Introduction¶

A task is an “instructed activity”: a set of goals to be achieved and actions to be performed, or a combination of the two, under conditions the experimenter controls, so that what participants do can be attributed to the mental processes the task was designed to engage.

What the catalog is for¶

Experiments in cognitive and behavioral neuroscience are built from a fairly small repertoire of standard tasks, but the datasets they produce rarely say which one was used in a way a machine can act on. This catalog provides a controlled vocabulary for that: a list of tasks, a list of the cognitive processes those tasks engage, and the links between them. Tagging a dataset with identifiers from the catalog makes it findable by task name, by alias, or by process, and makes datasets that share a task or a process comparable.

The catalog is being developed as part of HED (Hierarchical Event Descriptors), the standard for annotating what happened during an experiment. HED describes events; the task catalog describes the paradigm the events belong to. How task and process identifiers will be carried in HED annotations and in dataset metadata is not yet decided, and the identifiers here are not HED schema terms.

Tasks¶

A task in this catalog is a structured experimental paradigm that produces a sequence of discrete, time-stamped events, has a specific reproducible procedure, is widely used, and engages identifiable cognitive processes. Particular questionnaires, clinical screening instruments, generic labels such as “memory task”, and one-off designs are excluded. The full rules are in the Task selection criteria.

The catalog also has 3 pseudo tasks, which are not tasks in the sense above: the Rest Task, the Fixate Task and the Take Questionnaire Task. A pseudo task is a block that sets up or holds a brain state, or collects a self-report, rather than eliciting a process through trials. Such blocks appear in most experiments and datasets need to label them. The catalog includes them for that reason, marks them on their pages, and gives them no process links. The Pseudo tasks section of the task criteria says exactly what qualifies.

The catalog currently has 103 tasks. Each task page carries:

a canonical name and its aliases, so that a search for “CWIT” or “Stroop” lands on the Stroop Color-Word Task;
a short definition and a longer description;
an inclusion test in three parts: the procedure the participant follows, the manipulation the experimenter varies, and the measurement recorded. An experiment is an instance of the task when its procedure matches, it manipulates at least one of the listed variables, and it records at least one of the listed measures. The procedure is decisive: two experiments with the same procedure are the same task even if they target different constructs;
a list of variations, each with a description and a justification. A variation is a named version that changes what the participant experiences or does, so that the event structure of the recorded data differs. Changing the recording equipment, the analysis, the population or the stimulus set does not make a variation; changing the response modality, the stimulus-response mapping or the required actions does. There are 776 variations across the catalog;
the cognitive processes the task engages, linked to their definitions;
key references that established the paradigm and recent references that give a modern entry point;
where one exists, the corresponding Cognitive Atlas entry.

Paradigm families¶

Tasks are filed under 19 paradigm families by what the participant does: conflict and interference tasks, response inhibition tasks, recall and recognition tests, economic games, and so on. The Stroop Color-Word Task is in the family Conflict and interference tasks. A family is a browsing aid, not a claim about mechanism; the processes a task engages are the place to look for that. Every task is in exactly one family, and the assignment is a curation decision that is expected to change. The task index lists the families with their scope.

Cognitive processes¶

A cognitive process is a mental operation hypothesized to occur during a trial: something with an identifiable onset, an eliciting condition and an in-principle measurable signature. A candidate qualifies when it is plausible to say when in a trial it happens, what elicits it, and how it is measured. States and traits, specific emotions, stimulus categories, individual-difference constructs, task parameters, analysis methods and umbrella terms such as “attention” or “memory” are excluded; the umbrella role is carried by the categories instead. The full rules are in the process selection criteria.

The catalog has 172 processes in 19 categories. A category groups processes by research tradition for browsing and carries a scope statement and a note of what is out of scope. Each process page entry has a definition, aliases where the literature uses more than one name, fundamental and recent references, and the list of tasks that engage it. Some processes are engaged by no task in the current catalog; they are kept because they are real and the catalog may grow a task for them.

Links between tasks and processes¶

A task is linked to a process when the task’s inclusion test engages that process: the paradigm-defining papers say so, a standard condition contrast isolates it, or a standard measure indexes it. A link is not an ontology assertion and not a claim that the task engages nothing else; it records what the task is designed to probe. The task-process links page lists every link in both directions.

Identifiers¶

Every entity has a typed identifier, so an identifier met anywhere can be classified at sight:

Kind	Form	Example
Task	`hedtsk_<slug>`	`hedtsk_stroop_color_word`
Task variation	`hedvar_<task slug>__<variation slug>`	`hedvar_stroop_color_word__counting_stroop`
Process	`hed_<slug>`	`hed_response_inhibition`
Process category	`<slug>`	`inhibitory_control_and_conflict_monitoring`
Paradigm family	`<slug>`	`conflict_and_interference`

The hed_ prefix on process identifiers is the catalog’s working prefix and is not a claim of HED schema membership. Identifiers are provisional while the catalog is being curated; when they stabilise, renames will become aliases.

Where the catalog came from¶

The starting corpus was the Cognitive Atlas, a community-built ontology of cognitive concepts and the paradigms that measure them. Its task list was narrowed to paradigms that produce event-structured data, its concepts were reshaped into processes that pass the selection test above, and a gap analysis added paradigms the Atlas never registered. Every task and process here is mapped back to the Atlas entry by entry; the Cognitive Atlas pages describe the Atlas on its own terms, the relationship page says how the two resources differ, and the mapping method page says how each correspondence was decided.

Status¶

The catalog is a work in progress. Its lists are not definitive, its identifiers are provisional, and its curation is a continuing process. Suggestions, corrections and ideas should be posted as issues at https://github.com/hed-standard/hed-task/issues; the repository’s contributing guide describes the process, and how to use the catalog says what a useful proposal contains.