Onset timing files with fMRI data

Hi everyone,

I have a question regarding the format of onset timing files in FSL. I know that the general format is onset, duration and stimulus type/correct or incorrect response. However, for the stimulus type I have different conditions such as right execute, bi-imagine, right imagine and so forth?

Please see a screenshot below:

image

When I select this file in FSL to run the first-level analysis, I get an error saying that there is a problem with the onset timing file.

Does anyone know how I can work around this problem or can anyone suggest what I need to do here?

Thank you so much for your help.

Best regards,

Rubina Chandnani

Hi Rubina,

You’re nearly there. The files you need do have a three-column format. Column 1 should be the onset time (in seconds), column 2 should be the duration of each event, and column 3 should be a parametric weighting factor (mostly this will be 1, unless you’ve got a parametric design - probably you haven’t). You’ll need separate files like this for each of the conditions or event types you want to model in your design matrix. So one will look like this:
62.3 1 1
63.3 1 1
etc.
…for all your right execute events, then you’ll need a separate one for each of your other event types, as each event type will need its own regressor in your design matrix.

(By the way, are your trials really only one second apart? That’s a pretty unconventional design for fMRI, and you’ll struggle to be able to resolve individual trials on that time-scale. If you have four trials that are the same that close together, you’re probably better off modelling them as a single block.)

Hope that helps!
Matt.

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Hi Matt,

Thank you so much for your response.

I did figure it out eventually. Yes, that’s exactly the plan, I’m going to model the EVs for each condition as a single block.

Many thanks once again.

Best,

Rubina

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