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Thread: Determining cumulative time for stimuli

  1. #1
    Join Date
    Nov 2005
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    Determining cumulative time for stimuli

    [edited from support email]
    We are busy using DirectRT and have a lot of fun with it. Have I already mentioned, that I enjoy very much the way the User’s Guide is written? Well, we now want to use it for an experiment that includes the use of a MRf. Our problem is to know, at which moment exactly DirectRT presents a stimulus. We need that to be able to tell, at which stimulus the patient’s brain presents which activation. I know that the output file tells us about the time of presentation of the stimulus and the time the patient needed to respond, but it would be quite a lot of work to calculate the moment of each presentation. Is there a possibility of starting some kind of “counter” at the moment when all the introduction has been presentated and the stimuli start? That would help a lot.

  2. #2
    Join Date
    Nov 2005
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    Yes, there is a column in the log version of the data file called "started@" which will tell you the number of milliseconds passed since the beginning of the session. You could also send out a TTL signal to your other software/hardware at any point during each trial--that is also a common way of synching stimulus presentation info with psychophys data.

    Hope that helps,
    Blair

  3. #3
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    [edited from support email cont'd]

    The company NordicNeuroLab developed a so called "SyncBox" that sends triggers from a fMR to the computer that is running the stimulus programme, in our case DirectRT. Does DirectRT catch and register those triggers and do I find these also in the log-file? Or do I have to make any configurations first?

  4. #4
    Join Date
    Nov 2005
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    Yes, you could have DirectRT intercept those signals and save those data to the same file where the stim presentation data are located. Take a look at the section in the manual on receiving TTL signals for details. Let me know if you have any trouble with it.

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