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Actually, I understand the question a bit differently. From what I gather, the goal is to ensure that each possible primetarget combination is realized (a combinatorial problem). So, prime #1 needs to precede each of the 8 positive targets and each of the 8 negative targets *exactly* once. Same goes for prime #2 and so on to prime # 16. This will yield 128 positive trials (16 primes * 8 positive targets) and 128 negative trials (16 primes * 8 negative targets). I think, the right way to pull this off is to use a set of 2(positive, negative) * 2(prime, target) counters for the item selection that contain the "hardcoded" permutations. For example, <counter counter_primes_positive> would list the item numbers for your 16 primes (8 times each because each prime needs to be combined with each positive target).
<counter counter_primes_positive> / select = noreplace / items = ( 1,1,1,1,1,1,1,1, 2,2,2,2,2,2,2,2, 3,3,3,3,3,3,3,3, 4,4,4,4,4,4,4,4, 5,5,5,5,5,5,5,5, 6,6,6,6,6,6,6,6, 7,7,7,7,7,7,7,7, 8,8,8,8,8,8,8,8, 9,9,9,9,9,9,9,9, 10,10,10,10,10,10,10,10, 11,11,11,11,11,11,11,11, 12,12,12,12,12,12,12,12, 13,13,13,13,13,13,13,13, 14,14,14,14,14,14,14,14, 15,15,15,15,15,15,15,15, 16,16,16,16,16,16,16,16) </counter>
The corresponding target counter would list the item numbers for the positive targets like this:
<counter counter_targets_positive> / select = current(counter_primes_positive) / items = ( 1,2,3,4,5,6,7,8, 1,2,3,4,5,6,7,8, 1,2,3,4,5,6,7,8, 1,2,3,4,5,6,7,8, 1,2,3,4,5,6,7,8, 1,2,3,4,5,6,7,8, 1,2,3,4,5,6,7,8, 1,2,3,4,5,6,7,8, 1,2,3,4,5,6,7,8, 1,2,3,4,5,6,7,8, 1,2,3,4,5,6,7,8, 1,2,3,4,5,6,7,8, 1,2,3,4,5,6,7,8, 1,2,3,4,5,6,7,8, 1,2,3,4,5,6,7,8, 1,2,3,4,5,6,7,8) </counter>
With these two counters, each possible primetarget combination will be shown in your 128 positive trials. The same thing, of course, also needs to be done for the 128 negative trials. I've attached a small template script containing all necessary elements for further reference. My testing data show that the script performs as desired (each primetarget combination is run once in random order). Actually, this was fun!
Best, ~Dave
