Abstract
BACKGROUND: Several studies have shown that Stroop interference is stronger in children than in adults. However, in a standard Stroop paradigm, stimulus interference and response interference are confounded. The purpose of the present study was to determine whether interference at the stimulus level and the response level are subject to distinct maturational patterns across childhood. Three groups of children (6-7 year-olds, 8-9 year-olds, and 10-12 year-olds) and a group of adults performed a manual Color-Object Stroop designed to disentangle stimulus interference and response interference. This was accomplished by comparing three trial types. In congruent (C) trials there was no interference. In stimulus incongruent (SI) trials there was only stimulus interference. In response incongruent (RI) trials there was stimulus interference and response interference. Stimulus interference and response interference were measured by a comparison of SI with C, and RI with SI trials, respectively. Event-related potentials (ERPs) were measured to study the temporal dynamics of these processes of interference. RESULTS: There was no behavioral evidence for stimulus interference in any of the groups, but in 6-7 year-old children ERPs in the SI condition in comparison with the C condition showed an occipital P1-reduction (80-140 ms) and a widely distributed amplitude enhancement of a negative component followed by an amplitude reduction of a positive component (400-560 ms). For response interference, all groups showed a comparable reaction time (RT) delay, but children made more errors than adults. ERPs in the RI condition in comparison with the SI condition showed an amplitude reduction of a positive component over lateral parietal (-occipital) sites in 10-12 year-olds and adults (300-540 ms), and a widely distributed amplitude enhancement of a positive component in all age groups (680-960 ms). The size of the enhancement correlated positively with the RT response interference effect. CONCLUSION: Although processes of stimulus interference control as measured with the color-object Stroop task seem to reach mature levels relatively early in childhood (6-7 years), development of response interference control appears to continue into late adolescence as 10-12 year-olds were still more susceptible to errors of response interference than adults.