OnsetDelay and resolution problem?

[Vaaal]

Hi,
I am trying to design an experiment with precise timing measure. In order 
to make my problem clear, I have to give some details about my experiment.

The order of the slide is
CROSS - FP - LANDC - BLANK.
The "timing important" frames, however, are only the last three. 

CROSS, FP and LANDC have "PreRelease" on (same as duration), the forth one 
doesn't have any prerelease. This is because the forth frame is a response 
frame, so the prerelease would be useless.

The CROSS slide lasts 1000 milliseconds and has prerelease. FP duration, 
however, changes everytime (reading from an attribute "Duration" in the 
trialList).
LANDC lasts 200 milliseconds. LANDC is a slide with an image object, and 
the image is in a directory specified by another attribute ("Image") in 
trialList.
BLANK wait for the subject response.

All the subject but LANDC are blank slides.

The refreshAlignment is 50%.

I am not interested in the timing of the CROSS slide.

When I test my experiment on my office computer, the delay of FP and BLANK 
is around 0. The delay of LANDC is more variable (from -8 to 8, usually). 
The resolution in this computer (LCD) is 1920x1080 at 60Hz. I can accept a 
delay of max  +-((1000/60))/2 ms. This means that for a refresh rate of 
60hz, it is fine for me if the slide appears +- 8 ms before/after it is 
supposed to appear. Ifigured that FP and BLANK have a delay of 0 because 
the duration of their previous frame is a multiple of 16.66 ms. This seems 
to be the case: the CROSS slide duration, as said before, is 1000 (and 
16.66*60 is 999.6). The duration of LANDC is 200 (16.66*12=199.92). 
However, LANDC doesn't have a delay of 0 because its previous frame, FP, 
doesn't have a multiple of the refresh rate (and I will not change that: 
the duration of FP changes constantly, according to the Duration attribute).

The onsetDelay of 0 for the two frames is a lucky coincidence, and it is 
not required to be zero. As said before, it could be anything between 
+-(1000/refrashRate)/2.

Now, MY PROBLEM IS that when I try the experiment on ANOTHER MACHINE the 
onsetDelay behave in a problematic way.

When the resolution is 1600x1200 70Hz, I have almost perfect result when 
the refresh rate is 75Hz or lower. If the refresh rate is 85 or 100Hz, I 
have a OnsetDaly of approximately 11-12ms for all of the three slides (FP, 
LANDC and BLANK). Why this happens???

I could just stick with the 75Hz or lower rate, you could say. In my 
experiment, however, I highly prefer to use an high resolution. I tried a 
lot of different combination of  resolution/refresh rate, and all the 
higher one lead to a dramatic (10/15 ms) increase of the onsetDelay for all 
the three slides.
In particular I tried=
2048x1539, 75Hz and 60Hz
1920x1440, 85Hz, 75Hz, 70Hz and 60Hz.
1920x1200 70Hz and 60Hz.
1920x1080 70Hz


I also tried with 1600x900. In this case, the results were good (around 
zero for CROSS and BLANK, within a reasonable range for LANC).

So, it seems that, REGARDLESS of the refresh rate, at high resolution the 
onsetDelay increase.

Does anyone have any idea why this happens? *Does anyone have any 
suggestion about HOW COULD I USE HIGH RESOLUTION WITHOUT ONSET DELAY?*

Just for your information: the second monitor is a CRT Sony GDM-F520 
(specs= http://www.docs.sony.com/release/specs/GDMF520_sp.pdf ). As you can 
notice, the recommended resolutions are 1920x1440 85Hz, 1800x1440 85Hz and 
1600x1200 85Hz. For some reason, I cannot set the resolution to be 
1800x1440. 
Anyway, as you can see I tried a lot of combination without success. I 
really need my resolution to be high (>= 1920x1200). The refresh rate is 
not so important, but since it is a CRT monitor I would prefer it to be 
higher than 72Hz. 

I really don't know what to do :(
Any help is highly appreciated.
Best Regards,
Valerio

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