Laptop screen refresh rate - unusual question

Hi, I wonder if anyone could offer some advice? I'm planning to run some experiments on my new Toshiba L300 laptop. I'm doing my final year at uni and investigating subliminal perception. (I'm actually 51 years old - mid life crisis - missus wouldn't let me have a Harley so I'm doing a degree instead).

What I need to do is expose images on the screen very quickly. I gather that laptop refresh rates are about 17 milliseconds, so I know I can't go faster than that. What would happen if I set my software to expose for say, 25 milliseconds? Would that result in multiples of 17 ms frames, resulting in 2 x 17ms = 34ms? or can I get precise timings (within reason)?

Any advice on this would be really useful. I know at Uni they use an old Trinitron based CRT monitor for fast exposures. I don't need that but I do need to know how fast I'm actually exposing the image for.

Thanks Adge

 

welcome to nbr.
I think that what you are trying to achieve will work. I know that when making a few video projects for school, I inserted a bunch of pictures into the video, to add subliminal messages. This was for an arts class, so it was fine.
I made each picture 1 frame, so at 30 frames per second, the image appeared for 1/30th of a second. With Adobe Premier that was the fastest I could go. When playing the video on a laptop computer, the images were still present, but when its playing at 1/30th of a second, i can barely catch any of the images I put in.
Most CRT screens can do 85-120Hz so they have the advnatage for faster refresh times than most lcd's.

Good luck with your project, plus its much safer to play with computers than motorcycles. Your wife is doing something good for you

K-TRON

 

K-T brings a point to the table. What software will this be done on as I suspect it could be the bottleneck not the monitor. Do they have special software on those CRTs Uni uses?

If I understand on the psychophysics side 16 fps reaches the flicker fusion threshold for most. But this would be different because it would I believe not be the sequential similar but an abrupt variation so at 16 fps might not cut it. Would 32 be enough? Of course more is better.

What can your software do? Also you may be restricted to multiples of the refresh rate. If 17ms then 25ms would not be possible? 34ms yes. Sounds worth pursuing to me. Good luck.

 

most if not all laptop screens refresh at 60Hz, which is 16.666666 mS ... so yeah, 17mS is about the fastest you could go. On LCD monitors.

CRTs vary from 50Hz up to like 140 Hz.

so I would think that you would most likely get multiples of 17mS frames .. unless it does one frame and cut the next one in half (not likely). As far as I know, the video card loads frames in the video memory first and then display those ... or in other words it loads the second frame in say 0.1mS and then wait the next almost 17mS to display it, in which case you will get 2 full frames regardless of the initial software.

if you think about it, most video cards support external (say CRT) monitors that can refresh faster than LCDs .. so the video cards surely support higher refresh rates too.

 

Thanks for the replies. The software I will be using is specially designed for producing subliminal experiments (E-Prime). I'm not sure how the images are displayed by the software, I suppose just by switching a jpeg image on and off for the desired time interval and you've confirmed what I suspected - multiples of just under 17ms exposures which is perfectly fine. Just in case you're interested - I'll be showing a quick exposure of a fearful face about 20-50milliseconds immediately followed by a neutral face for about 100-120milliseconds. The first face cannot be detected at all but is registered by the unconscious mind. So, the tales about "buy Coca Cola" subliminal cuts in 1950's movie theaters (that was a hoax) actually can work. It may be doable with Flash for website banners!

Thanks again - Alan