Fig. 6.

The type of filter and cut-off frequency used in each study (42 studies reported the filter type and/or cut-off frequency). The upper panel shows the cut-off frequency of the band-pass filter (purple bars). The lower panel indicates the cut-off frequency of the low-pass filter (red line) and high-pass filter (green line). Shadow areas indicate the type of filters: BW, Butterworth filter; FIR, Finite Impulse Response filter. The studies which did not report the filter type are also shown (named as Others). The number in the bars or below the red (green) line indicates the order of the filter. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)