Dear Nicola,Almost all (in fact I do not know of any exception) commercial projectors have a built-in internal refresh rate of 60 Hz, which is the rate at which frames are really projected, independently of the input frame rate. This frequency is historically that of most old CRT displays, which used to synchronize to the power frequency of 60 Hz (most of them where manufactured in USA)
When connected to a graphic card running at a different rate, they adapt themselves by subsampling or oversampling the frames sent by the graphic card. If you ask for 120 Hz refresh rate, they will display every second frame.
In all cases the latency between the PC frame and the projector frame will be unstable, specially when the asked rate is not a multiple of 60 Hz (selecting 80 or 100 Hz is a very bad idea)
This also means that you cannot display subliminal images shorter than 16 mS (1/60 sec), if you try for example running at 120 Hz, this single short frame will be either missed or displayed on a twice longer projector frame.
A few faster (and expensive) projectors exist on the market, the faster rate being often at the expense of resolution, and sometime only black & white. You can find them over Internet.
I hope this helps
Best,
Dear all,
we plan to run some MEG studies with high-(temporal) frequency visual stimulation. We have a Windows Xp PC, equipped with a high-quality graphic card and connected both to a CRT computer and to a Panasonic projector (Panasonic PT-D7700). The projector specifics allow stimulation up to a temporal resolution of 120 Hz. However, (after setting the primary CRT monitor at 100 Hz) when we measure with the oscilloscope this parameter, it cannot reach 100 Hz, but it reveals a 60 Hz frequency rate. After contacting Panasonic we did not receive any useful feedback. Thus, I am asking if anyone faced a similar problem and consequently developed some knowledge on how to deal with it.
Nicola
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Nicola Molinaro, Phd
Staff Scientist