Randomizing both trials and events

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!



You’re using stimulus lists, right?

If you have a stimulus list with twenty items, and it’s attached to an event as the only event in a trial, then this will wind up spawning twenty trials each with only one event, so randomizing events within the trial will have no effect.

Given your [a-c][1-3] scenario, the simplest way to set this up would be with three trials, each with three events, and NO stimulus lists.

Unfortunately, that limits what we can do before or after your stimuli. If you need something more complicated, we may be able to get it to work with macros, but I’ll need to know more about how your experiment is really laid out.

Thanks, Hank!

Things got quite busy in the lab and I’ll start working again on this experiment in the next few days.