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What matters with trial selection via the <block> element's /trials attribute is the *proportions you enter into the pool*. For example
/ trials = [16=noreplace(a,b)]
will sample randomly (without replacement) <trial a> and <trial b> in *equal proportions* / a 1:1 ratio. You'll end up with exactly 3 "a"trials and 3 "b"trials in random order. With
/ trials = [16=noreplace(a,a,b)]
the ratio is 2:1, i.e., you'll end up with 4 "a"trials and 2 "b"trials in random order. As to your own task, what you'll want to do is thus:
/ trials = [110=noreplace(stimulus1, stimulus1, stimulus1, stimulus1, stimulus1, stimulus1, stimulus1, stimulus2, stimulus3, stimulus4)]
