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Join Date: Feb 2017
Rebecca_Hirst is on a distinguished road Posts: 1
Hi there,

I am checking the latency between when I call an auditory stimulus to play and when it actually occurs - using the auditory inputs on the Cerdrus stick tracker.

I labelled my event trigger as '151' and see this trigger appear in the trigger line along the bottom of actiview when recording. I also see an event '12' appear in actiview which I assume is the stim trackers marker for actually playing the sound.

However when I try and view the events in EEGLab sometimes '151' appears sporadically and sometimes not at all. I also never see the trigger 12 and instead see either 2199 or 2048 (interestingly the difference between the two is always 151- not sure if this is relevant ?).

I was wondering how to know if the trigger i sent was actually received and recorded ? How do I ensure the triggers I send can be viewed ? And how do I know when trigger represents the stim trackers marker for auditiory input?

On a side note I also think the occurrence of the trigger seems to depend on the settings through which I present my sound. I present my sounds using psychopy which has two settings 'pygame' and 'pyo'. The latter is known to suffer less latency issues. However the trigger is always visible when using pygame and not always visible when using pyo.

Thanks in advance,

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Join Date: Aug 2006
Location: San Pedro, CA
Hisham is on a distinguished road Posts: 1,124
Posted 3 Weeks Ago #2
The best way to understand what’s going on is to send to StimTracker only one input source at a time. Even for audio, you need to send a sound on only one channel at a time -- either left or right, but not both at the same time. This will make it clear what the signals correspond to.

I am not familiar with the specifics of ActiView. But it is common for EEG software to display the decimal value of the combined input lines. When only one line is selected at a time, you will see values like 1, 2, 4, 8, 16, 32, 64, 128, etc. When more than one line is selected, you will see a combined value.

I hope this answers the right question!
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eeglab, psychopy, pygame, pyo, trigger
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