A process-specific approach in the study of normal aging deficits in cognitive control: What deteriorates with age?

Bearing in mind that cognitive control is a complex function that includes several processes, it is not clear exactly which ones deteriorate with age. In fact, controversial results have been found. For example, some studies indicate that age-related deficits are observed in proactive and not in reactive control, others show that it is reactive control that is impaired and not proactive control, and some studies find no deficits at all (e.g., Kopp, Lange, Howe, & Wessel, 2014; Xiang et al., 2016). One possible reason is that the contribution of different processes to the deterioration of cognitive control was investigated separately, i.e., without testing all processes within the same paradigm. Therefore, the main goal of the present experiment was to study the impact of normal aging on several processes related to cognitive control within the same task, which included both Simon and Spatial Stroop trials. The study focused on the following processes: generation of conflict measured by automatic response capture (i.e., stronger task-irrelevant information processing compared to task-relevant information processing); conflict detection; and control implementation (which can be reactive control, both within trials and across trials, and proactive control, as a task-set strategy). The results showed larger automatic response capture for older adults when facing a stimulus-response conflict (Simon) but not a stimulus-stimulus conflict (Spatial Stroop). Similarly, older adults also showed larger detection effects for both conflicts. However, regarding control implementation, they only showed difficulties in inhibiting the early automatic response capture (within-trial reactive control) but not reactive control across trials or proactive control. In conclusion, it seems that older adults are more affected by the presence of task-irrelevant information, especially when it comes to resolving stimulus-response conflict. However, they showed no impairments in their ability to implement cognitive control both across trials and as a task-set strategy.

Gradual proportion congruent effects in the absence of sequential congruent effects.

In perceptual filtering tasks, congruency effects vary as a function of proportion congruent (PC), with smaller congruency effects when congruent trials are rare than when they are frequent. This effect is typically larger with extreme differences between high and low proportion congruent conditions (e.g., 80% congruent-20% incongruent) than with intermediate differences (e.g., 60% congruent-40% incongruent; Logan & Zbofroff, 1979; Blais & Bunge, 2010). Some authors have claimed that both PC effects can be explained in terms of the same reactive cognitive control mechanism that is responsible for sequential congruency (SC) effects (e.g., Botvinick, Braver, Barch, Carter, & Cohen, 2001). In fact, in most previous studies there was a systematic confounding between proportion congruent and the proportion of transitions involving an incongruent trial followed by another incongruent trial. In the present study we eliminated this confound and tested directly whether PC effects can still be measured in the absence of SC effects. Once confirmed, we studied the properties of this pure form of PC effect, in particular whether it is conflict-type specific or general, and whether it decreases gradually as a function of changes in proportion congruency (80% vs. 70% vs. 60%). Our results showed significant PC effects in the absence of SC effects, which replicates our previous findings (Torres-Quesada, Milliken, Lupiáñez, & Funes, 2014), and PC effects that can be conflict-type general or specific, depending on the nature of conflict type where they were produced. Importantly, the congruency effect was modulated by the level of proportion congruent, decreasing systematically as the absolute percentage of incongruent trials decreases.