Request for Assistance with MWorks

Support
1

Hello Chris,

Good morning.

I’m Apaala, a new postdoc in Yasmine El-Shamayleh’s lab at Columbia. I’m developing a new behavioral task in MWorks and was hoping to get your advice on the best way to structure and load a relatively large stimulus set in MWEL.

Task Basics

On each trial, the task presents a single image (.jpg) from one of two main stimulus categories, A or B. Each category contains multiple stimulus variants, and for a given session we would like to be able to select an arbitrary subset of those variants and sample images only from the selected groups. The number of variants and the number of images within each variant may differ.

Current Data Structure

Right now, I am not using a hierarchical/tree-style directory structure for the task images. I currently have a single parent folder containing multiple stimulus folders at the same level, for example:

Task_images/
├── A/
│   ├── A_1.jpg
│   ├── A_2.jpg
│   └── ...
├── B/
│   ├── B_1.jpg
│   ├── B_2.jpg
│   └── ...
├── B2/
│   ├── B2_1.jpg
│   ├── B2_2.jpg
│   └── ...
├── B3/
│   ├── B3_1.jpg
│   ├── B3_2.jpg
│   └── ...
└── ...

So at the moment, A, B, B2, B3, etc. are all separate folders under the same parent directory.

For a given session, I would ideally like to be able to activate an arbitrary subset of these folders.

Current MWEL Implementation

Right now, I define a separate stimulus_group for each folder and use a range_replicator to instantiate the individual image_file stimuli:

%define total_images_in_folder = 14

stimulus_group A_Images {
    range_replicator (
        variable = A_counter
        from = 1
        to = total_images_in_folder
        step = 1
    ) {
        image_file A_image_${A_counter} (
            path = 'Task_images/A/A_${A_counter}.jpg'
            x_size = stimulus_display_size
            y_size = stimulus_display_size
            x_position = stimulus_x
            y_position = stimulus_y
            announce_load = false
        )
    }
}

I currently have 14 images in each folder and repeat this pattern for A, B, B2, B3, etc.

At runtime, I separately control which image indices are active through GUI variables. The task selects the stimulus folder/category and the image index independently, and those selections are combined at the end to index the appropriate stimulus_group.

This works, but it requires me to manually duplicate the MWEL structure for every folder, and the number of images in each folder is currently hard-coded.

Questions

1). Would a tree/hierarchical data structure be a better way to organize the image folders?
For example, would it make more sense to reorganize the stimulus library as something like:

Task_images/

├── A/

│   ├── A1/
│   ├── A2/
│   └── ...
└── B/
    ├── B1/
    ├── B2/
    └── ...

and then represent the stimulus selection as something like category → variant → image? Or is there another data structure/pattern in MWEL that would scale better than either of these approaches?

2). Can the MWEL dynamically determine the contents of a directory?

Currently, range_replicator requires me to specify total_images_in_folder. Is there a supported way to enumerate files in a directory, or otherwise determine the number of available images at load/parse time? Ideally, the folders could contain different numbers of images without requiring a separate hard-coded count for each one.

3). Is there a cleaner way to select active stimulus folders at runtime?

Ideally, I would like the GUI or session configuration to specify something equivalent to:
active_groups = [A, B2, B5], and have the trial logic sample only from the images belonging to those groups. Is there an MWEL/MWorks pattern you would recommend for this instead of maintaining many separate stimulus_groups and selection branches?

4). Can stimulus categories be represented differently in the Eye Monitor?

Is there a way to assign different visual properties to stimulus announcements in the MWorks Eye Monitor based on the group/category? For example, could stimuli from category A versus category B be displayed with different colors or markers in the Eye Monitor.

My main concern is scalability and maintainability. The current implementation works, but as the number of stimulus folders increases, I want to avoid duplicating a large amount of MWEL code if there is a more appropriate MWorks-native way to structure it.

Thanks so much in advance for your help!

Apaala

5

Hi Apaala,

Would a tree/hierarchical data structure be a better way to organize the image folders?

Unfortunately, MWorks doesn’t support creating nested stimulus groups using replicators. You can organize your files in a tree if you like, but you’ll still be restricted to a single level of stimulus groups in the experiment.

Can the MWEL dynamically determine the contents of a directory?

Yes, you can do this with a list replicator and the filenames directive. For example:

stimulus_group A_Images {
    list_replicator (
        variable = A_path
        values = 'filenames(Task_images/A/*.jpg)'
        ) {
        image_file ${A_path} (
            path = ${A_path}
            x_size = stimulus_display_size
            y_size = stimulus_display_size
            x_position = stimulus_x
            y_position = stimulus_y
            announce_load = false
            )
    }
}

You can get the number of images in the directory using the filenames function:

var num_A_Images = size(filenames('Task_images/A/*.jpg'))

Is there a cleaner way to select active stimulus folders at runtime?

This is a little tricky. Let me think about it and put together an example.

Can stimulus categories be represented differently in the Eye Monitor?

No, that isn’t possible at present.

Cheers,
Chris