I have addressed a similar issue in creating my design scripts. What I do is up front create all possible regressors, eg: Correct Cond A / Incorrect Condition A / Correct Condition B / Incorrect Condition B ...

Then I cycle through my behavioral results file (trial specific responses collected at the time of the scanning) and fill in the different regressors. Then I go back and check to see if any regressors are empty. If so, the program removes them and all that is left are the non-empty regressors which go into my model. 

The next thing to consider is how do you compare correct vs incorrect if the proportions are strongly in favor of correct. So if you have 25 correct trials and 5 incorrect trials.

For that I do not have a good answer and am looking forward to what others have to say.

 I hope this helps,

Jason

On Mon, Dec 8, 2008 at 10:46 AM, Marko Wilke <[log in to unmask]> wrote:

Hi,

there was a response to a similar question a while ago suggesting that you include a "dummy mistake" at the very last scan. The effect of this will only be taken into account (due to the shift of the HRF) when you are already done scanning, so it will not really make a difference (but it may allow you to specify your model). Perhaps this is worth a try.

Best,
Marko

Tully, Joseph (NIH/NIMH) [V] schrieb:

Hi everyone,

 
My problem is that I'm trying to differentiate between correct & incorrect responses on an fMRI task over the course of 4 runs. The problem is that some people did really well or really poorly in certain runs. For example, subject A may have gotten 100% correct/0% incorrect on the task during run 1. As far as I can tell, this means that it is impossible to Specify 1^st Level and run the program, since the program assumes I've made a mistake and left something in blank rather than the subject literally having 0% incorrect. Is there a way to collapse all 4 runs together so I can still make this comparison between correct & incorrect responses?

 
Thanks,

Joe

 
 

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Marko Wilke                                            (Dr.med./M.D.)
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Universitäts-Kinderklinik              University Children's Hospital
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