Randomisation without consecutive presentations

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@Mirjam provides a general solution here:

In your specific case, something like this might work:

  • Insert a code component on your trial routine (from the “Custom” component panel).
  • In its “begin experiment” tab, put something like this ( we need to run this at the start of the experiment since the code is non-deterministic: we don’t know how long it will take to run (realistically though, it will be a fraction of a second for only 12 entries):
stimulus_list = ['v', 'b', 'n', 'm'] * 3
shuffle(stimulus_list)

# make sure the same target doesn't appear on consecutive trials
double_stim = False
list_ok = False

while list_ok == False:
    for i in range(len(stimulus_list) - 1):
        # check for equal neighbours:
        if stimulus_list[i] == stimulus_list[i + 1]:
            double_stim = True  # D'oh!
            break  # can stop checking on this run
    if double_stim == True:
        shuffle(stimulus_list)  # try a new order
        double_stim = False
    else:
        list_ok = True  # Yay! The loop won't run again.

print(stimulus_list)