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? <br><br>Thanks, <br><br>Justine VanDyke<br>Postdoctoral Research Fellow<br>University of South Carolina<br><br>On Friday, 10 September 2010 09:46:03 UTC-4, David McFarlane wrote:<blockquote class="gmail_quote" style="margin: 0;margin-left: 0.8ex;border-left: 1px #ccc solid;padding-left: 1ex;">When you look at the Logging tab on the properties page of any <br>stimulus object, you will find a host of items available for <br>logging. Most of these are time audit data. But what do all these <br>items mean, and what are they good for? Chapter 3 of the E-Prime <br>User's Guide discusses time auditing to some degree, and the timing <br>diagram at Appendix E provides one way to see the relationships <br>between these items. As an alternative, here I try to set out, in <br>order, a brief description of these items.<p>First let us distinguish between timing control *settings* and time <br>audit *measures*. The following items do not reflect any results <br>formed during the course of a stimulus but simply log the settings <br>provided by the user (e.g., you). You may choose to have any of <br>these logged just to keep a record of settings active during the experiment:<br>- Duration: To reiterate, this does *not* show the actual duration of<br> the stimulus, only the setting as provided by the user.<br>- PreRelease: Affects the TargetOffsetTime (see below).<br>- TimingMode: Event, Cumulative, or Custom, as set by the user (see<br> the online E-Basic Help).<br>- CustomOffsetTime: In Custom timing mode, overrides the<br> TargetOnsetTime (see the online E-Basic Help).<br>- CustomOnsetTime: In Custom timing mode, overrides the<br> TargetOffsetTime (see the online E-Basic Help).</p><p>Now, the raw time audit measures, listed in the order in which events <br>occur during the execution of a stimulus object. These are all time <br>stamps in milliseconds from the start of the current program run:<br>- StartTime: Time at which E-Prime started executing the stimulus<br> object.<br>- TargetOnsetTime: Scheduled time at which presentation of stimulus was<br> to begin; set automatically from GetNextTargetOnsetTime (see online<br> E-Basic Help).<br>- OnsetTime: Time when E-Prime actually submitted the stimulus data for<br> presentation (e.g., proceeded to copy data to display memory or load<br> sound buffer). This may not coincide with when the stimulus actually<br> got presented, e.g., if data are submitted in the middle of a display<br> refresh cycle then they may not get presented until the next refresh.<br>- ActionTime: According to the online E-Basic Help, time at which<br> E-Prime completed the "critical action" of the stimulus. The<br> documentation remains somewhat vague about this -- perhaps "critical<br> action" means copying data to display memory, or loading a sound or<br> video buffer. In my tests, ActionTime never lags more than 1 ms<br> behind OnsetTime, so it serves practically the same purpose as<br> OnsetTime.<br>- TargetOffsetTime: Scheduled time at which offset actions (e.g.,<br> clean-up, ClearAfter, StopAfter) of stimulus object were to begin,<br> e.g., OnsetTime + Duration - PreRelease (Event timing mode), or<br> TargetOnsetTime + Duration - PreRelease (Cumulative timing mode).<br>- OffsetTime: Time when E-Prime actually began the offset actions of<br> the object. Actions may not take practical effect until next<br> vertical blank, or until presentation of next stimulus.<br>- FinishTime: Time when E-Prime exited from execution of the<br> stimulus object and proceeded to execute the next section of the<br> program (e.g., next stimulus object or inline code). Note that<br> *execution* of a stimulus *object* may end before *presentation* of<br> the *stimulus* ends; this is the point of PreRelease (as well as<br> happening as a matter of course with some stimuli such as some<br> sounds).</p><p>Finally, a few composite time audit measures derived from the raw <br>measures above and provided for convenience:<br>- OnsetDelay = OnsetTime - TargetOnsetTime<br>- ActionDelay = ActionTime - OnsetTime<br>- OffsetDelay = OffsetTime - TargetOffsetTime<br>- DurationError = OffsetTime + PreRelease - OnsetTime - Duration</p><p>Note:<br>- Time audit measures include the ActionTime that follows upon<br> OnsetTime, but no corresponding item to follow upon OffsetTime.<br>- No time audit item for time stamp of vertical blank, although many<br> stimuli do not take full effect until just after a vertical blank.</p><p>-- David McFarlane, Professional Faultfinder</p><p></p><p></p><p></p><p></p><p></p><p></p></blockquote>
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