Flanker interference at both stimulus and response levels decreases with age

When trying to identify the colour of a target, people's performance is impaired by nearby distractors of different colours. It is controversial whether these interference effects originate from competing stimuli, competing responses or from both simultaneously. These interference effects may also differ depending on a person's age. Comparisons between studies show mixed results, while differences in experimental design and data analysis complicate the interpretation. In our study, we manipulated the relative proportions of congruent and incongruent trials with respect to both stimuli and responses. Considering this aspect, we asked whether people resolve stimulus and response interference differently at different ages. 92 children (6-14 years), 25 young adults (20-43 years) and 33 older adults (60-84 years) performed a coloured version of the Eriksen flanker task. Since reaction times and errors were correlated, inverse efficiency scores were used to address speed-accuracy trade-offs between groups. Absolute interference effects were used to measure relationships with age. The results showed first, unexpectedly, that response interference was comparable between stimulus- and response-balanced conditions. Second, performance at all ages was significantly influenced both by competing stimuli and responses. Most importantly, the size of interference effects decreased with age. These findings cast some doubt on the conclusions of previous studies, and raise further questions about how cognitive control is best measured across the lifespan.