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Task events

The purpose of this file is to describe timing and other properties of events recorded during a run. Events are, for example, stimuli presented to the participant or participant responses (see Definitions). A single event file MAY include any combination of stimulus, response, and other events. Events MAY overlap in time. Please mind that this does not imply that only so called "event related" study designs are supported (in contrast to "block" designs) - each "block of events" can be represented by an individual row in the events.tsv file (with a long duration).

Template:

sub-<label>/[ses-<label>]
    <data_type>/
        <matches>_events.tsv
        <matches>_events.json

Where <matches> corresponds to task filename. For example: sub-control01_task-nback.

Each task events file REQUIRES a corresponding task data file. It is also possible to have a single events.tsv file describing events for all participants and runs (see Inheritance Principle). As with all other tabular data, events.tsv files MAY be accompanied by a JSON file describing the columns in detail (see Tabular Files).

The tabular files consists of one row per event and a set of REQUIRED and OPTIONAL columns:

Column name Requirement Level Data type Description
onset REQUIRED number Onset (in seconds) of the event, measured from the beginning of the acquisition of the first data point stored in the corresponding task data file. Negative onsets are allowed, to account for events that occur prior to the first stored data point. For example, in case there is an in-scanner training phase that begins before the scanning sequence has started events from this sequence should have negative onset time counting down to the beginning of the acquisition of the first volume.
If any data points have been discarded before forming the data file (for example, "dummy volumes" in BOLD fMRI), a time of 0 corresponds to the first stored data point and not the first acquired data point.
duration REQUIRED number or "n/a" Duration of the event (measured from onset) in seconds. Must always be either zero or positive (or n/a if unavailable). A "duration" value of zero implies that the delta function or event is so short as to be effectively modeled as an impulse.
sample OPTIONAL integer Onset of the event according to the sampling scheme of the recorded modality (that is, referring to the raw data file that the events.tsv file accompanies).
trial_type OPTIONAL string Primary categorisation of each trial to identify them as instances of the experimental conditions. For example: for a response inhibition task, it could take on values go and no-go to refer to response initiation and response inhibition experimental conditions.
response_time OPTIONAL number or "n/a" Response time measured in seconds. A negative response time can be used to represent preemptive responses and n/a denotes a missed response.
value OPTIONAL number or string Marker value associated with the event (for example, the value of a TTL trigger that was recorded at the onset of the event).
HED OPTIONAL string Hierarchical Event Descriptor (HED) Tag. See Appendix III for details.

5 Note for MRI data: If any acquired scans have been discarded before forming the imaging data file, ensure that an onset of 0 corresponds to the time the first image was stored. For example in case there is an in scanner training phase that begins before the scanning sequence has started events from this sequence should have negative onset time counting down to the beginning of the acquisition of the first volume.

An arbitrary number of additional columns can be added. Those allow describing other properties of events that could be later referred in modelling and hypothesis extensions of BIDS. Note that the trial_type and any additional columns in a TSV file SHOULD be documented in an accompanying JSON sidecar file.

Example:

└─ sub-control01/
   └─ func/
      ├─ sub-control01_task-stopsignal_events.tsv 
      └─ sub-control01_task-stopsignal_events.json 

Example of the content of the TSV file:

onset   duration    trial_type  response_time   stim_file
1.23    0.65    start   1.435   images/red_square.jpg
5.65    0.65    stop    1.739   images/blue_square.jpg

In the accompanying JSON sidecar, the trial_type column might look as follows:

{
    "trial_type": {
        "LongName": "Event category",
        "Description": "Indicator of type of action that is expected",
        "Levels": {
            "start": "A red square is displayed to indicate starting",
            "stop": "A blue square is displayed to indicate stopping"
        }
    }
}

Note that all other columns SHOULD also be described but are omitted for the sake of brevity.

For multi-echo files, the events.tsv file is applicable to all echos of a particular run:

└─ sub-01/
   └─ func/
      ├─ sub-01_task-cuedSGT_run-1_events.tsv 
      ├─ sub-01_task-cuedSGT_run-1_echo-1_bold.nii.gz 
      ├─ sub-01_task-cuedSGT_run-1_echo-2_bold.nii.gz 
      └─ sub-01_task-cuedSGT_run-1_echo-3_bold.nii.gz 

Note: Events can also be documented in machine-actionable form using HED (Hierarchical Event Descriptor) tags. This type of documentation is particularly useful for datasets likely to be used in event-related analyses. See Hierarchical Event Descriptors for additional information and examples.

Stimuli

Additional information about the stimuli can be added in the events.tsv and events.json files.

This can be done by using a /stimuli directory or by reference to a stimuli database.

Stimuli directory

The stimulus files can be added in a /stimuli directory (under the root directory of the dataset; with optional subdirectories) AND using a stim_file column in events.tsv mentioning which stimulus file was used for a given event,

There are no restrictions on the file formats of the stimuli files, but they should be stored in the /stimuli directory.

Column name Requirement Level Data type Description
stim_file OPTIONAL string Represents the location of the stimulus file (such as an image, video, or audio file) presented at the given onset time. There are no restrictions on the file formats of the stimuli files, but they should be stored in the /stimuli directory (under the root directory of the dataset; with optional subdirectories). The values under the stim_file column correspond to a path relative to /stimuli. For example images/cat03.jpg will be translated to /stimuli/images/cat03.jpg.

Stimuli databases

References to existing databases can also be encoded using additional columns. The following example includes references to the Karolinska Directed Emotional Faces (KDEF) database.

Example:

└─ sub-control01/
   └─ func/
      ├─ sub-control01_task-emoface_events.tsv 
      └─ sub-control01_task-emoface_events.json 

Example of the content of the TSV file:

onset duration  trial_type  identifier  database  response_time
1.2 0.6 afraid  AF01AFAF  kdef  1.435
5.6 0.6 angry AM01AFAN  kdef  1.739
5.6 0.6 sad AF01ANSA  kdef  1.739

The trial_type and identifier columns from the events.tsv files might be described in the accompanying JSON sidecar as follows:

{
    "trial_type": {
        "LongName": "Emotion image type",
        "Description": "Type of emotional face from Karolinska database that is displayed",
        "Levels": {
            "afraid": "A face showing fear is displayed",
            "angry": "A face showing anger is displayed",
            "sad": "A face showing sadness is displayed"
        }
    },
    "identifier": {
        "LongName": "Karolinska (KDEF) database identifier",
        "Description": "ID from KDEF database used to identify the displayed image"
    }
}

Note that all other columns SHOULD also be described but are omitted for the sake of brevity.

Stimulus presentation details

It is RECOMMENDED to include details of the stimulus presentation software, when applicable:

Key name Requirement Level Data type Description
StimulusPresentation RECOMMENDED object Object containing key value pairs related to the software used to present the stimuli during the experiment, specifically: "OperatingSystem", "SoftwareName", "SoftwareRRID", "SoftwareVersion" and "Code". See table below for more information.

The object supplied for StimulusPresentation SHOULD include the following key-value pairs:

Key name Requirement Level Data type Description
Code RECOMMENDED string URI of the code used to present the stimuli. Persistent identifiers such as DOIs are preferred. If multiple versions of code may be hosted at the same location, revision-specific URIs are recommended.
OperatingSystem RECOMMENDED string Operating system used to run the stimuli presentation software (for formatting recommendations, see examples below this table).
SoftwareName RECOMMENDED string Name of the software that was used to present the stimuli.
SoftwareRRID RECOMMENDED string Research Resource Identifier of the software that was used to present the stimuli. Examples: The RRID for Psychtoolbox is 'SCR_002881', and that of PsychoPy is 'SCR_006571'.
SoftwareVersion RECOMMENDED string Version of the software that was used to present the stimuli.

The operating system description SHOULD include the following attributes:

  • type (for example, Windows, macOS, Linux)
  • distribution (if applicable, for example, Ubuntu, Debian, CentOS)
  • the version number (for example, 18.04.5)

Examples:

  • Windows 10, Version 2004
  • macOS 10.15.6
  • Linux Ubuntu 18.04.5

The amount of information supplied for the OperatingSystem SHOULD be sufficient to re-run the code under maximally similar conditions.

The information related to stimulus presentation might be described in the accompanying JSON sidecar as follows (based on the example of the previous section):

{
    "trial_type": {
        "LongName":   "Emotion image type",
        "Description": "Type of emotional face from Karolinska database that is displayed",
        "Levels": {
            "afraid": "A face showing fear is displayed",
            "angry":  "A face showing anger is displayed",
            "sad":    "A face showing sadness is displayed"
        }
    },
    "identifier": {
        "LongName": "Unique identifier from Karolinska (KDEF) database",
        "Description": "ID from KDEF database used to identify the displayed image"
    },
    "StimulusPresentation": {
        "OperatingSystem": "Linux Ubuntu 18.04.5",
        "SoftwareName": "Psychtoolbox",
        "SoftwareRRID": "SCR_002881",
        "SoftwareVersion": "3.0.14",
        "Code": "doi:10.5281/zenodo.3361717"
    }
}