Center of gravity for frequency. (a) Individual frequency values of maximum coherence (centre of gravity) calculated for the whole range study (15–45 Hz). Each subject is represented by a number. Filled circles and square: individual values and their mean for the SF condition. Small empty circles and square: values and mean for the sD condition. Large empty circles and square: values and mean for the lD condition. The beta-range (15–45 Hz) is marked in light grey, the gamma-range (30–45 Hz) in dark grey. Note that the frequency values for the both dynamic conditions are systematically higher than for the static condition, but there are no differences of the frequency values between both dynamic conditions.