Triggers discriminating errors or correct responses

MicolG

Hello everyone,

By using Open Sesame, I am implementing my EEG experiment with participants seeing faces and trying to discrimante the emotional expressions displayed. Before and after my response prompt is displayed in the experiment, triggers with a predefined value (i.e., 27 or 28) have been set. I would really like that the triggers could disentangle whether participants give the correct response or not, by presenting a different value accordingly. In such a way, I can easily remove all the epochs in which the participants gave the wrong responses from my analyses.

In this regard, I would really appreciate your help.

Micol

Fab

Hi @MicolG,

I have no experience with the implementation of EEG triggers in OS but I assume you have that part under control and know how to send the trigger but just need help with defining its value depending on the subject's response accuracy.

There are two ways in which you can do this.

One is to use two versions of the trigger object (here I'm assuming you're using the parallel port -https://osdoc.cogsci.nl/3.3/manual/devices/parallel/- but the same principle would apply if you're using something else) and to condition their execution based on whether the subject's response is correct or not. You can access that from the correct variable (as long as you have defined included a correct_response column in your loop to tell OS what the correct response is in each trial (this can also be set through code if you prefer to do that dynamically). All you need then is to set your two trigger objects with the values you want to send to the EEG.

The [correct]==1 and [correct]!=1 conditions will be met when the response is correct and incorrect respectively.

The second method would be to use code to achieve the same result but with a single trigger object necessary. You could do that in Python or in Javascript. In Javascript (in the "Run" section, not the "Prepare section" of the inline script object), it would look like something like this (here I'm using trigger 29 for a correct response and 30 for an incorrect response):

if (vars.correct==1) {
   vars.mytrigger = 29;
} else {
   vars.mytrigger = 30;
}

Then you'd just need one trigger object but you'd set it up so that it takes its value from the mytrigger variable:

Hope this helps.

Fabrice.