EEG and Brain Connectivity: A Tutorial - Bio-Medical Instruments, Inc.

Figure 20 below is the same as figure 19, but contains the standard
deviations. A 500 msec. averaging delay = 0.15 standard deviation while
1,000 msec = 0.1 standard deviation. This figure shows that the choice of
a 500 millisecond integration delay yields a reasonably stable estimate of
coherence when using EEG biofeedback but that shorter intervals, such as
125 msec or 250 msec produce high inflation and high standard deviations
and will not provide a valid “feedback” signal and thus less averaging will
likely reduce neurotherapy efficacy.
Figure 20. Standard deviations of coherence (y-axis) and the integration
window size in milliseconds (x-axis). Top left is sample rate = 512Hz, top
right sample rate = 256 Hz, bottom left sample rate = 128 Hz and bottom left
sample rate = 64 Hz.
EEG phase is not the same as coherence and it can be computed
instantaneously without averaging. Phase reset curves without averaging
provide a detailed picture of the phase stability between coupled oscillators.