Removal of artifacts by use of ZCA whitening. a, Complexity distribution of the Macaque Y (red bars) and Macaque L (blue bars) data, without (right) or with (left) ZCA whitening. For comparison, the mean (black dot) and standard deviation (error bar) of the complexity distribution of respective surrogate data are also shown. b, Global HSE index I_i for channels of the Macaque Y (red) and Macaque L (blue) data, plotted against the highest correlation C_i of the channels, without (left) or with (right) ZCA whitening. The inset in the right panel shows a magnified view of the same data. c, Comparison of spike train statistics of the Macaque Y (left) and Macaque L (right) data between without (x-axis) and without (y-axis) ZCA whitening. The color of dots represents the highest correlation of the respective channels without ZCA whitening, as indicated in the color bars to the right. Top: global HSE index for each channel. Middle: firing rate of spikes in each channel. Bottom: signal-to-noise ratio (SNR) of spike waveforms in each channel.