Equal frequency of sequences of block items

Mkengine

Hi, I hope this is the right forum.

I am new to Opensesame (and Python in general), so maybe there already exists a solution for my problem: I have one column for the direction of a triangle (up and down) and I need to get a sequence where, on the one hand the list is randomized, but on the other hand repetition and switching of these items should occur with equal frequency, such that up -> up; down -> down; up -> down and down -> up occur equally often. Would this be implementable?

Thanks in advance

Tobi

eduard

Hi Tobi,

Yes, that is possible, but requires direct Python coding and is quite tricky to efficiently and robustly script. Something like this could work:

import random
n_trials = 21
n_transitions = 20
n_stim = 2
n_transtypes = 4


while True:
  stim1_trans = ['rep','swi']*(n_transitions/4)
  stim2_trans = ['rep','swi']*(n_transitions/4)
  random.shuffle(stim1_trans)
  random.shuffle(stim2_trans)
  trans_list = [stim1_trans,stim2_trans]
  try:
    seq = [random.choice([0,1])]
    for i in range(n_transitions):
        prev = seq[-1]
        cur = trans_list[prev].pop()
        if cur == 'rep':
            seq.append(prev)
        else:
            seq.append(prev^1)
  except:
      continue
  else:
     break

Only problem is that the code is not robust enough to produce a sequence that has the certain length without crashing. Therefore, I wrapped it into a while loop to keep on running until it happened to work. That is of course a weird and slightly ugly solution, but does produce valid sequences (I think).

Good luck,

Eduard