Accelerometer / data / rational

Comments

• chipaudette

  November 2014

  From my perspective the accelerometer is useful as auxiliary data to help reconstruct what happened during and EEG recording session.  For example, if the OpenBCI board is strapped to the head, it can help figure out the head's orientation (thought a 3-axis magnetometer might have been better for this purpose).  Or, if one detects a lot of bouncing or jiggling via the accelerometer data, then you can better understand why there might be so much motion artifact in the EEG recording.

  
  

  Another use for the accelerometer is as a user input method.  For example, if you're wearing your EEG electrodes during an experiment (say, a meditation experiment) you might want to put some sort of marker into the data to say "now is when I started the next phase of my experiment".  Without the accelerometer, you'd want to wire up a button to the OpenBCI board, or you'd need to push a button on the datalogging software on the PC.  With the accelerometer, however, you can simply tap your fingers on the OpenBCI board a couple of times.  You'll easily see this tapping in the accelerometer data and so you'll know when you started that phase of the experiment.  Quite useful!

  
  

  Chip
• chipaudette

  November 2014

  Continuing the discussion of the usefulness of the accelerometer, I was doing other research and came across this paper from the US Army Research Laboratory:

  
  

  http://www.dtic.mil/get-tr-doc/pdf?AD=ADA506020  (you might need to try it twice, it often gives an error the first time)
  

  
  

  This study looks at the feasibility of getting EEG recordings from subjects who are not just sitting still.  They're looking at the effect of the bodily motion on the quality of the EEG signals.  In particular, they look a lot at the corruption in the EEG signals due to the motion.  Physical motion causes a lot of EEG corruption, so this is an important thing to study if you ever want to measure EEG from real people out in the real world (and not just in the lab).

  
  

  One of their findings is that the frequency content of the physical motion often translates directly into the frequency content of the corruption in the EEG signals.  Therefore, if you know the physical motion, you can do a better job dealing with the motion artifact...perhaps in a very quantitative way.  

  
  

  While this might seem like an obvious recommendation, it is important to note that it is very uncommon for traditional EEG systems to include any sensors to measure motion.  As a result, you'd have little data to know whether an interesting EEG feature was real (ie, from the brain) or was an artifact of some sort of physical motion.

  
  

  Since OpenBCI includes a 3-axis accelerometer, this additional data about a person's motion might prove useful to resolve these kinds of ambiguities.  Since I'd expect that all of the most interesting uses of OpenBCI will be with folks using it out in the real world (ie, not buried in some research lab), this information about one's physical motion could be really helpful.

  
  

  Chip
• chipaudette

  December 2014

  I collected some data from the accelerometer for the first time.  If you're interested, you can see some data at:

  
  

  http://eeghacker.blogspot.com/2014/12/openbci-accelerometer-data.html
  

  
  

  Looks pretty good!

  
  

  Chip