Serial USB relay: Adding time-stamps to EEG Recordings

[Jodie]

Hello Forum,

I am having a little bit of trouble with my USB relay setup. Essentially, I have a USB 4-relay board which I using to communicate between E-prime and Biosemi.

My plan is to timestamp in the EEG recording when the stimulus event is being shown. My current script is the following (which just opens and closes the USB relay):

This in-line is immediately before the stimulus presentation:

----------------------------------

Dim arrDataa(2) As Integer

arrDatag(0) = 255

arrDatag(1) = 1

arrDatag(2) = 1 

Serial.WriteBytes arrDataa

---------------------------------

Following by the Stimulus presentation

Then, this in-line is immediately after the stimulus presentation:

----------------------------------

Dim arrDatab(2) As Integer

arrDatag(0) = 255

arrDatag(1) = 1

arrDatag(2) = 0 

Serial.WriteBytes arrDatab

---------------------------------

The script works nicely and is able to time-stamp into the Biosemi recording. The problem is that while it works perfectly for when the trigger code is sent (lets say a 64 time-stamp appears in the trigger of Biosemi), when I 'stop' the trigger (after the stimulus is presented), there is a time-stamp of 64 with a zero underneath in the Biosemi recordings. This is problematic for when I try to analyse the EEG data because all of the start and stop events are saved as the same 64 time-stamps (it ignores the zero below the 64 in the 'stop' time-stamp condition) and therefore, the 'stop' is considered the same event as the initiation of the time-stamp. 

I contacted Biosemi and they told me that the issue is with the scripting in E-prime. I was wondering if anyone had any suggestions for how to fix this problem? 

It would be much appreciated!!

I hope I have been clear?

Thank you for your help.

Kind regards,

Jodie

[Paul Groot]

Hi Jodie,

I don't see why this should be an eprime issue? The logic behind your script is that there is an active digital signal when the stimulus is presented. Not sure how biosemi normally encodes those events, but if it encodes rising and falling edges seperatly, there is no way of preventing the additional marker at the end of the stimulus. However, I doubt if the digital interface with relays is the right way to conenct the two systems. Relays can cause delay and bouncing problems, so I would prefer a direct (TTL) connection from the stimulus computer to the biosemi trigger input(s). Normally this can be done using a parallel printer port or IO board. I would be very suspicious about a possible bouncing issue when the relay is switched off. Especially when using high sampling rates...

Best

Paul

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[Jodie Feil]

Dear Paul,

Thank you for your advice. 

You were right, there was 'bouncing' at the end of the falling edge, which was in part, causing the problem and additional unwanted events. 

I am only interested with the 'rising' and not the falling edges (which in my case does not have delay/bouncing issue), so I have found a way to work around the problem of the bouncing in the falling by re-programming some functions in EEGLAB (which remove the falling bounce).

I will also try using a parallel port and see if it is a better option.  

Regards,

Jodie 

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Dr.Jodie Naim-Feil

Post-doctoral Fellow

Research group of Elisha Moses

Department of Physics of Complex Systems

Weizmann Institute of Science

76100 Rehovot, Israel