Auditory Steady-State Response with OpenBCI
Hi All,
Continuing with my work with OpenBCI, I'm trying to see if I can get an Auditory Steady State Response from my brain via OpenBCI. I'm seeing in the scientific literature that this is a technique that people are getting to work, so I figured that I'd give it a try. It was fun!
Here is a post describing my setup and my results (with my beloved spectrograms!):
After my success with SSVEP, I thought that I could nail ASSR on the first try. Sadly, I was not able to see any ASSR. I guess that it'll take more experimentation.
Any suggestions?
Chip
Comments
have you tried to get in touch with the Korean team?
E-mail address: [email protected]
I am pretty sure that they would help you.
They could send you some recording and you yours...
When you compute the average spectrum, try a wider window, 10 seconds, the peak, if it exists, will be sharper and higher, all the 40Hz energy being in a narrow band.
Yannick.
yj.
I went to the WAV Trigger site, cool little board, the writeup on the inventor is also amazing, he was a director of R&D for Walt Disney Imagineering,
http://robertsonics.com/about-2/
William
http://atlantsembedded.com/b/getting-started-auditory-steady-state-response-assr
[posted on their blog 21 February 2016]
William
- there're no details on what signal processing was done on the recordings and what the graphs show (They show amplitude vs frequency, but amplitude of what is that? What kind of averaging was done, if at all? Etc)
- the standard measure of response "strength" is magnitude-squared coherence (MSC) and its comparison to a critical value corresponding to a desired confidence level (e.g., 95%) - MSC_p. It is a standard result in statistics that an MSC of a single recording is 1, which is a meaningless result (coherence of a measurement of weight vs height from a single person is 1); therefore averaging over epochs in frequency domain is needed. It is surprising that with only 20 epochs (they call them "trials") they managed to get a decent SNR (which requires averaging in time domain, i.e. block averaging). It is also known that the more block averaging one does the higher MSC gets (since noise goes down), but the higher MSC_p becomes too (meaning that you need a higher result to convince it's not a fluke), so the reliability of the result is unclear.
- It is nice that they have relatively long epochs (I use 500 msec stimuli with 1 sec inter-stimuli windows) since this gives good true frequency resolution (1/T).
PS Good sources on MSC are:- "19890000-Analysis of Auditory Evoked Potentials by Magnitude-Squared Coherence", Dobie & Wilson
- "19930518-Objective response detection in the frequency domain", Dobie & Wilson
The formula for MSC_p is:- if the whole sweep is removed lots of good data is lost too and a lot of collecting effort is wasted
- it is incorrect to remove just a portion of a sweep since this affects the correctness of subsequent processing
This is one reason for processing of data in (relatively) short segments (usually, Hanning windows).(this is akin to why it's easy to make small LCD panels, but hard to make large ones)