We used an event-related spatial working memory fMRI paradigm with 3 levels of working memory load. The task is a delayed-matching-to-sample task. First a sample with 1, 3 or 5 points (in 30 possible locations) is shown. Subsequently a probe with one point is shown. Participants have to press the left button if the probe point does not match the location of the previously shown 1, 3, or 5 points. If the probe matches the sample they have got to press the right button.
My question concerns the first level design-matrix:
The matrix consists of the following regressors:
2. Correct trials WM Load 1
3. Correct trials WM Load 2
4. Correct trials WM Load 3
1. Would it be valid to introduce two further regressors coding the correct and incorrect trials (for all WM loads together, some participants did not make any mistakes in the WM Load 1 conditions, else it would have been fine to introduce separate regressors for the three WM Load conditions)? My main concern introducing the correct and incorrect regressors is that the regressor coding the correct trials will not be independent from the regressors coding the correct trials for the single WM Load conditions.
2. What about missed trials? They will not be further analyzed in the imaging data analysis – so do I have to code them in a separate regressor? Or would it be ok to ignore the missed trials?
Thanks & Kind regards,