In the lower-2 α band for the ERD/ERS data a significant interaction effect between the factors of time, area and group was observed (F(24, 416) = 2.68; p < .00002). The MM group showed less lower-2 α ERD than did the other three groups. This difference was most pronounced in the frontal brain areas and less pronounced in the parieto-occipital areas. The greatest differences were observed in the first 2000 ms of problem solving.
In the upper-α band the ERD/ERS data showed a significant time by group interaction effect (F(12, 208) = 2.67; p < .022). The MM group showed upper-α ERS, whereas the other three groups showed upper-α ERD. The difference was especially pronounced for the period from 1000 to 3000 ms of problem solving (see Fig. 5).