Hi,
We have a Nordic NeuroLab LCD Monitor at our MRI scanner, which has the following specs
Input refresh rate = 60 Hz
Image refresh rate = 120 Hz
but we're not sure what the input refresh rate and image refresh rate exactly are. Is the input refresh rate here a limiting factor -- so that, as the image refresh rate is twice the frequency, the same input frame would be displayed twice? We will be displaying flickering stimuli where the frequency of the flickering is important (SSVEP). We had run the SSVEP at 13 Hz for a monitor with a 140-Hz refresh rate and would like to doublecheck whether we will have to adopt the stimulus frequency to 60 Hz or 120 Hz.
We will also have another screen connected to the stimulus presentation PC (running on Windows 7) to monitor the study -- is the slowest refresh rate of the two screens the limiting factor or do we only have to worry about the LCD monitor that the participant will be viewing?
Thanks very much in advance for any advice!
Hi Gina,
1) It's possible that the LCD is interpolating to 120 Hz from 60 Hz, so the true refresh rate is 60 Hz. I'm not sure about this however. If you can't find out this information directly from the company, you may need a light detector to truly know (and by drawing photocell squares that change from black to white each frame using MATLAB Psychtoolbox 3 or PsychoPy or ?)
2) Only the refresh rate of the subject's LCD (and the output of the video card) should matter.
So if the refresh rate of the subject's LCD is 120 Hz and the experimenter's LCD is 60 Hz, the stimulus should be configured for 120 Hz. The stimulus won't draw properly on the experimenter's LCD, but that won't matter because the subject is receiving the proper input at 120 Hz.
3) Was the SSVEP stimulus truly at 13 Hz? Because 13 is not a divisor of 140, and I'd be interested to know how that was created.
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