Basic EEG processing and transformation

This pipeline allows you to re-reference and do high-pass filtering of your selected EEG data recordings. It also allows you to specify the frequency bands that you want to calculate.

Slew limit

You can set a slew rate limit to control the EEG signals between successive samples, up to a maximum value. Large voltage step changes from one sample to the next sometimes occur due to electrostatic discharge from the subject (participant), headset movements, or other artifacts. The effect of voltage step changes on filtered signals, and fast Fourier transform (FFT) epochs can artificially persist for a long time after the event. Setting a maximum slew rate limits the extent of step changes and reduces its impact without significantly affecting the EEG signal components.

The default slew rate in Analyzer is 30 microvolts. However, you can enter any positive value here.

Referencing

The data processed by Analyzer can be referenced to an aggregate of all the data selected. The available aggregate functions are:

• Mean

• Median

• Interquartile mean

• None (deactivates re-referencing)

Filter Coefficients

We recommend using default values for second order high-pass filter of 3dB at 0.5Hz which have been set for you. If you are experienced with filter coefficients you can change the values.

Epoch

In order to calculate the power in each frequency band (see below), the data is divided into ‘Epochs’. A Fourier transform is applied to each Epoch to calculate the power at each frequency. You can change the length of the Epoch window (in samples where the number of samples must be a power of 2) and the sliding window step size (the number of samples the data window is moved to form each successive Epoch).

Band frequencies

You can add as many frequency bands to your Analyzer as you want. You can also remove frequency bands that you do not need.

The limits of the frequency bands must be between 0 (lowest) and 64 (highest) Hz.

Once you have set the values for Basic EEG processing and band power transformation, click on the Start button. Analyzer will then process your selected data recordings.

Results

While your data is processing, the job management page will open. You can download your results file when the job is complete.

To understand details of the FFT implemented in EmotivPRO Analyzer please view the Band Power calculation section and for details of the fields in your .csv outputs please see the csv outputs section.