Analyzing Alpha Brain Waves

[belaslim3]

Hey James,

I've been using your Muse Monitor program to analyze alpha brain waves for my science fair research project. I'm studying the effect of different meditation apps on alpha waves. I used Excel to graph the CSV data, and ran the macro which has been very helpful for my project so far. Since in my project I am measuring the effectiveness of different meditation apps, I believe I need to look at the Average Alpha values for the each session. I have attached one of the files to this post as an example.
On the Muse Monitor website on the Graphing Online tab, I uploaded this file and saw the "Ave Alpha" meter read "84.116".
Three questions:
1) Is this the average alpha wave value for the whole recording?
2) What unit is this number in?
3) How can I calculate, or how can I get to, this number in Excel after having run the macro?

Thanks,
Bela

[James]

#1 - Yes
#2 - Bels
#3 - =(AVERAGE(J:M)+1)*50

FYI, this data is of very poor quality. Check the RAW EEG, you can see that AF7 has very bad skin contact throughout. You also have a bunch of warning markers all over the data for BF (Bad Fit). You should aim to have zero bad fit warning markers.

[tontine]

#1 - Yes
#2 - Bels
#3 - =(AVERAGE(J:M)+1)*50

Can you explain the function for averaging? Because the bel scale is logarithmic do we have to convert the bel values to linear, then average across all sensors, and convert back to bel? Thanks!

[James]

Average is Sum/Count.

[tontine]

Average is Sum/Count.

where does the +1 and *50 come from?

[James]

Values from the Interaxon SDK are in the approximate range -1:+1.
To convert these to the approximate range 0:100 to make them more understandable to the lay person you add one and times by 50.

[tontine]

Values from the Interaxon SDK are in the approximate range -1:+1.
To convert these to the approximate range 0:100 to make them more understandable to the lay person you add one and times by 50.

Cool, thanks. What about the issue of computing an average on a logarithmic scale?

[James]

You don't need to do anything extra. Average is still average.

[tontine]

You don't need to do anything extra. Average is still average.

The average of values in the bel scale require first converting to linear, then averaging, then converting back to bel. i.e. the average of 50dB and 100dB isn't 75dB. Or am I missing something?

[James]

The calculation uses logs but the results are linear. You don't need to do anything special to get an average