Hi again… I’m trying to randomize both trials and events.

Let’s say I have the following events a1, a2, a3, b1, b2, b3, c1, c2 and c3. I would need randomize each class of stimuli (x1, x2 and x3), and additionally I would need to present each group (a, b, c) in a random order. For instance:

Run 1: a3, a1, a2, b1, b3, b2, c1, c2, c3

Run 2: b3, b2, b1, a2, a1, a3, c2, c1, c3

Run 3: a1, a3, a2, c2, c3, c2, b1, b2, b3

How do I program this? If I randomize trials at the block level, then groups (a, b and c) are not respected. If I randomize events at the trial level, events are not randomized at all!

Thanks!

Alvaro