sample block duration and StimulusDuration

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jslater
Posts: 1
Joined: 26 Apr 2017, 16:28

sample block duration and StimulusDuration

Post by jslater » 26 Apr 2017, 16:44

I have been using BCI2000 to present stimuli and today encountered these errors after altering the stimulus matrix:
"Due to a sample block duration of 200ms, the actual value of StimulusDuration for stimulus 1 will be 400ms rather than 600ms."
"Due to a sample block duration of 200ms, the actual value of StimulusDuration for stimulus 8 will be 1000ms rather than 1200ms."

I have encountered this before and thought the error made sense when the stimulusduration was not a multiple of the sample block duration, but in this case I don't understand why there's a problem with durations of 600ms and 1200ms, but not for 200, 400, 800, 1000 or 1600ms, given the sample block duration is 200ms.

I am also unclear about how the StimulusDuration parameter influences this, so maybe that's the missing piece! I did try several different values but was not able to remedy the problem.

Thanks!

mellinger
Posts: 1035
Joined: 12 Feb 2003, 11:06

Re: sample block duration and StimulusDuration

Post by mellinger » 23 Oct 2018, 12:00

I cannot reproduce your observations with my current version of BCI2000. If your SampleBlockSize fails to be exactly 200ms long, there might be rounding issues, though.

-Jürgen

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