Biosensor Array Galvanic Skin Response Spurious Input: Difference between revisions
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[[Category:Biosensor Array]] | |||
====== This page is part of the [[Biosensor Array]] Project ====== | |||
=== Advice on dealing with spurious input from [[Biosensor Array Galvanic Skin Response]] by [http://www.produceconsumerobot.com/truth/ Sean Montgomery] === | |||
<pre> | |||
---------- Forwarded message ---------- | |||
Date: Fri, 29 Apr 2011 14:42:57 -0400 | |||
From: Sean Montgomery <xxx@gmail.com> | |||
To: Drew Fustini <xxx@xxx.com> | |||
Subject: Re: GSR: eliminating spurious changes? | |||
Unless you're a hardware guru, software is usually easier to quickly try out | |||
a bunch of analyses and see what might work. You could use the Arduinoscope | |||
processing library (similar to one of the ones we published in Make | |||
Magazine) to plot the data along with some simple analyses and detections. | |||
-s | |||
On Fri, Apr 29, 2011 at 2:32 PM, Drew Fustini <xxx@xxx.com> wrote: | |||
Hi Sean, | |||
Thanks for your fast and detailed response. We've been learning a lot | |||
during the short build period and existing, well-documented projects like | |||
yours have been a big help. | |||
I like your suggestion of measuring numerous locations to reject spurious | |||
changes. I'm imaging that would be done best in software. Is that what you | |||
were thinking as well? | |||
Thanks! | |||
Drew | |||
---------- Forwarded message ---------- | |||
Date: Fri, 29 Apr 2011 14:09:40 -0400 | |||
From: Sean Montgomery <xxx@xxx.com> | |||
To: Drew Fustini <xxx@xxx.com> | |||
Subject: Re: GSR: eliminating spurious changes? | |||
Hi Drew, | |||
Ah, you've found the difficulties of bio-sensing... separating signal from | |||
noise. | |||
The problem you're experiencing is that when you move, you change the amount | |||
of contact between your finger and the electrode, thereby changing the | |||
resistance of the junction... exactly what the GSR is measuring. You can try | |||
to find a part of the body that is less likely to move during your | |||
behaviours of interest. I've gotten decent GSR from the wrist and not much | |||
success from the forehead, but fingers are the best I've found. You | |||
can measure GSR from numerous locations and reject spurious changes that | |||
only occur on one or two of the locations. You can also try to characterize | |||
the waveshape of real GSR responses and reject resistance changes that don't | |||
fit that criteria. | |||
Biosensing has huge potential, but is not without its hurdles. Some things | |||
are easier to measure like heart rate where you can more easily reject noise | |||
because of the stereotyped electrical signature. On the far end of the | |||
spectrum is EEG, where you're separating tiny electrical potentials in a sea | |||
of electrical noise and THEN trying to understand how those handful of | |||
electrical traces relate the hundreds of billions of neurons in the brain | |||
and the unknown (large) number of ongoing cognitive processes. | |||
Generally the trick is to understand your signal, what's creating it, what | |||
sorts of limitations that puts on your experimental paradigm. It's good to | |||
think about what kinds of workarounds are possible (as above), but also | |||
think about how you can limit the scope of your question to fit the | |||
attributes of the experimental tools that are available. | |||
Sorry no easy fix for ya. I'll be interested to know what you come up with. | |||
Cheers, | |||
Sean | |||
On Fri, Apr 29, 2011 at 1:34 PM, Drew Fustini <xxxx@xxxx.com> wrote: | |||
Hi Sean, | |||
I'm having a problem with finger cuffs which you note on the Truth | |||
Wristband page: | |||
"Note that physically moving the electrodes can create spurious changes in | |||
the resistance measured across the plates and contaminate our measurement. | |||
There are ways to work around this, but it's not completely trivial." | |||
I built the two-finger coper foil velcro cuffs and also the single-finger | |||
cuff from the wristband kit. The trouble I have from both is flexing or | |||
moving one's fingers generates a signal that I can't differentiate from | |||
actual GSR response (like poking my leg with scissors). | |||
Our biosensor array is design to be worn on one's body so having the hands | |||
motionless for accurate GSR isn't ideal. I'd really appreciate if you'd | |||
have any advise on how to eliminate spurious GSR readings due to movement. | |||
BTW, your Make co-author, Ira, pleasantly surprised me with a call to my | |||
desk phone to introduce an interesting biosensor data aggregation project | |||
he's getting organized :) | |||
Thanks! | |||
Drew | |||
</pre> | |||
