recording only external (eye) electrodes

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clavicord
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Joined: Thu Mar 12, 2009 11:18 am
Location: Leipzig

recording only external (eye) electrodes

Post by clavicord »

hi all,

for a behavioral study we need to control eye movements in a convenient way. We tried to record external eye - but not scalp - electrodes with our Active Two system. However, there is an error message reporting a ringbuffer overflow. This might be related to the missing DRL and an inadequate config-file, for we use the one for included scalp electrodes.

What is the best (=easiest ;) ) solution for the problem?

best regards,
tobias

Coen
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Post by Coen »

A ringbuffer overflow means that the PC is not able to keep up with the incoming data stream. Basically, the problem can only be solved with a faster processor in your acquisition PC

A CMS and DRL electrodes is always necessary, also if you only use the flat electrodes (EX inputs).

The ringbuffer overflow problem is not directly connected with CMS/DRL or CFG isues. However, CMS/DRL problems, or loose hanging channels can cause rail-to-rail noise traces, which need more processor power to display. This may eventually cause a buffer overflow in cases were there is not much headroom in terms of processor power to begin with.

Reducing the sample rate, switching off filters, and only displaying a limited number of channels decreases the processor load during acquisition.

Best regards, Coen (BioSemi)

clavicord
Posts: 2
Joined: Thu Mar 12, 2009 11:18 am
Location: Leipzig

Post by clavicord »

that's interesting! I think we didn't encounter performance problems recently. But until now, we didn't try to record externals only.
about the recording of eye channels: What a pity that there is no easy solution for that. however, thx coen for the nice reply!

best regards,
tobias

Coen
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Joined: Fri Mar 26, 2004 7:00 pm
Location: Amsterdam, Netherlands
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Post by Coen »

If you could record previously with many headcap channels, then there should be no problem at all with recording just the 8 EXG electrodes. You will just need the separate CMS/DRL lead (connection to the front panel of the AD-box).

Best regards, Coen (BioSemi)

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