Mastering E-Prime: Meaning of all time audit measures.
David McFarlane
mcfarla9 at msu.edu
Fri Feb 22 17:51:02 UTC 2013
Slight correction -- logging of OnsetToOnsetTimes works for both
"Standard" (i.e., base) and Professional editions of EP2.0.10.x.
-- David McFarlane
At 2/22/2013 12:42 PM Friday, David McFarlane wrote:
>Sylvain,
>
>At 2/22/2013 06:36 AM Friday, Sylvain wrote:
>>Hi David,
>>
>>I have a question regarding to pre-release and timing.
>>
>>I did a little experiment trying to get the timestamp of the onset
>>of stim, and the offset or it.
>
>Wonderful, everyone should do these sorts of explorations (that's
>how I figured out all this stuff).
>
>
>>It's simple basically i have :
>>
>>- Inline1: I collect t1 = Clock.ReadMillisec
>>- Then an ImageDiplay for 200 ms with a pre-realase equal to the
>>duration of it. I log the onset of ImageDiplay and the offset of it;
>>- Inline 2: I collect t2 = Clock.ReadMillisec
>>
>>Doing that, basically I get t2-t1 almost equal to 0 modulo some
>>refresh rates.
>>I also get ImageDiplay.OnsetTime = ImageDiplay.OffsetTime.
>
>As you should. You might find OffsetTime slightly behind OnsetTime;
>and under these conditions (PreRelease = Duration), you should find
>that TargetOffsetTime = TargetOnsetTime without exception.
>
>
>>1) There's something there that I don't really understand, which
>>timestamp should I really consider, ImageDiplay.OnsetTime or
>>ImageDiplay.OffsetTime?
>
>That depends entirely on what you wish to do with that timestamp.
>
>
>>2) If I understood pre-realase affect offset time, so does that mean that:
>>ImageDiplay.Duration = (ImageDiplay.OffsetTime
>>- ImageDiplay.OnsetTime) + pre-realase
>
>Not quite -- E-Prime can control only *Target* offset (& onset)
>times, not actual times. Actual offset (& onset) times are subject
>to the limitations of the stimulus presentation hardware. Also, I
>would not write the relationship that way -- that makes it sound
>like Duration derives from the other quantities, which is wrong. As
>I described earlier, Duration remains whatever you asked it to be,
>so should appear only on the right side of the equals sign as it is
>used to determine other quantities. Thus, repeating what I wrote in
>my earlier description of TargetOffsetTime, in the case of Event timing mode,
>
> ImageDisplay.TargetOffsetTime = ImageDisplay.OnsetTime +
> ImageDisplay.Duration - ImageDisplay.PreRelease
>
>Note that, in the case PreRelease = Duration (the new default
>setting since EP2.0.10.x), we get simply
>
> ImageDisplay.TargetOffsetTime = ImageDisplay.OnsetTime
>
>which fits your observations. If instead we set PreRelease to 0, we find
>
> ImageDisplay.TargetOffsetTime = ImageDisplay.OnsetTime +
> ImageDisplay.Duration
>
>which perhaps is what you expected (and was the default for Event
>timing mode prior to EP2.0.10.x).
>
>And just to drive the point further, OffsetTime does *not* indicate
>the time at which *presentation* of a stimulus ends. Rather, (for
>most practical purposes) it indicates when *execution* of the
>stimulus Run method ends (strictly speaking, this describes
>FinishTime, see my earlier description for the fine distinction
>between OffsetTime and FinishTime).
>
>Furthermore, even with PreRelease set to 0, neither Duration nor
>(OffsetTime - OnsetTime) necessarily indicate the actual duration of
>the stimulus. In particular, a visual stimulus does not disappear
>at its OffsetTime (ignoring Clear After, which has been deprecated),
>but remains visible until replaced by another visual stimulus, so
>actual presentation duration is
>
> Stim2.OnsetTime - Stim1.OnsetTime
>
>and EP2.0.10.x Pro can now log those values for you
>(http://www.pstnet.com/support/kb.asp?TopicID=718 )!
>
>
>>3) The fact that Inline2 is executed at the same time as Inline1 is
>>particulary disturbing for me. Does that mean than Inline placed
>>after an object could be executed while this object is still on screen?
>
>Yes, and that is exactly what we want it to do in many, many cases
>(e.g., to handle multiple mouse actions while a visual stimulus
>remains on the display, or to prepare the next stimulus during the
>run of the current stimulus). If you really want your InLine to
>wait until the previous object completes its Duration, then set
>PreRelease of that object to 0.
>
>Hope that helps,
>-----
>David McFarlane
>E-Prime training
>online: http://psychology.msu.edu/Workshops_Courses/eprime.aspx
>Twitter: @EPrimeMaster (https://twitter.com/EPrimeMaster)
>
>
>>Thank you for any answer, I'm confused about this!
>>
>>Sylvain
>>
>>On Friday, September 10, 2010 3:46:03 PM UTC+2, 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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