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| ====== This page is part of the [[Biosensor Array]] Project ====== | | ====== This page is part of the [[Biosensor Array]] Project ====== |
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− | == Advice on dealing with spurious input from [[Biosensor Array Galvanic Skin Response]] by [http://www.produceconsumerobot.com/truth/ Sean Montgomery] | + | == Advice on dealing with spurious input from [[Biosensor Array Galvanic Skin Response]] by [http://www.produceconsumerobot.com/truth/ Sean Montgomery] == |
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| + | ---------- Forwarded message ---------- |
| + | Date: Fri, 29 Apr 2011 14:42:57 -0400 |
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| + | |
| + | 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 |
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| + | |
| + | |
| + | |
| + | |
| + | 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 |
| + | |
| + | |
| + | 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 |
| + | |
| + | |
| + | |
| + | |
| + | |
| + | 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 |