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

[justine]

I am in the process of conducting my own timing tests (for an 
Eprime/NetStation experiment), and this was invaluable in trying to 
understand the time audit measures. I gather from this that there is no way 
of knowing when the stimulus was *actually* presented on the screen (given 
the refresh rate). I assume this means that my triggers in the EEG record 
could be off by whatever that screen refresh delay was. Is that correct? 

Thanks, 

Justine VanDyke
Postdoctoral Research Fellow
University of South Carolina

On Friday, 10 September 2010 09:46:03 UTC-4, David McFarlane wrote:
>
> 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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