Mastering E-Prime: Meaning of all time audit measures.

[David McFarlane]

When you look at the Logging tab on the properties page of any 
stimulus object, you will find a host of items available for 
logging.  Most of these are time audit data.  But what do all these 
items mean, and what are they good for?  Chapter 3 of the E-Prime 
User's Guide discusses time auditing to some degree, and the timing 
diagram at Appendix E provides one way to see the relationships 
between these items.  As an alternative, here I try to set out, in 
order, a brief description of these items.

First let us distinguish between timing control *settings* and time 
audit *measures*.  The following items do not reflect any results 
formed during the course of a stimulus but simply log the settings 
provided by the user (e.g., you).  You may choose to have any of 
these logged just to keep a record of settings active during the experiment:
- Duration:  To reiterate, this does *not* show the actual duration of
   the stimulus, only the setting as provided by the user.
- PreRelease:  Affects the TargetOffsetTime (see below).
- TimingMode:   Event, Cumulative, or Custom, as set by the user (see
   the online E-Basic Help).
- CustomOffsetTime:  In Custom timing mode, overrides the
   TargetOnsetTime (see the online E-Basic Help).
- CustomOnsetTime:  In Custom timing mode, overrides the
   TargetOffsetTime (see the online E-Basic Help).

Now, the raw time audit measures, listed in the order in which events 
occur during the execution of a stimulus object.  These are all time 
stamps in milliseconds from the start of the current program run:
- StartTime:  Time at which E-Prime started executing the stimulus
   object.
- TargetOnsetTime:  Scheduled time at which presentation of stimulus was
   to begin; set automatically from GetNextTargetOnsetTime (see online
   E-Basic Help).
- OnsetTime:  Time when E-Prime actually submitted the stimulus data for
   presentation (e.g., proceeded to copy data to display memory or load
   sound buffer).  This may not coincide with when the stimulus actually
   got presented, e.g., if data are submitted in the middle of a display
   refresh cycle then they may not get presented until the next refresh.
- ActionTime:  According to the online E-Basic Help, time at which
   E-Prime completed the "critical action" of the stimulus.  The
   documentation remains somewhat vague about this -- perhaps "critical
   action" means copying data to display memory, or loading a sound or
   video buffer.  In my tests, ActionTime never lags more than 1 ms
   behind OnsetTime, so it serves practically the same purpose as
   OnsetTime.
- TargetOffsetTime:  Scheduled time at which offset actions (e.g.,
   clean-up, ClearAfter, StopAfter) of stimulus object were to begin,
   e.g., OnsetTime + Duration - PreRelease (Event timing mode), or
   TargetOnsetTime + Duration - PreRelease (Cumulative timing mode).
- OffsetTime:  Time when E-Prime actually began the offset actions of
   the object.  Actions may not take practical effect until next
   vertical blank, or until presentation of next stimulus.
- FinishTime:  Time when E-Prime exited from execution of the
   stimulus object and proceeded to execute the next section of the
   program (e.g., next stimulus object or inline code).  Note that
   *execution* of a stimulus *object* may end before *presentation* of
   the *stimulus* ends; this is the point of PreRelease (as well as
   happening as a matter of course with some stimuli such as some
   sounds).

Finally, a few composite time audit measures derived from the raw 
measures above and provided for convenience:
- OnsetDelay = OnsetTime - TargetOnsetTime
- ActionDelay = ActionTime - OnsetTime
- OffsetDelay = OffsetTime - TargetOffsetTime
- DurationError = OffsetTime + PreRelease - OnsetTime - Duration

Note:
- Time audit measures include the ActionTime that follows upon
   OnsetTime, but no corresponding item to follow upon OffsetTime.
- No time audit item for time stamp of vertical blank, although many
   stimuli do not take full effect until just after a vertical blank.

-- David McFarlane, Professional Faultfinder

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