setting up GSR

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EJB
Posts: 5
Joined: Wed Feb 10, 2016 5:23 pm

setting up GSR

Post by EJB » Wed Feb 10, 2016 5:47 pm

Hello,

I'm new to Biosemi and I'm trying to figure out how to record just GSR for my experiment. I have a few questions:

1. Where should I place the CMS/DRL electrodes? On the ActiveTwo GSR manual it sais to place them on the back of the hand (see http://www.hum.uu.nl/uilots/lab/resources/GSR.PDF). However, this website (http://uilots-labs.wp.hum.uu.nl/how-to/ ... equipment/) sais it's better to attach them to the forehead. In either case, how do I actually attach the electrodes? The ones I have are made to be attached through the headcap. Does this mean that if I place them on the forehead I have to also apply the headcap (even though I'm not recording EEG)? If I place them on the back of the hand (I assume the same hand as where I'm attaching the GSR electrodes), how do you suggest I attach them? (what I've done is placing a bit of gel in two locations on the back of the hand, placing the electrodes on top and taping them down; this seems a pretty unorthodox method so if there's any better way let me know).

2. From reading the GSR manual cited above, it's unclear to me what the sampling rate is and if I can change it in any way through ActiView. I have previously used sampling rates of 500 Hz through Biopac. From the GSR manual it looks like the sampling rate is 32Hz, which seems very low for the kind of precision I'm looking for. Have I misread the manual?

3. On this manual (http://socrates.berkeley.edu/~lynnlab/i ... ection.pdf) is indicated that before starting to record, I should open a configuration file. This website (http://uilots-labs.wp.hum.uu.nl/how-to/ ... equipment/) sais that the configuration file should be in C:\Program Files\Biosemi\ActiView706_Lores\Only_GSR.cfg. However I don't have any such file. Is there somewhere I can download it from? Is it necessary for me to open it before recording GSR?

4. This is also not about hardware but I thought I should have all my questions in one post. Once I recorded some GSR data, I saved it as a bdf file. Now I'm trying to open the file on Matlab using the script I downloaded from here http://www.biosemi.com/download.htm. However I can't get the function ImportEDFHeader to open my file; the error message is "Undefined variable "GSR_Trial2"", where that's the name of my file, even though both the files and the functions are in the same directory which is set as a path. Do you have any suggestions or is there any manual for how to use those scripts?


Thank you very much!

Coen
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Re: setting up GSR

Post by Coen » Thu Feb 11, 2016 12:35 pm

GSR is used with flat (not pin) passive electrodes, attach them with advise disks.

GSR signal is initially sampled at 32 Hz (analog bandwidth is 16 Hz) and then up-sampled to the selected sample rate of the EEG channels.

No special CFG is needed for GSR.

Best regards, Coen (BioSemi)

EJB
Posts: 5
Joined: Wed Feb 10, 2016 5:23 pm

Re: setting up GSR

Post by EJB » Thu Feb 11, 2016 7:08 pm

Dear Coen,

Thanks so much for your reply!

I have the passive flat GSR electrodes but what I'm asking about are the CMS/DRL electrodes, which the GSR manual indicates should be placed on the back of the hand. Are there flat versions of those electrodes?

Since I'm not using EEG in my experiment (just GSR), how can I change the sampling rate then?

Thanks!

Coen
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Posts: 899
Joined: Fri Mar 26, 2004 7:00 pm
Location: Amsterdam, Netherlands
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Re: setting up GSR

Post by Coen » Fri Feb 12, 2016 1:11 pm

A CMS/DRL set with flat electrodes is available at EUR 100, connection to the front-panel of the AD-box.

Change the sample rate with speedmode rotary switch on the AD-box (http://www.biosemi.com/faq/adjust_samplerate.htm) and the DECIMATON selector (left side bar in ActiView). This changes the sample rate on file but the GSR bandwidth always remains 16 Hz (for EEG channels, the bandwidth is 1/5th of the selcted sample rate).

Best regards, Coen (BioSemi)

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