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Forum Newbie
Group: Forum Members
Last Login: 11/2/2007 2:29:27 PM
Posts: 1,
Visits: 4
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Hi!
I use a light-sensitive diode attached to the screen to measure the time of the appearance of a stimulus.
Monitor settings are 1280*1204 pixel resolution, 60Hz refresh rate and 16 bit colour depth (DELL_2001FP Monitor). The settings of the monitor device in the e-prime program are accordingly.
I wrote a very simple program, which uses the OnsetSignal command to send a trigger when a slide display with a black box shall be loaded. Now, I compare the time when the trigger appears in the EEG data to the time when the diode signal is reacting to the stimulus on the screen (the black box in the upper left corner). When I test the program repeatedly, I get a delay of about 30ms which is very constant within one run of the task (20 times the stimulus presented) as well as between repeated runs of the task.
However, when I restart the computer, I get a different delay (which is again constant within and across runs).
(I also tried to wait a couple of minutes and test again, the delay does not change then)
This is not the case, when I am not loading a picture, but when I just show alternating white and black screens.
Does anybody now what this might be due to and how I can get a constant delays across restarts of the computer?
Please find the program attached.
Thank you very much in advance,
Dorothea Hämmerer
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