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Forum Newbie
Group: Forum Members
Last Login: 7/25/2007 4:52:25 PM
Posts: 2,
Visits: 2
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Dear E-Prime users,
I am having a problem flickering stimuli for a SSVEP experiment.
What I want to do is this: Flash a stimulus at 10 Hz using a 60 Hz monitor.
i have "on" frames and "off" frames. Both stimuli are negative contrasts of each other. So what I want to do is to display 3 frames on and 3 frames off to have a cycle of 6 frames, achieving the desired stimulus flicker rate (60 / 6 = 10).
What happens now is that when the experiment runs, I get an ugly artifact: a horizontal line that divides the screen between an on and off frames. This line changes position on the screen (sometimes it is on top and other times it is on the bottom)
Here is how I am displaying the images:
Each stimulus is a ImageDisplay type. I have the Duration set to 17 ms (1/60 * 1000). The timing mode is cumulative, and OnsetSync is set to 1, OffsetSync is set to 0. Playing with the Onset and Offset sync properties effects the artifact, but doesn't remove it. Their order of diaply is controlled by a
I am using a dual display system - one display is LCD, the other is CRT. Both are set to 60 Hz. The artifact is not present in the LCD display.
Thanks in advance,
Andre
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Forum Newbie
Group: Forum Members
Last Login: 7/25/2007 4:52:25 PM
Posts: 2,
Visits: 2
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| I fixed the problem - It turned out that the dual display setting was causing the artifact. Plugging in the crt directly to the video card solved it. -Andre
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