Getting 'usable' readings in Muse Lab // Processing via muse-io


#1

Dear forum,

yesterday I received my Muse headband. I am trying to get it up and running with Processing (processing.org).
I can couple the device via muse-io and stream to OSC. In Muse Lab, all channels seem to broadcast, but regarding the incoming data, the only useful (out of the box) seems to be from the accelerometers.

The connection overview icon shows good connection on all sensors.
The eeg channels have readings around 800 to 850 unicorn units (Seriously, what is this? uV? I read about an offset of 800 unicorn units somewhere here in the forum). Everything, that is being processed from there (elements/alpha, beta, …) has an output of zero point something, but reference channels show huge spikes. Quantized EEG data is always 1.

How am I supposed to treat these values to handle them properly? Are the processed values in an inverse logarithmic scale? I can just make wild guesses right now, because I am totally missing a proper documentation. If there is one, where can I find it?

Some small compendium / documentation for the used sensors, to-be-expected reading levels and what not would be very, very helpful to get into this device.

Also: Can someone provide me with a proper recording of .muse data, so I can verify my sensor readings against that?

That would be super-awesome :slight_smile:

Best regards from Aachen, Germany
Frederik


#2

So after revisiting some of my searches from the past week, I found this: https://sites.google.com/a/interaxon.ca/muse-developer-site/museio/osc-paths/osc-paths---v3-6-0

Sorry, I missed that :confused:


#3

Hi Frederik,

Glad you managed to find the documentation for the data available from MuseIO!

The EEG units are indeed in microvolts. I’ve discussed the ~800uV offset in a few different threads here, to quote from a particular one:

There will always be a DC offset in the EEG data. The offset is in REF as well as the data, because due to the amplifier configuration in Muse the DC difference is not amplified, just the AC difference is. The offset appears un-amplified at the input to our ADC, and is approximately at the ADC’s midpoint. If you use the conversion factor that we mention in our documentation to convert amplified ADC values to uV, this comes out to around 800uV. However, the conversion factor is calculated to account for AC signals that have been amplified, and remember, the DC offset does not get amplified.

So the 800uV mean is not [I]really[/I] 800uV. But it’s not [I]really[/I] the mean that you’re interested in. The long-term mean of the signal is probably useful for only a few things like the skin-electrode half cell potential. Really what you’re interested in is the peak-to-peak amplitude of signals, whether they be slow or fast-changing. Even if you want to investigate the behaviour of a signal which changes very slowly, the useful information is contained in how it changes, not in what mean it is centred around.

​Hope that helps!


#4

Thanks Tom,

I read that post of yours sometime this week (while waiting for my device :p).
I am not a neuro scientist, but a product designer and I am just starting to dig my way into the somewhat abstract matter of “trying to look into the brain”.


#5

There will always be a DC offset in the EEG data. The offset is in REF as well as the data, because due to the amplifier configuration in Muse the DC difference is not amplified, just the AC difference is. The offset appears un-amplified at the input to our ADC, and is approximately at the ADC’s midpoint. If you use the conversion factor that we mention in our documentation to convert amplified ADC values to uV, this comes out to around 800uV. However, the conversion factor is calculated to account for AC signals that have been amplified, and remember, the DC offset does not get amplified.So the 800uV mean is not [I]really[/I] 800uV.

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