I am unable to randomize blocks in my Psychopy study? What can I do?

Question

:slight_smile:

What are you trying to achieve?:

I am currently doing a reaction time and accuracy task that involves comparing visually presented numerical information and auditory numerical information. The visually presented numerical information will be presented in three forms - Arabic numerals (e.g 5), number words (e.g five), and non-symbolic magnitude (a picture of 5 dots). Both visual numerical information and auditory numerical information will be presented sequentially. After the presentation of the 2nd stimulus, participants are to respond if these two stimuli are conveying the same information or not. They are supposed to press “a” if the numerical information is the same and “l” if it’s different.

Apart from varying the format of the visual numerical stimuli I am presenting, I also intend to vary the stimulus onset asynchrony (SOA)/time interval between the two stimuli. I have 7 levels of time intervals/SOAs (plus minus 750, 250 and 500, and 0ms), resulting in me creating my experiment in such a manner (see attached picture).

One set of fixation_cross and VA_750ms (for example) constitutes a block. Hence, in total, there are 7 blocks here (only 4 are pictured though). I have already randomized the trials within each block. The next step for me is to randomize the presentation of these blocks, with one block denoting one level of SOA/time interval (e.g +750ms). To do this, I’ve placed a loop around all the blocks, with this loop titled “blocknames” in the picture. While the experiment still works fine, randomization still doesn’t occur.

I understand that there was a post addressing the randomization of blocks, but I felt that it was more specific to experiments that only have one routine. This is not very feasible for my case considering that I would have to vary the time interval between two numerical stimuli within a trial.

What did you try to make it work?: Nevertheless, I’ve tried to create an excel file with the names of the excel files in each condition - across all routines, the excel files actually contain the same information, but they’re just named differently according to what the condition name is (e.g AV500ms, VA750ms). In this case, the experiment still works, but the blocks are still not being randomized.

What specifically went wrong when you tried that?: With the same excel file, I also tried to label my conditions as $condsFile instead of using the exact document location, but this was what I got instead.

At the same time, I was wondering if I could incorporate my SOA/time interval levels into Excel instead - how would this be carried out in Builder?

This might be some useful background info on my Psychopy software and laptop. OS (e.g. Win10): Win 10 PsychoPy version (e.g. 1.84.x): 2020.1.3 Standard Standalone? (y/n) Yes,

I apologize if this might have been posted a few times. However, I’ve tried to apply these solutions according to what my experiment requires, but to no avail. I’m also quite a new user to Psychopy and am not very sure on how to proceed from here as well. Would really appreciate any advice on this!

Answer 1

This isn't really a programming question per se, as it can be addressed entirely by using the graphical Builder interface of PsychoPy. In the future, you should probably address such questions to the dedicated support forum at https://discourse.psychopy.org rather than here at Stack Overflow.

In essence, your experiment should have a much simpler structure. Embed your two trial routines within a trials loop. After that loop, insert your break routine. Lastly, embed the whole lot within an outer blocks loop. i.e. your experiment will show only three routines and two loops, not the very long structure you currently have. The nested loops means the two trial routines will run on very trial, while the break routine will run only once per block.

The key aspect to controlling the block order is the outer blocks loop. Connect it to a conditions file that looks like this:

condition_file
block_1.csv
block_2.csv
block_3.csv
block_4.csv
block_5.csv
block_6.csv
block_7.csv

And set the loop to be be "random".

In the inner trials loop, put the variable name $condition_file in the conditions file field. So you now will have the order of blocks randomised across your subjects.

The other key aspect you need to learn is to control more of the task using variables contained within each of your conditions files. e.g. you are currently creating a separate routine for each ISI value (e.g. AV500ms and AV750ms). Instead, you should just have a single routine, called say AV. Make the timings of the stimulus components within that routine be controlled by a variable from your conditions file.

A key principle of programming is DRY: Don't Repeat Yourself (and although you aren't directly programming, under the hood, PsychoPy Builder will generate a Python program for you). Creating multiple routines that differ only in one respect is an indicator that things are not being specified optimally. By having only one routine, if you need to alter it in some way, you only have to do it once, rather than repeat it 7 times. The latter approach is very fragile and hard to maintain, and can easily lead to errors.

There is a resource on controlling blocks of trials here: https://www.psychopy.org/builder/blocksCounterbalance.html