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Edit stimuli.md to reflect the spec more completely
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# Stimuli

Stimulus files should be stored in the `/stimuli` directory under the root directory of the dataset. The `/stimuli` directory can contain subdirectories to organize the stimulus files. Stimulus files SHOULD follow the BIDS naming conventions and SHOULD be referenced in the `events.tsv` file using the `stim_id` column. The `stim_id` column represents unique identifiers for the stimuli. Additional information about the stimuli and their annotations can be provided in the `stimuli.tsv`, `stimuli.json`, `annotations.tsv`, `annotations.json`, and `stim-<label>.json` files.
## Stimulus Files Organization

Standardizing stimulus files and their annotations within the BIDS specifications offers several advantages:
Stimulus files MUST be stored in the `/stimuli` directory under the root directory of the dataset.
The `/stimuli` directory can contain subdirectories to organize the stimulus files.
Stimulus files MUST follow the BIDS naming conventions and SHOULD be referenced in the `events.tsv`
file using the `stim_id` column.

1. **Consistency**: Ensures that stimulus files are stored and referenced consistently across different datasets.
2. **Reusability**: Facilitates the reuse of stimulus files and annotations in other studies by providing a standardized structure.
3. **Efficiency**: Reduces redundancy by avoiding the need to replicate annotations across subjects, modalities, tasks, and runs.
4. **Flexibility**: Allows for easy modification of annotations by updating a single file, enabling the reuse of datasets with alternative annotations.
The standardization of stimulus files and their annotations within BIDS offers several key benefits:

1. **Consistency**: Ensures uniform storage and referencing across datasets
2. **Reusability**: Enables stimulus reuse across studies through standardized structure
3. **Efficiency**: Minimizes redundancy by centralizing annotations
4. **Flexibility**: Facilitates dataset reuse with alternative annotations

To preserve backward compatibility with existing datasets (see the Legacy section below), the use of these specifications for `/stimuli` directory and the `stim_id` column in the `events.tsv` files is RECOMMENDED but not required. Researchers are encouraged to follow these guidelines to enhance the interoperability and reproducibility of their studies.

Following these guidelines will help ensure that stimulus files and their annotations are stored and referenced consistently across different datasets, facilitating data sharing, reuse, and reproducibility.

## File Organization

<!-- This block generates a file tree.
A guide for using macros can be found at
https://github.com/bids-standard/bids-specification/blob/master/macros_doc.md
Expand All @@ -21,8 +28,8 @@ A guide for using macros can be found at
"stimuli": {
"stimuli.tsv": "",
"stimuli.json": "",
"[stim-<label>[_part-<label>]_<suffix>.<extension>]": "",
"[stim-<label>[_part-<label>]_<suffix>.json]": "",
"[stim-<label>[_part-<label>]<suffix>.<extension>]": "",
"[stim-<label>[_part-<label>]<suffix>.json]": "",
"[[stim-<label>_]annotations.tsv]": "",
"[[stim-<label>_]annotations.json]": "",
"[stim-<label>[_part-<label>]_annot-<label>_events.tsv]": "",
Expand All @@ -32,50 +39,20 @@ A guide for using macros can be found at

Note: The presence of `stimuli.tsv` file indicates that the content of the `/stimuli` folder follows this BIDS specification for stimulus organization. This structure is planned to become mandatory in BIDS 2.0.

## Referencing Stimulus Identifiers in `events.tsv`

To reference stimulus identifiers in the `events.tsv` file, use the `stim_id` column. The values in the `stim_id` column should represent unique identifiers for the stimuli. Stimulus ID (`stim_id`) should correspond to the unique identifier of the stimulus file in the /stimuli directory and expands to all files (both stimulus and annotation files) that share the same stimulus ID.

Example `events.tsv` file:

| onset | duration | trial_type | response_time | stim_id |
|-------|----------|------------|---------------|---------|
| 1.23 | 0.65 | start | 1.435 | stim-\<label\> |
| 5.65 | 0.65 | stop | 1.739 | stim-\<label\> |
| 12.1 | 2.35 | n/a | n/a | stim-\<label\> |

In the accompanying JSON sidecar, the `stim_id` column might be described as follows:

```JSON
{
"stim_id": {
"LongName": "Stimulus identifier",
"Description": "Represents a unique identifier for the stimulus presented at the given onset time."
}
}
```

## The stimulus file and JSON sidecar

Stimulus files can be of various types including audio, image, video, and combined audiovideo formats. Each stimulus file SHOULD have an accompanying JSON sidecar file containing metadata about the stimulus. The structure of the stimulus file name and the JSON sidecar file name SHOULD follow the BIDS naming conventions as below:
### Stimulus File Formats

- Stimulus file: `stim-<label>[_part-<label>]_<suffix>.<extension>`
- JSON sidecar file: `stim-<label>[_part-<label>]_<suffix>.json`
The following table lists the supported stimulus file formats and their corresponding suffixes. The suffixes are used to identify the type of stimulus file and are appended to the `stim-<label>` prefix in the file name.

Then stimulus file names MUST start with `stim-` followed by a unique label, and an optional part label if the stimulus is divided into parts. `stim-` is the standard entity for the stimulus files, indicating that the files do not belong to a specific subject or participant but rather are likely to be used across subjects throughout the experiment. The suffix SHOULD describe the type of stimulus (such as audio, image, video, audiovideo) and the extension MUST indicate the file format. The JSON sidecar file MUST have the same name as the stimulus file but with a `.json` extension. Here are the allowed suffixes and extensions for the stimulus files:
| **suffix** | **extensions** | **description** |
|-------------|-------------------------|-----------------------------------|
| audio | `.wav`, `.mp3`, `.aac`, `.ogg` | Audio-only stimulus files |
| image | `.jpg`, `.png`, `.svg` | Static visual stimulus files |
| video | `.mp4`, `.avi`, `.mkv`, `.webm` | Video-only stimulus files |
| audiovideo | `.mp4`, `.avi`, `.mkv`, `.webm` | Combined audio-visual files |

| Modality | Extensions | Description |
|--------------|---------------------------|------------------------------------|
| `audio` | .wav, .mp3, .aac, .ogg | Audio-only stimulus files |
| `image` | .jpg, .png, .svg | Static visual stimulus files |
| `video` | .mp4, .avi, .mkv, .webm | Video-only stimulus files |
| `audioVideo` | .mp4, .avi, .mkv, .webm | Combined audio-visual stimulus files |
<!-- | Tactile | .ros | Robot Operating System program files for tactile stimulation | -->

If distribution restrictions prevent including the actual stimulus file, the JSON sidecar SHOULD still be present with appropriate metadata describing the stimulus.
For the stimuli that can be described in a table format (such as image datasets), the `stimuli.tsv` and `stimuli.json` files can be used to provide information about the stimuli based on their `stim_id`, and the presence of the stimulus file and JSON sidecar is OPTIONAL.

The following table describes the REQUIRED, RECOMMENDED, and OPTIONAL fields for the `stim-<label>.json` file:
## Stimulus description (`stim-<label>_<suffix>.json`)
The `stim-<label>_<suffix>.json` file provides metadata about the *singular* stimulus file.
The following fields are defined to describe the stimulus file:

<!-- This block generates a metadata table.
These tables are defined in
Expand All @@ -87,11 +64,22 @@ A guide for using macros can be found at
-->
{{ MACROS___make_sidecar_table("stimulus.Stimulus") }}

## Stimuli.tsv and Stimuli.json
In some cases, such as observing the copyright of a stimulus file, the actual stimulus file may not be shared. In such cases, the `stim-<label>_<suffix>.json` file SHOULD be used to provide metadata about the stimulus file, including the license, copyright, URL, and description.

The `stimuli.tsv` and `stimuli.json` files are used to provide information about the stimuli based on their `stim_id`. This file is similar in usage as `participants.tsv`, `scans.tsv` and `sessions.tsv`, which list descriptions about subjects, scans and sessions, respectively. The `stimluli.tsv/json` files should be placed in the `/stimuli` directory.
### Example `stim-<label>_<suffix>.json`

```JSON
{
"License": "CC-BY-4.0",
"Copyright": "Lab 2023",
"URL": "https://example.com/stimuli/",
"Description": "Collection of face images, tones, and movie clips used in the experiment"
}
```

### Stimuli.tsv
## Stimuli Description (`stimuli.tsv`)

The `stimuli.tsv/json` files are used to provide information about the stimuli based on their `stim_id`. This file is similar in usage as `participants.tsv`, `scans.tsv` and `sessions.tsv`, which list descriptions about subjects, scans and sessions, respectively. The `stimluli.tsv/json` files MUST be placed in the `/stimuli` directory.

The `stimuli.tsv` file contains information about each stimulus, including stimulus ID, type, URL, and other relevant details. The following table describes the REQUIRED, RECOMMENDED, and OPTIONAL columns for the `stimuli.tsv` file:

Expand All @@ -103,36 +91,69 @@ and a guide for using macros can be found at
-->
{{ MACROS___make_columns_table("stimuli.Stimuli") }}

This is an example of the `stimuli.tsv` file describing three images from the natural scene dataset (NSD):
### Example `stimuli.tsv`

| stimulus_id | type | description | HED | NSD_id | COCO_id |
|--------------|-------|-------------|-----|--------|---------|
| stim-nsd02951 | image | an open market full of people and piles of vegetables | ((Item-count, High), Ingestible-object), (Background-view, ((Human, Body, Agent-trait/Adult), Outdoors, Furnishing, Natural-feature/Sky, Urban, Man-made-object)) | 2951 | 262145 |
| stim-nsd02991 | image | a couple of people are cooking in a room | (Foreground-view, ((Item-count/1, (Human, Body, Agent-trait/Adult)), (Item-count/1, (Human, Body, (Face, Away-from), Male, Agent-trait/Adult)), ((Item-count, High), Furnishing))), (Background-view, (Ingestible-object, Furnishing, Room, Indoors, Man-made-object, Assistive-device)) | 2991 | 262239 |
| stim-nsd03050 | image | a person standing on a surfboard riding a wave | (Foreground-view, ((Item-count/1, ((Human, Human-agent), Body, Male, Agent-trait/Adolescent)), (Play, (Item-count/1, Man-made-object)))), (Background-view, (Outdoors, Natural-feature/Ocean)) | 3050 | 262414 |
```Text
stimulus_id type URL license copyright description present
stim-face01 image https://example.com/faces/face01.jpg CC-BY-4.0 Lab 2023 A female face with neutral expression true
stim-tone01 audio https://example.com/tones/tone01.wav CC-BY-4.0 Lab 2023 A 440Hz pure tone true
stim-movie01 video https://example.com/movies/movie01.mp4 n/a Studio XYZ A clip from copyrighted movie false
```

### Stimuli.json
The `stimuli.json` file provides detailed descriptions of the columns in the `stimuli.tsv` file. There MAY be extra entries in the `stimuli.json` in addition to the columns in the `stimuli.tsv` to provide more details about the stimulus.

The `stimuli.json` file provides detailed descriptions of the columns in the `stimuli.tsv` file. There can be extra entries in the `stimuli.json` in addition to the columns in the `stimuli.tsv` to provide more details about the stimulus.
In cases where the stimulus is not shared, the `stimuli.tsv` file can be used to provide metadata about the stimuli, including the license, copyright, URL, and description. This is simialr to the use of `stim-<label>_<suffix>.json` files for individual stimuli files. In the case of conflict between the metadata in the `stimuli.tsv` and `stim-<label>_<suffix>.json` files, the metadata in the `stim-<label>_<suffix>.json` file takes precedence.

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## Annotations.tsv and Annotations.json
## Stimulus Annotations
Annotations of the still images or general description of the stimuli (such as frequency and duration of a beep sound) can be stored in the `stimuli.tsv` as an additional column or `stim-<label>_<suffix>.json` as described above. Here is an example of how annotations can be stored in the `stimuli.tsv` file for an image from the Natural Scene Dataset (NSD):

The `annotations.tsv` and `annotations.json` files are used to provide additional information about the annotations associated with the stimuli. These files should be placed in the `/stimuli` directory.
| stimulus_id | type | description | HED | NSD_id | COCO_id |
|--------------|-------|-------------|-----|--------|---------|
| stim-nsd02951 | image | an open market full of people and piles of vegetables | ((Item-count, High), Ingestible-object), (Background-view, ((Human, Body, Agent-trait/Adult), Outdoors, Furnishing, Natural-feature/Sky, Urban, Man-made-object)) | 2951 | 262145 |

### Annotations.tsv
However, for time-varying stimuli, such as audio or video, it is RECOMMENDED to use specific annotations files in the form of `stim-<label>_annot-<label>_events.tsv/json` to store the annotations. These files have the same structure as the `events.tsv/json` files and are used to store annotations for the stimuli. There can be multiple annotation files for a single stimulus file, each with a unique annotation label. The annotation files MUST be stored in the `/stimuli` directory.

The `annotations.tsv` file contains information about each annotation, including the annotation ID and description. The following table describes the REQUIRED, RECOMMENDED, and OPTIONAL columns for the `annotations.tsv` file:
## Annotation Description (`annotations.tsv`)

The `annotations.tsv` file contains additional metadata about stimulus annotations. There MAY be a single `annotations.tsv` file for all the stimuli or separate `stim-<label>_annotations.tsv` files for each stimulus.
The following columns are defined for the `annotations.tsv` file:

<!-- This block generates a columns table.
The definitions of these fields can be found in
src/schema/rules/tabular_data/*.yaml
and a guide for using macros can be found at
https://github.com/bids-standard/bids-specification/blob/master/macros_doc.md
-->
{{ MACROS___make_columns_table("annotations.Annotations") }}
{{ MACROS___make_columns_table("stimuli.Annotations") }}

### Example `*_annotations.tsv`

### Annotations.json
```Text
annot_id description
face01_emo Emotion annotation for face01 stimulus
face01_gen Gender annotation for face01 stimulus
face01_age Age group annotation for face01 stimulus
```

The `annotations.json` file provides detailed descriptions of the columns in the `annotations.tsv` file.
## Referencing Stimulus Identifiers in `events.tsv`

There could be only one `annotations.tsv` in the `/stimuli` directory. Alternatively, each stimulus (with a unique stimulus ID) can have a separate `stim-<label>_annotations.tsv` to describe the annotations for a specific stimulus.
To reference stimulus identifiers in the `events.tsv` file, use the `stim_id` column. The values in the `stim_id` column should represent unique identifiers for the stimuli. Stimulus ID (`stim_id`) should correspond to the unique identifier of the stimulus file in the /stimuli directory and expands to all files (both stimulus and annotation files) that share the same stimulus ID.

Example `events.tsv` file:

| onset | duration | trial_type | response_time | stim_id |
|-------|----------|------------|---------------|---------|
| 1.23 | 0.65 | start | 1.435 | `stim-<label>` |
| 5.65 | 0.65 | stop | 1.739 | `stim-<label>` |
| 12.1 | 2.35 | n/a | n/a | `stim-<label>` |

In the accompanying JSON sidecar, the `stim_id` column might be described as follows:

```JSON
{
"stim_id": {
"LongName": "Stimulus identifier",
"Description": "Represents a unique identifier for the stimulus presented at the given onset time."
}
}
```

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