significantly greater for an elderly sample compared to a young sample, resulting in an increase in task-switching RT. This deficit was attributed to an inefficient shifts of selective attention. Conversely, PD did not necessarily affect the SHIFT and MODERATE operations, when compared to age-matched controls; however, the disease was associated with difficulty overcoming Stroop interference while switching tasks. This deficit was interpreted as affecting the SHIFT operation under the most taxing conditions, attributable to a central resource deficit in PD. In contrast, no between-group differences on the effect FIRST were observed.



Cognitive psychology, Aging, Parkinson's disease