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penades
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Hi,

we are using a Cedrus RB-530 response pad while recording EEG with an EGI sensor net in a reaction time task.

We have noticed that every time the subject presses a button of the pad an artifact (around 6 mV) appears in the EEG signal. We know that it is not elicited by finger movement.

Anybody has noticed anything similar in the EEG recording?

What can we do to avoid these kind of artifacts?

Thanks a lot!
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Hisham
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Posted May 21st, 2010 #2
Is the RB-530 connected to EGI via the Accessory Connector?
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penades
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Hi Hisham,

no, we use a USB connection between the response pad and a computer with Presentation software, that is connected to EGI computer via parallel port.

After some test, we have noticed that the artifact occurs only when the person who wears the net presses the button (but not if another person without the net presses it). It seems that some voltage is transmitted from the pad troughout the subjet's finger and we can see that voltage in several sensors of the net, specially in those around the sensor that is used as ground.

Maybe we have a problem with grounds, we have to investigate it deeply and ask EGI support but, could a voltage be trasmitted from the pad to the subject?

Thanks a lot for your attention
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Hisham
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Posted May 24th, 2010 #4
We've had another user run into this. That user was getting 3mV artifacts when the participant simply moved their hand on the response pad.

The solution is to isolate the response pad's ground from the computer ground -- easier said that done. In the case of the other user, he supplied the response pad with battery power through the USB connector and collected the data on button presses via the Accessory Connector.
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penades
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Thanks a lot Hisham,

I'll try the first option (isolate response pad's ground from computer ground), but I really donīt know how to do it. I need some clue... Is some physically action in the computer hardware needed? or can I get it via any configuration panel of windows?

About the accessory connector, do you known the time accuracy of this kind of connection? USB connection is about 5 ms...what about the accessory connector?

Thank you for the help!
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Hisham
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Posted May 25th, 2010 #6
Battery power is the easiest power source to find and use that has an isolated ground. To use it:
  1. Get a USB cable that you won't miss.

  2. Buy a battery holder that can hold three 1.5 volt batteries, for a total of 4.5 volts. These can be purchased at Digikey or Mouser. Radio Shack might have some. If it's too much trouble and you're handy, you can buy a flashlight that takes three batteries, dump the light bulb, and use the flashlight as a glorified battery holder. You get a free on/off switch with it.

  3. On the USB cable, cut the connector that goes into the computer.

  4. The USB cable has four conductors, or wires: two for data send/receive, one for ground, and one for positive voltage. Ignore the data wires and connect the other two to the battery holder.
At this point, if you've done everything correctly, the other end of the USB cable is ready to plug into the response pad to power it up.

Regarding timing, the Accessory Connector will put out the signal within 1 millisecond. So does the USB connector, but we're not using the USB data here. Remember, the 5ms figure that you mention is due to the USB driver that's running on the computer.
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penades
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Batteries, Posted May 31st, 2010 #7
Hi Hisham,

first of all, I've tried to use a battery of 9 v as of the response pad's power source and it does't work. Is it too much voltage? You told me that I had to use tree batteries of 1.5 v (4.5 v)... maybe using 9 v could be a problem.

Moreover, I've noticed that the response pad needs the drivers to be powered (if I connect the response pad in a computer without RB drivers installed it is not powered)...I canīt install drivers in a flashlight

We had powered the response pad with a secondary PC working with battery (not plugged to the general net) and the artifact remains. We cut the ethernet cable and used their pins as serial inputs because we can't communicate via Accessory connector.

Finally, I'm working with Presentation software and it actually allows TCP/IP connections but it demands a hostname to work. It seems that this utility has been designed to connect two computers. Has the response pad any TCP/IP direction, any hostname? in order to get a comunication Presentation-response pad??

Thanks a lot!!
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Hisham
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Posted July 11th, 2010 #8
If you still haven't resolved this, please call me at the office on or after July 15 (I'm out of the office until then). Some issues are faster resolved over the phone. 1.800.CEDRUS1 (that's 1.800.233.7871).
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SylviaG
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Hello, I was conducting an internet search of a button press artifact when I came across this thread. My lab is currently using an EGI system to collect EEG data and several of the tasks that we have designed requires a response. We have been using the Cedrus response box (RB-540) and have noticed an artifact like the one described in this post. We have also tried an external keypad and noticed it as well. I was interested if there was a solution to this problem. Attached is an image of the artifact where the where in the green and blue line condition the participant is pressing a button that results in a tone (occurring at 0ms). Thank you in advance for your time.
Attached Images
File Type: png buttonartifact.png (12.6 KB, 1 views)
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Hisham
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Posted June 7th, 2018 #10
It’s hard to troubleshoot at a distance, so perhaps some questions first. :-)

1. How is your RB-540 connected to EGI? are you using m-pod?

2. Does your USB cable have ferrite cores on it? These look like the round white blocks in the picture below that are clamped near the connectors on each end.

3. If I may ask, where are you geographically located?


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