# Stimulus Group Creation

**URL:** <https://mworks.discourse.group/t/stimulus-group-creation/316>\
**Category:** Support\
**Created:** [July 2, 2018, 7:32pm UTC](https://mworks.discourse.group/t/stimulus-group-creation/316 "2018-07-02T19:32:42Z")\
**Posts on this page:** 11\
**Page:** 1

<div class="post-metadata">

**Author:** ![cstawarz](https://yyz1.discourse-cdn.com/flex031/user_avatar/mworks.discourse.group/cstawarz/32/3_2.png) [@cstawarz](https://mworks.discourse.group/u/cstawarz)\
**Post date:** [July 2, 2018, 7:32pm UTC](https://mworks.discourse.group/t/stimulus-group-creation/316/1 "2018-07-02T19:32:42Z")

</div>

Hi Chris,

Quick question - We’ve done yet more modifications on how we want our code to work for the white noise experiment. We’ll generate images ahead of time, and we want to load a random set of these into a stimulus group for each trial. I’m working on how to do this - I need to generate a random number within the range of images we have for each frame we need, then use those numbers to get the image files (they will have the numbers in the names) into a stimulus group. However, I want the order to be random with no duplicate images, so I’m thinking a range replicator isn’t the way to do this. Any help would be appreciated.

Thanks!  
Yvonne

---

<div class="post-metadata">

**Author:** ![cstawarz](https://yyz1.discourse-cdn.com/flex031/user_avatar/mworks.discourse.group/cstawarz/32/3_2.png) [@cstawarz](https://mworks.discourse.group/u/cstawarz)\
**Post date:** [July 3, 2018, 2:04pm UTC](https://mworks.discourse.group/t/stimulus-group-creation/316/2 "2018-07-03T14:04:00Z")

</div>

Hi Yvonne,

> I need to generate a random number within the range of images we have for each frame we need, then use those numbers to get the image files (they will have the numbers in the names) into a stimulus group. However, I want the order to be random with no duplicate images, so I’m thinking a range replicator isn’t the way to do this.

There’s no getting around using a range replicator to define the set of `image_file` stimuli (well, unless you want to declare all 60-plus of them individually). However, there’s no need to use a range replicator to load images in to these stimuli. For example, in the `update_dynamic_white_noise` macro I wrote, I use a [while action](https://mworks.github.io/documentation/latest/components/repeat_actions_while.html) to unload and load image files:

```
frame_number = 0
while (frame_number < num_noise_frames) {
    unload_stimulus (dynamic_white_noise_frames[frame_number])
    dynamic_white_noise_frame_path = dynamic_white_noise_filenames[frame_number]
    load_stimulus (dynamic_white_noise_frames[frame_number])
    frame_number += 1
}

```

But you can load/unload the members of the stimulus group in any order you like. You don’t have to do it sequentially.

To prevent loading duplicate images, you’ll need some way to keep track of which ones you’ve already loaded. Within a single session, you might be able to use a [selection variable](https://mworks.github.io/documentation/latest/components/selection_variable.html) for this task. However, if you need to keep track of already-loaded images across multiple loads/unloads of the experiment, you’ll need to record the list of used images externally (maybe in a text file, written via Python actions).

Out of curiosity, why do you need to randomize the order of random noise images? Shouldn’t the randomness of the noise be enough?

Chris

---

<div class="post-metadata">

**Author:** ![cstawarz](https://yyz1.discourse-cdn.com/flex031/user_avatar/mworks.discourse.group/cstawarz/32/3_2.png) [@cstawarz](https://mworks.discourse.group/u/cstawarz)\
**Post date:** [July 5, 2018, 3:46pm UTC](https://mworks.discourse.group/t/stimulus-group-creation/316/3 "2018-07-05T15:46:23Z")

</div>

Hi Chris,

This is great, thank you. I’ll try this out.

The thought behind doing it randomly was so that we wouldn’t have to worry  
about keeping track of where we stopped after a session/day/load/unload of  
the experiment. Additionally, if we ran through all the images we  
generated, if we were doing this sequentially, we would want to shuffle  
them afterwards (or generate a new batch). But with picking them randomly  
each time, we won’t ever need to shuffle them. It was more about the  
stimulus/file management than the randomness in this case. Our other  
thought was using a “pointer” method, but because it’s not easy to  
save/retrieve variables from a text file with MWorks, we thought this might  
be easier on that front as well.

Best,  
Yvonne

---

<div class="post-metadata">

**Author:** ![cstawarz](https://yyz1.discourse-cdn.com/flex031/user_avatar/mworks.discourse.group/cstawarz/32/3_2.png) [@cstawarz](https://mworks.discourse.group/u/cstawarz)\
**Post date:** [July 6, 2018, 7:24pm UTC](https://mworks.discourse.group/t/stimulus-group-creation/316/4 "2018-07-06T19:24:49Z")

</div>

Hi Chris,

I’m having quite a few issues with getting this code written and would be  
thankful for some more help. Sorry about all the back and forth!

First, is there a way to use a variable for the file path to define a  
stimulus group? It didn’t work for us, though I notice you do this in the  
code that generates images in between each trial.

Second, for randomly pulling from a large bank of images, we thought  
perhaps the way to do it would be to redefine the stimulus group each trial  
using the image files that match the random numbers we generated. However,  
we ran into the fact that we can’t have a stimulus group inside of a  
protocol (even when within a macro). We also tried introducing the random  
subset during the loading phase (after putting more images than necessary  
in the stimulus group), which sort of worked, but because it’s a frame  
list, it ended up only presenting the ones that were loaded, and leaving  
gaps of gray background when images weren’t loaded.

I think I might need an example of how to do the following, because I’m  
totally unsure what to try next: Out of a large set of images  
(pre-generated, in a given folder and named sequentially such as  
white\_noise\_1, white\_noise\_2, etc.), before each trial we need to choose  
some number of images equal to the frames we want to present, define them  
as frame list stimuli, and then present them during the trial. I think I  
mentioned before that we don’t want repeated images, but we actually don’t  
care if they’re repeated or not.

Thank you,  
Yvonne

---

<div class="post-metadata">

**Author:** ![cstawarz](https://yyz1.discourse-cdn.com/flex031/user_avatar/mworks.discourse.group/cstawarz/32/3_2.png) [@cstawarz](https://mworks.discourse.group/u/cstawarz)\
**Post date:** [July 9, 2018, 3:32pm UTC](https://mworks.discourse.group/t/stimulus-group-creation/316/5 "2018-07-09T15:32:54Z")

</div>

Hi Yvonne,

I think the attached example does what you want. Please read the comments in the experiment before trying to run it. If you have any questions, please let me know.

Chris

---

<div class="post-metadata">

**Author:** ![cstawarz](https://yyz1.discourse-cdn.com/flex031/user_avatar/mworks.discourse.group/cstawarz/32/3_2.png) [@cstawarz](https://mworks.discourse.group/u/cstawarz)\
**Post date:** [July 9, 2018, 3:32pm UTC](https://mworks.discourse.group/t/stimulus-group-creation/316/6 "2018-07-09T15:32:54Z")

</div>

Attachment: [randomized\_batch\_loading.zip](https://mworks.discourse.group/uploads/short-url/m9bAmSkxDz7x0zrg9LPdWqeS7SP.zip) (1.75 KB)

---

<div class="post-metadata">

**Author:** ![cstawarz](https://yyz1.discourse-cdn.com/flex031/user_avatar/mworks.discourse.group/cstawarz/32/3_2.png) [@cstawarz](https://mworks.discourse.group/u/cstawarz)\
**Post date:** [July 9, 2018, 9:15pm UTC](https://mworks.discourse.group/t/stimulus-group-creation/316/7 "2018-07-09T21:15:09Z")

</div>

Hi Chris,

Thank you so much, this works great!! I’ll work on integrating it with the  
task code I have and let you know if I have issues.

I have a couple of quick questions as well. First, is there any way to get  
python files not to run at experiment load? This isn’t a huge issue, but I  
was having a python bridge write some things to a text file and ended up  
with an extra file that was produced at experiment runtime.  
Second, we changed the random number generation so that it also saves the  
numbers it generates as elements in an array (to write it to a text file  
for later use), but I wanted to double check that the array does get  
written in the order that the numbers are generated, so that we don’t  
confuse the order of the images.

Thank you,  
Yvonne

---

<div class="post-metadata">

**Author:** ![cstawarz](https://yyz1.discourse-cdn.com/flex031/user_avatar/mworks.discourse.group/cstawarz/32/3_2.png) [@cstawarz](https://mworks.discourse.group/u/cstawarz)\
**Post date:** [July 11, 2018, 12:23pm UTC](https://mworks.discourse.group/t/stimulus-group-creation/316/8 "2018-07-11T12:23:09Z")

</div>

Hi Yvonne,

> First, is there any way to get python files not to run at experiment load?

Sure. Replace

```
python_file ('create_symlink_to_noise_images.py')

```

with

```
resource ('create_symlink_to_noise_images.py')

```

Then, somewhere in your protocol, add

```
run_python_file ('create_symlink_to_noise_images.py')

```

Note that this will execute the file every time the protocol runs. If you still want it to run only once, you’ll need to handle that yourself (e.g. with a flag variable).

> Second, we changed the random number generation so that it also saves the numbers it generates as elements in an array (to write it to a text file for later use), but I wanted to double check that the array does get written in the order that the numbers are generated, so that we don’t confuse the order of the images.

I’m not sure what your question is here.

Chris

---

<div class="post-metadata">

**Author:** ![cstawarz](https://yyz1.discourse-cdn.com/flex031/user_avatar/mworks.discourse.group/cstawarz/32/3_2.png) [@cstawarz](https://mworks.discourse.group/u/cstawarz)\
**Post date:** [July 11, 2018, 2:35pm UTC](https://mworks.discourse.group/t/stimulus-group-creation/316/9 "2018-07-11T14:35:38Z")

</div>

Hi Chris,

Thanks! That’s perfect, I just wanted the python file in question to not  
run at load time.

The question about the arrays is more of a double check than anything, it’s  
a little bit of a silly question but is important to us. We’ve modified the  
code you gave me so that it writes the random numbers it generates to  
choose the images to an array:

random\_num\_noise\_images[frame\_number] = disc\_rand(1, total\_num\_noise\_images)

Which we then load with

noise\_frame\_path = format(

```
               'whitenoise_images/imgWhiteNoise_%d.tiff',

                random_num_noise_images[frame_number]

                )

```

> ```
> load_stimulus (white_noise_frames[frame_number])
> 
> ```

I just wanted to make sure that the numbers in the array get stored in the  
same order that we’ll load them in. That is, that the first number in the  
array corresponds to frame 1, the second to frame 2, etc. I know this is  
probably true, but I couldn’t figure out a way to verify it so I thought I  
would ask just in case MWorks organizes arrays differently than I would  
expect.

Thanks,  
Yvonne

---

<div class="post-metadata">

**Author:** ![cstawarz](https://yyz1.discourse-cdn.com/flex031/user_avatar/mworks.discourse.group/cstawarz/32/3_2.png) [@cstawarz](https://mworks.discourse.group/u/cstawarz)\
**Post date:** [July 13, 2018, 1:51pm UTC](https://mworks.discourse.group/t/stimulus-group-creation/316/10 "2018-07-13T13:51:23Z")

</div>

Hi Yvonne,

> I just wanted to make sure that the numbers in the array get stored in the same order that we’ll load them in. That is, that the first number in the array corresponds to frame 1, the second to frame 2, etc.

If the code looks like this:

```
frame_number = 0
while (frame_number < num_noise_frames) {
    unload_stimulus (white_noise_frames[frame_number])
    random_num_noise_images[frame_number] = disc_rand(1, total_num_noise_images)
    noise_frame_path = format(
        'whitenoise_images/white_noise_%d.tiff',
        random_num_noise_images[frame_number]
        )
    load_stimulus (white_noise_frames[frame_number])
    frame_number += 1
}

```

then, yes, the numbers in `random_num_noise_images` will be in the same order as the corresponding images in `white_noise_frames` are loaded.

Chris

---

<div class="post-metadata">

**Author:** ![cstawarz](https://yyz1.discourse-cdn.com/flex031/user_avatar/mworks.discourse.group/cstawarz/32/3_2.png) [@cstawarz](https://mworks.discourse.group/u/cstawarz)\
**Post date:** [July 19, 2022, 9:43pm UTC](https://mworks.discourse.group/t/stimulus-group-creation/316/11 "2022-07-19T21:43:53Z")

</div>