Refresh rate TFT

[Michiel Spape]

Hi David & List,
Stockpiling CRTs worked for us quite well as well, but the screens are getting quite old. As a results, it might be nice if we can ascertain where exactly the problem is and what we can practically do about it (given the instance where a CRT is unavailable). 
1. As far as I know, the problem you describe used to be worse than it is these days; the sort of blurry effect one had when moving a mouse-pointer, for instance, seems to be pretty much gone. What to look for with LCD screens to get 'high performance'?
2. Am I correct in the understanding that it is not the problem that LCD pixels get bright fast, but, rather that they turn dark again slower? If so, it would, all in all, be a rare thing that one could not design an experiment around it. For instance, if I have a subliminal white prime with a duration of 16 ms, it won't turn dark after 16 ms. However, it won't turn dark on your retina either, and for this reason we usually mask stuff (say, a white pattern mask). Yet, if that would be impossible, would using inverse colours (a black prime), or some other colour scheme help? 
Anyway, these should be some simple questions for anyone with a bit more knowledge of hardware than I have - which is rather little (I like programming, but am incredibly clumsy, which never helped). Nevertheless, I think that it would be useful to have them answered on the list, as it does seem that CRT monitors, whether we like it or not, might go the way of the videotape. 
Best,
Mich

Michiel Spapé
Research Fellow
Perception & Action group
University of Nottingham
School of Psychology
www.cognitology.eu

----------------
//snip
One more note about measuring performance of LCD/TFT vs CRT.  It may 
casually seem that images appear and disappear from the display with 
high performance, however, several years ago when we measured LCD 
performance with a photodetector and oscilloscope we found that it 
took a *long* time for "off" pixels to return to baseline (some 
hundreds of ms, as I recall).  That may not matter for your studies, 
but it mattered to us at the time.  We have not done that measurement 
again, so don't know how modern LCDs perform; instead, we have just 
stockpiled our own stash of CRTs to provide for our future studies.

Regards,
-- David McFarlane, Professional Faultfinder


At 7/1/2011 05:54 AM Friday, you wrote:
>HI together,
>
>as CRTs are hard to get nowadays, we equipped our labs with tft
>screens. I wrote short and simple experiment to test the timing.
>basically, there are 4 display elements, alternating black and white
>background with nothing on it. As the refresh rate is 60 Hertz, I
>first set the duration to 50 ms (which is about 3 refresh circles).
>Prerelease is set on 20 ms.
>
>These are the results (duration, duration error, onset delay
>[according to logged data in results file])
>
>slide 1: 50, 0, 5
>slide 2: 50, 0, 0
>slide 3: 50, 0, 0
>slide 4: 50, 0, 0
>
>These are the results for a duration of 40 ms
>
>slide 1: 40, 0, 6
>slide 2: 40, 0, 10
>slide 3: 40, 0, 10
>slide 4: 40, 0, 10
>
>The first onset delay might be due to waiting for the next refresh
>circle to start. If the duration value matches the screen refresh
>rate, there seems to be no delay. If it doesn't (in this case, 40 ms),
>there is a delay that adds up to the next value that matches (50 ms).
>However, it is not clear to me how the duration arror can be 0 if
>refresh rate and duration value do not match. The screen should not be
>able to display something for 40 ms.
>
>Any ideas? Any hints for using TFTs or testing the timing of such
>screens?
>
>Thanks a lot! Cheers, Tobias

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