Roy, i think everybody got it was a theory, and i suggest the guys were joking! But the thing is, we can check it! I may record the fragments on my PC in .wav format, then analyze the waves (as i did when i was a student), so it would be clear which pieces presented are the same and which are different, then, with all information, pass the test again and see the results. Could be the trick here, i mean the pairs presented in two different "drop-in"'s may not be the same; like, when you check it at 5 pm, you get pair #2 of the same tunes, and when you drop in again like at 5:30 pm the pair #2 consists of two slightly different tunes... i, for instance, cannot memorize 30 pairs of tunes note by note! I had three different results at three drop-ins: 26, 24 and then "reversed" 25 (5/30).
The question is, is this investigation really needed... and when will i have enough spare time to try it...

eh, did i ever say i was all optimist?..