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Thread: Time stamp stimuli (case 8838)

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  1. #1
    Join Date
    Jul 2013

    Time stamp stimuli (case 8838)

    I am preparing a dual-task paradigm in which participants will perform some type of behavior while being video recorded and perform and button-press task in DirectRT. The video recording will be time-stamped using the computer's clock. I would like to know how to obtain the same time stamping for when stimuli are presented in DirectRT using the same clock.

    Is there a way to have DirectRT record when stimuli were presented using the computer's clock?

    I would appreciate any help anyone can provide. Thanks!

  2. #2
    Join Date
    Feb 2013
    The log files in the Data folders created by DirectRT may contain the information you need. They record the time that a session began in the time column and the started@ column keeps track of how many milliseconds passed between the start of the first trial and the current trial. By adding the strated@ value for the trial you are interested in to the value of the time column, you should be able to create the time stamp for when that trial began.
    Jason Reed
    Empirisoft Software Support Specialist

  3. #3
    Join Date
    Jul 2013
    Hi Jason,

    Unfortunately, the "Time" variable in the log Excel data file does not give accurate enough timing for when the session started. It gives hours and minutes, but not seconds or milliseconds.

    Is there a way to obtain more accurate information on when the experiment started in DirectRT syncing with the computer clock? I know this information is available in MediaLab, but the "Time" variable is not quite as accurate in DirectRT.


  4. #4
    Join Date
    Nov 2005
    We had a system a few years ago that was set up like this:

    Computer (DirectRT) --serial port--> Black Box ----> Video Recorder
    Video Camera--------------------------|

    When a new screen or video or stimulus was presented on screen, DirectRT sent a trigger command out the serial port.

    Our black box received video from the camera, overlaid timing data & trigger information from DirectRT, then output a composite video signal which contained the original content and the timing data.

    Then, using a video recorder or a computer with a video capture card, everything could be lined back up again.

    This was built years before in-computer video capture was very stable under Windows.

    I wonder if it'd be useful in this situation?


  5. #5
    Join Date
    Jul 2013
    Hi JEC,

    This "black box" sounds like it might work for our purposes. Could you provide more information on the box?

    1. Commercial built or lab constructed?

    2. What are the capabilities of the box?

    3. Did the box send some signal to the video feed or were the video and DirectRT signals combined somehow using the box?

    I'd appreciate any further information you could provide. Thanks!

  6. #6
    Join Date
    Nov 2005
    The system is something we've designed in-house.

    The black box has two inputs - composite video and an RS232 (serial port) and one output (composite video).

    Incoming video then can have arbitrary text overlaid on top of the image in nearly any location.

    MediaLab / DirectRT can then send commands through the serial port which display text on different areas of the screen. For example, you might want to include the date, the subject name, or something similar.

    Further, the system includes an on-screen timer which matches up with video's timing resolution of 30 frames per second. This timer can be started, stopped and cleared through the serial port. Thus, the computer can send a 'timer go' command when a new stimulus is displayed on screen, and then the on-screen overlay clock will increment on its own until stopped.

    Does that help?

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