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Forum Member
 
Group: Forum Members
Last Login: 7/30/2007 6:06:51 PM
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| Hello, When reading about "Event Mode Timing" (pp.90 of User's Guide) it says : In Event mode, delays in the onset of an event will not affect the specified duration of the event. This results in a delay of the onset of all subsequent events due to the error, and an accumulation of timing delay across events. For example, assume you wanted to present 5 stimuli in sequence for 100 ms each. If there was a timing error of 20ms before the second stimulus, and a 30 ms delay before the fourth event, the duration of all five events would be 100ms but the relative start times would be at 0, 120, 220, 350 and 450ms. This does not make sense to me. If event1 is displayed at 0ms, and event2 is displayed at 120ms, this means event1 was displayed for 120ms, not 100. Its duration is therefore 120ms. Also, if event3 is displayed at 220, and event4 is displayed at 350, then event 3 was displayed for 130ms (350-220 = 130). Delays in onset therefore increase the duration of the stimuli, contrary to what the manual says.
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Forum MVP
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Last Login: 2 days ago @ 8:55:28 AM
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| For easy math, picture having objects A B C all have a duration of 1000. Object A starts at time 5487. In the ideal case, object B would start at time 6487. However, object B syncs with the vertical blank which falls at time 6492. Object B then onset time would be 6492, its OnsetDelay would be 5. In the ideal case, object C was to start at 7487. However, since object B started "later", the object C is scheduled to start at 7492. It again may not start at 7492 because of sync with vertical blank. In short, one could view event timing to mean that you want emphasis on the duration of the object where in cumulative mode the emphasis is on the exact start time of the object even if it means cutting its intended duration short. -Brandon
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Forum Member
Group: Forum Members
Last Login: 7/30/2007 6:06:51 PM
Posts: 25,
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| I see. It is clear now. However, meaning of "duration" seems to change from line to line. Sometime duration means "intended duration", sometimes it means "actual duration" and sometime it means "Onset-Onset interval". This is very confusing. It took me a while to figure out that "actual duration" is not the same thing as "Onset-Onset interval".
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