The present study investigated effects of cognitive aging on conflict resolution (the ability to suppress prepotent and distracting, irrelevant information) and conflict adaptation (the adjustment of conflict resolution based on previously experienced conflict level). In addition, it aimed at investigating whether Cognitive Reserve (CR) and intelligence play a compensatory role against age-related deficits in both factors. A color-word Stroop task with no feature repetitions (i.e., neither the word nor the color was repeated in two subsequent trials) was administered to 23 older adults with no dimentia (65-79 years old) and 22 younger controls (18-34 years old), in addition to measures of intelligence and CR. Older adults' performance was characterized by general slowing. However, response slowing inversely correlated with intelligence, education, and a cognitive-reserve index. The Stroop effect (i.e., response-time (RT) difference between incongruent and congruent conditions) was larger in older adults than in younger controls, and in the older group only, it negatively correlated with verbal IQ. With this feature-repetitions-free Stroop task, we confirmed the presence of some conflict adaptation effects, which, however, were spared by aging. Altogether, these findings show that older adults can cope better with age-related impairment in verbal interference resolution, if they have enough intelligence resources in a related (verbal) domain, whereas CR plays a role in general performance speed only. We therefore suggest that general and specific accounts of cognitive aging may apply to different processing stages, which are influenced by partially different compensatory factors.

Responding to the color of a word is slower and less accurate if the word refers to a different color (incongruent condition) than if it refers to the same color (congruent condition). This phenomenon, known as the Stroop effect, is modulated by sequential effects: it is bigger when the current trial is preceded by a congruent condition than by an incongruent one in the previous trial. Whether this phenomenon is due to priming mechanisms or to cognitive control is still debated. To disentangle the contribution of priming with respect to conflict adaptation mechanisms in determining sequential effects, two experiments were designed here with a four-alternative forced choice (4-AFC) Stroop task: in the first one only trials with complete alternations of features were used, while in the second experiment all possible types of repetitions were presented. Both response times (RTs) and errors were evaluated. Conflict adaptation effects on RTs were limited to congruent trials and were exclusively due to priming: they disappeared in the priming-free experiment and, in the second experiment, they occurred in sequences with feature repetitions but not in complete alternation sequences. Error results, instead, support the presence of conflict adaptation effects in incongruent trials. In priming-free sequences (experiment 1 and complete alternation sequences of experiment 2) with incongruent previous trials there was no error Stroop effect, while this effect was significant with congruent previous trials. These results indicate that cognitive control may modulate performance above and beyond priming effects.

Several studies support the existence of a specific age-related difficulty in suppressing potentially distracting information. The aim of the present study is to investigate whether spatial conflict resolution is selectively affected by aging. The way aging affects individuals could be modulated by many factors determined by the socieconomic status: we investigated whether factors such as cognitive reserve (CR) and years of education may play a compensatory role against age-related deficits in the spatial domain. A spatial Stroop task with no feature repetitions was administered to a sample of 17 non-demented older adults (69–79 years-old) and 18 younger controls (18–34 years-old) matched for gender and years of education. The two age groups were also administered with measures of intelligence and CR. The overall spatial Stroop effect did not differ according to age, neither for speed nor for accuracy. The two age groups equally showed sequential effects for congruent trials: reduced response times (RTs) if another congruent trial preceded them, and accuracy at ceiling. For incongruent trials, older adults, but not younger controls, were influenced by congruency of trialn−1, since RTs increased with preceding congruent trials. Interestingly, such an age-related modulation negatively correlated with CR. These findings suggest that spatial conflict resolution in aging is predominantly affected by general slowing, rather than by a more specific deficit. However, a high level of CR seems to play a compensatory role for both factors.

An important aspect of cognitive control is the ability to overcome interference, by boosting the processing of task-relevant information while suppressing the irrelevant information. This ability is affected by the progressive cognitive decline observed in aging. The aims of this study were to shed light on the neural spectral dynamics involved in interference control and to investigate agedependent differences in these dynamics. For these reasons two samples of participants of different ages (23 younger and 20 older adults, age range = [18 35] and [66 82], respectively) were recruited and administered a spatial Stroop task while recording electroencephalographic activity. Scalp-and source-based time-frequency analyses revealed a main role of theta and beta frequencies in interference control. Specifically, for the theta band, we found age-dependent differences both for early event-related spectral perturbation (ERSP) Stroop effects at the source level -which involved dorsomedial and dorsolateral prefrontal cortices -and for related brain-behaviour correlations. This ERSP Stroop effect in theta was greatly reduced in magnitude in the older group and, differently from what observed in younger participants, it was not correlated with behavioural performance.These results suggest an age-dependent impairment of the theta-related mechanism signalling the need of cognitive control, in line with existing findings. We also found age-related differences in ERSP and source spectral activity involving beta frequencies. Indeed, younger participants showed a specific ERSP Stroop effect in beta -with the main involvement of left prefrontal cortex -whereas the pattern of older participants was delayed in time and spread bilaterally over the scalp. This study shows clear age-related differences in the neural spectral correlates of cognitive control. These findings open new questions about the causal involvement of specific oscillations in different cognitive processes and may inspire future interventions against age-related cognitive decline.

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