Topographic distribution of the average number of principle components accounting for 90% of variance.

Estimation of the variability between trials in the Ne-time window for both tasks. Blue indicates less variability between trials; red indicates more variability between trials. Beside each topography a colour legend is provided indicating the number of principle components (PCs) explaining at least 90% of variance between trials. For example having a look at the topography of the young subjects in the flanker task, one can see that at FCz about three principle components explain at least 90% of variance between trials. In older participants (left) about five principle components explain at least 90% of variance between trials. Note that in general the signal is least variable at fronto-central positions and reflects the typical Ne-topography.