A) would generally work fine.

The only reason you might not want to use (A) is if you don't have   
many blocks per condition
in this case, you can use :
C) Have two EVs - one defines the block timings, and the other is the  
weighting EV

If you just have the weighting EV, you cannot tell whether an effect  
is really correlated with weighting, or if it is just condition A  
itself that causes the effect


On 8 Jan 2008, at 15:31, Hanne Lehn wrote:

> Hi,
> I have data from a block design experiment with two conditions, A  
> and B.
> I'm interested in whether activation in condition A is modulated by  
> task
> performance. Performance was measured throughout the experiment and  
> has a
> separate value (0-6) assigned to each block. How do I set up the
> appropriate first-level analysis? Do I
> (A) create 7 EVs for condition A, one for each level of  
> performance, and
> compare their effects with the appropriate contrasts?
> or
> (B) create 1 EV for condition A which includes all blocks, then add  
> the
> performance variable as a weighting factor (use performance scores  
> instead
> of "1"s in the third column of my custom onset file)?
> Hope my question is clear.
> Many thanks in advance!
> Hanne