# Naming temporal variable

## Table of content

Numerous words refer to “time”; below we describe what those words mean for us.

Some names are used to designate specific points in time:

*_datetime
indicates a date and a time in a (somewhat) absolute sense for an event; datetime variables are expected to be in a specific format (see below). For example the start datetime of a timeline may be 2009-10-31T01:48:52.512Z.

We use *_datetime rather than * _date_time because date_time may suggest that time is a feature of the entity time rather than datetime being a single construct/feature of the entity it is appended to (e.g., start_datetime is less ambiguous than start_date_time which could be read as (start_)date_time or (start_date)_time).

*_timestamp
refers to the timing of an event but its reference may be relative (e.g., beginning of the session) and its format less specified (e.g., a duration expressed in seconds). Because of the referencing, “timestamp” may be more ambiguous; if it refers to a date and time, use *_datetime; if it refers to a duration relative to a particular reference, use a term that makes this reference more explicit (e.g., stimlus_onset instead of stimulus_timestamp).
*_onset
refers to the duration between the trial start and the start of some event (e.g., stimulus_onset);
*_offset
refers to the duration between the trial start and the end of some event (e.g., stimulus_offset);
*_time
ambiguous term we keep for historic reasons; we currently use it only for response_time.

A point in time may be seen as a duration relative to a reference point; in the examples above, the focus is on the event itself rather than on the duration.

Other names refer to the duration of an event itself (the onset and offset of the event itself).

duration
refers to the time difference between the end and the start of some entity; for example, stimulus_duration describes how long the stimulus was displayed;

Finally, still other names refer to the duration separating two specific events:

interval
refers to the time difference between the end of an entity and the start of another (typically, but not always of the same type).
For example inter_stimulus_interval is the duration between the disappearance of a stimulus and the appearance of the next one; cue_target_interval is the duration between the end of the cue and the start of the target (see figure below); Other examples include:
• inter-trial interval (ITI)
• inter-stimulus-interval (ISI)
• cue-target-interval (CTI)
period (or phase)
is used to refer to a temporal range in a more generic/abstract sense. For example, foreperiod may refer to the duration between the beginning of a trial and the onset of a stimulus.
onset_asynchrony
describes the elapsed time between the start of one entity and the start of another one (e.g., stimulus onset asynchrony; SOA)
delay
could refer to the unexpected addition of a duration (e.g., the takeoff was delayed); in general should be avoided.
latency
expresses the idea of a duration for an event that could occur right away but might for some reason take more or less time. “An input to a system produces some response which appears with a latency”; in general should be avoided.

As Martin Kleppman says in his book Designing Data Intensive Applications:

Latency is the duration that a request is waiting to be handled - during which it is latent, awaiting service. Used for diagnostic purposes ex: Latency spikes. Response time is the time between a client sending a request and receiving a response. It is the sum of round trip latency and service time. It is used to describe the performance of applications.

## Examples

• stimulus_onset refers to the duration between trial start and appearance of the stimulus;
• stimulus_duration is the duration between the appearance and the disappearance of the stimulus;
• response_time typically represents the duration between the onset of a stimulus and the completion of the response to that stimulus.
• response_onset refers to the duration between trial start (not stimulus onset) and the start of the response;
• response_offset refers to the duration between trial start (not stimulus onset) and the moment the response was completed;
• response_duration refers to the difference between response_offset and response_onset and indicates how long it took to enter the response.

In general, in data tables, we should refer to stimulus onset times relative to the beginning of the trial (time reference of the trial) and specify their duration (i.e., onset and duration, rather than onset and offset or start_datetime and end_datetime).

If there’s a need for additional time measurements, which are not part of the task parameters, these can be computed by the analyst rather than be precomputed and present in the shared data.