We conducted a 32-channel EEG and used FFT to calculate each frequency's Power-Value. Some of them are negative and I don't know how to interprete those im comparison to positive Power-values.
Kathrin Ohla
I would compute the absolute value of all data points returned by the function.
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Hüseyin Yanık
FFT gave a result in complex coordinates. Absolute value of all data points should be taken .
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Behzad Iravani
Power values are absolute values of complex numbers derived from FFT. They can not be negative unless they are contrasted to baseline or other conditions. If so then simply it means you have more power in the baseline or the other condition for that specific time/frequency bin.
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