eprime timing issues and wierd time log

[sally]

Dear all,
 
Recently I find there is a strange thing about eprime. I am engaged in an 
fMRI experiment. So there is a strict timing demand and I wrote several 
lines of codes to make it possible in the scanner that subjects use two 
keys to move the cursor in the screen to do rating from 1-9. 
The very obvious problem is that when I run the codes, some presentation 
before the 1-9 ratings has got something like time ceiling. the rating time 
is always fixed as I assigned in the codes,but sometimes, the fixation time 
after the rating is shorten to 0, or sometimes the picture showing time 
after the fixation also flash more quickly than I expected while another 
fixation after the picture is still shown as I hoped. It's  totally out of 
my mind. pictures didn't show up for the time I demand in the duration menu.
I think this may have something to do wt my rating part. So I'd better to 
write out how I realize this part:
 
Another guy give me this idea to make the rating 1-9 shown for 0s and 
afterwards every time I press the button I set up in the rating slide to 
left or right move the cursor, the eprime would catch the response and 
check which btton is pressed and make a decision whether the cursor move 
left or right and how long it would move. then after the axis is 
determined, I would draw the rating slide. and I have a cycle to control 
the time by datediff functon to check the start and the end of the cycle is 
about 5s apart.
 
I hope I make myself clear.
 
Any idea would be appreciated and hope someone can help me.
 
My best,
 
Sally

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