Unwanted triggers during ABR measurement

[NVanderStoep]

Dear sir, madam,

recently we have acquired the ABR cord and input and have been able to record decent ABRs using a stimulus with fixed intensity and a single triggercode (sent synchronously with the click onset). We are now also able to present clicks with different amplitudes and different triggercodes. However, somehow we get additional triggers when checking marker quantities using Brain Vision Analyzer (BVA). The additional trigger codes (3 in screenshot) can often be found at the same time as a marker we actually want (10 or 11) or at the down slope a coupe of samples later (see attached picture). We always send a 0 after a stimulus trigger (e.g. 10, integer) and have a couple of milliseconds in between the 0 trigger and the next stimulus trigger. Using our setup (see below), trigger lines 9-16 are always high (rainbow colors in ActiABR) and stimulus triggers show up in triggerlines 1-8 (should all 16 trigger lines be 0 for triggers to work properly?).

I am not sure what we are doing wrong and how to solve the extra triggers. The extra triggers are problematic because they can overlap with other trigger codes we use. I hope you can help us out.

Kind regards,
Nathan

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Screenshot
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Ghost trigger.png (243.34 KiB) Viewed 39796 times

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Some more information on our setup:
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Setup:
PC running Windows, Eprime 3.
PST Chronos box with IO expander for synchronization of sound onsets and trigger onset (works via USB, https://pstnet.com/products/chronos/).
BioSemi AD box and battery box with ABR Cord and ABR input (speedmode 9).
ActiABR for recording.
Brain Vision Analyzer for offline dataprocessing.
TDH-39 headphones connected to PST Chronos audio out.

Stimuli:
100 microsecond clicks (square wave) followed by 10 ms silence.
Interstimulus interval 27 ms, 37 Hz presentation rate.

[Coen]

The problem may be that your trigger generator does not switch the separate lines (bits) within one sample period (62 microsecond). Try using trigger values that switch only one line, e.i. 1,2,4,8,16,32,64 and 128.

High (unconnected) lines 9-16 do not cause false triggers.

Best regards, Coen (BioSemi)

[NVanderStoep]

Thanks for the quick reply and suggestion. I will check whether this resolves the issue coming week and report back.

Kind regards,
Nathan

[NVanderStoep]

Hi Coen,

your suggestion resulted in zero unwanted triggers with 24000 samples. That is great. However, we need more than 8 trigger codes. Do you have any idea how we could make this happen?

Best,
Nathan

[Coen]

Use all 16 trigger lines or use D flip-flops to latch the triggers and sent them to the USB-receiver on the same moment (also see viewtopic.php?f=1&t=53&p=144 , sample clock is available on pin 32 of the trigger port)

Best regards, Coen (BioSemi)

[Kenyon]

Hello,

Similar to the issue raised by the OP ActiView is showing triggers coming in on lines 9-16 at what appears to be a constant rate of 16 Hz. The trigger “1” (256) is sent over and over again. No changes have been made to the hardware. I recently upgraded the software to the 64 bit version for macOS, but have successfully acquired data several times since then. This seemingly has started “spontaneously”. This is extremely disruptive because the trigger that I am sending on lines 1-8 are being affected when they happen to co-occur with lines 9-16, effectively changing the stimulus locked event code. Based on the fix suggested in this thread, I’ve modified the cfg file to set RespSwitch=0. This seems to have fixed the problem. However, I’m concerned/curious as to why this would’ve started happening “spontaneously” in the first place. I’d appreciate any thoughts you might haver on the matter.

[Coen]

ERGO's have floating CMOS (high impedance) inputs. When nothing is connected, the smallest charge pickup can cause random drift and switching, see traces in the "Auxiliary Sensors" tabpage. You describe normal behavior.

With the "0" setting in the CFG, the ERGO's are disconnect from the trigger lines. Don't forget to reset the CFG when you want to use response buttons connected to the ERGO

Best regards, Coen (BioSemi)

[NVanderStoep]

The problem may be that your trigger generator does not switch the separate lines (bits) within one sample period (62 microsecond). Try using trigger values that switch only one line, e.i. 1,2,4,8,16,32,64 and 128.

High (unconnected) lines 9-16 do not cause false triggers.

Best regards, Coen (BioSemi)

Thanks Coen, we’ve got it working with your solution. Thanks for the help!