The effects of conflict strength and ageing on cognitive control

Electronic version excludes material for which permission has not been granted by the rights holderIn this thesis, I investigated effects of conflict strength and ageing on cognitive control. Conflict strength was manipulated in the Eriksen flanker task using two different approaches: 1. independent variation of flanker and target contrast; 2. manipulation of stimulus onset asynchrony (SOA). Reducing flanker contrast relative to target contrast decreased conflict strength, as shown by a reduction in compatibility effects, when contrast conditions were presented in a randomized fashion but not when they were presented block-wise. An SOA of 100 ms did lead to increased compatibility effects compared to SOAs of 0 ms and 200 ms. Effects of conflict appear to be reflected in the N2 component of the ERP. Although priming played a crucial role in the emergence of the sequential adjustment effect, conflict strength also influenced this effect to a certain degree, supporting the claim that sequential adjustments represent an adaptation of cognitive control. Post-error slowing and error-related ERP components, on the other hand, were not affected by the conflict manipulations, suggesting that errors cannot be explained in terms of conflict processing. Effects of ageing on cognitive control were investigated in a group of middle-aged participants. Although physiological indicators of conflict and error processing were compromised in this age group and overall response times were increased, compatibility, sequential adjustment, and post-error slowing effects were of comparable size as in young adults. These findings suggest that participants could successfully compensate for age-related physiological changes at this early stage of ageing. In conclusion, the research presented in this thesis provided important information to extend our knowledge of factors influencing cognitive control processes

Weaker error signals do not reduce the effectiveness of post-error adjustments:Comparing error processing in young and middle-aged adults

In this study we investigated age-related differences in error processing, comparing performance measures and physiological indicators of error processing of middle-aged (41–59 years) and young (18–31 years) adults using a version of the Eriksen flanker task. Although middle-aged participants were overall slower, both groups showed a comparable decrease in reaction time on error trials as well as slower and more accurate post-error performance. Despite the preserved error speeding and post-error slowing effects, we found an amplitude reduction in the Ne/ERN, contradicting the existence of a direct relationship between the amplitude of this component and post-error adjustments. This was further supported by the lack of significant correlations between the single-trial Ne/ERN amplitude and error-related reaction times. The single-trial Ne/ERN distribution showed a reduced variance for middle-aged compared to young participants, suggesting that weaker overall error signals rather than lapses in error detection are responsible for the observed Ne/ERN amplitude reductions. However, we argue that the signal still reached the necessary threshold to trigger normal post-error adjustments. Finally, the early Pe showed a reduction in amplitude and an increase in latency for middle-aged compared to young adults. Together, the findings suggest clear signs of a physiological decline in error processing at an earlier age than previously known, but these changes do not yet affect implementation of adaptive behavioral changes in middle-aged participants

Mean response times of the high-proficiency and the low-proficiency group for correct responses as a function of response direction and stimulus.

<p>Error bars represent 95% confidence intervals [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0193349#pone.0193349.ref067" target="_blank">67</a>].</p

Individual comparisons of the error rates for compatible and incompatible trials per language group.

<p>Individual comparisons of the error rates for compatible and incompatible trials per language group.</p

Single comparisons of the RTs for compatible and incompatible trials per proficiency group.

<p>Single comparisons of the RTs for compatible and incompatible trials per proficiency group.</p

Single comparisons of the error rates for compatible and incompatible trials per proficiency group.

<p>Single comparisons of the error rates for compatible and incompatible trials per proficiency group.</p

Descriptive information about class level, school type, and bilingualism [57] of our participants.

<p>Descriptive information about class level, school type, and bilingualism [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0193349#pone.0193349.ref057" target="_blank">57</a>] of our participants.</p

Mean response times for correct responses as a function of response direction and stimulus for the different language groups separately.

<p>Error bars represent 95% confidence intervals [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0193349#pone.0193349.ref067" target="_blank">67</a>].</p

Example item from the used adaptation of the TRPS [45].

<p>The child is expected to fill in the preposition <i>über</i> (<i>Der Wecker steht über dem Bett / The alarm clock is standing above the bed)</i>.</p

Average scores on language tests, self-reported language contact/use, and socio-economic status of the language groups.

<p>Average scores on language tests, self-reported language contact/use, and socio-economic status of the language groups.</p