Hi Bobby!!
You had absolutely the right intuition!!! 
This way it works well!!! Indeed the loop must be incremented beforehand by 1!
Ok, I have the last strange issue that I could not easily solve.
My experiment runs well, however, I have a little nuisance with the data output.
Obviously it collects the response anytime it enters in the inner loop, and attach it to the output. (at the moment the inner loop the box “Is trial” is checked (as it should be I suppose?).
However the data output also shows an additional row which refer to the condition that has been picked from the block list referred from the outer loop. Is there a way to have this on the same Row ?
Below an example of how the data look like!
As you can see the first row refers to the response collected while the second row refers to the “blockloop” and indicates the corresponding condition.
I have seen there is another post about this:
But none of the solutions proposed there seemed to work for my case?
Thanks again for your help