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E-Prime Timing Considerations

E-Prime Timing Considerations. EGI Summer School 2005. Millisecond Precision Defined. Standard Definition : Being able to ask the system clock what time it is every millisecond. E-Prime Provides : A measured and reported timing precision standard deviation is less than half a millisecond.

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E-Prime Timing Considerations

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  1. E-Prime Timing Considerations EGI Summer School 2005

  2. Millisecond Precision Defined • Standard Definition: Being able to ask the system clock what time it is every millisecond. • E-Prime Provides: • A measured and reported timing precision standard deviation is less than half a millisecond. • Recordings are within a millisecond from the time they are available to computer hardware. Any errors should be detectable and not increase measurement variance by more than 1ms. The investigator should have a method available to identify and filter out timing data that is in error • Screen refreshes (displays of the full screen) can be tracked without misses 99.9% of the time, and misses can be detected and reported

  3. Limit Timing Errors by: • Run at Highest Priority and terminate other programs • Use prerelease on objects preceding critical objects • Synchronize with refresh cycle • Choose the correct timing mode • Logging the millisecond timestamp of all actions

  4. Determine Your Critical Timing Needs • Single stimulus event to response timing • Critical sequence of events • Critical and varying duration of an event in a sequence • Cumulative timing of a repeating sequence of events • Continuous sequences of events at a high rate with short stimulus presentation durations

  5. Prerelease To ensure unintended delays in onset time of a particular object, a PreRelease time should be set for the previous object. Every stimulus object has a PreRelease setting to allow the following object to be prepared prior to the termination of the current object. PreRelease allows one stimulus to absorb the setup time for the next stimulus, while it waits for its targeted end-time.

  6. Synchronize With Refresh Cycle All operations on a computer that involve interaction with the video device, must be synchronized to the refresh rate of the monitor. E-Prime stim objects default to synchronize their onset with the vertical blank. Users can eliminate unpredictability in event durations by making all object durations multiples of the refresh rate. For example, if the intended duration is 100 ms and the refresh rate is 60 Hz, the duration should be set for either 85 ms or 102 ms

  7. Choose the correct timing mode • Event Mode: Duration of event is fixed. This results in a delay of the onset of all subsequent events due to the error, and an accumulation of timing delay across events. • Cumulative Mode:delays in the onset of an event result in an equivalent reduction in the duration of the event, such that the cumulative timing error is minimized. • Custom Timing Mode: allows users to alter timing using E-Basic

  8. Logging the Millisecond Timestamp of all Actions • The accurate logging of timing data is the principal line of defense against the operating system or hardware putting artifacts into data • By logging stimulus timing data you can identify those errors, and when they occur you can choose to include or exclude the data from trials on which they occur in your data analysis

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