Hi, I'm using pd to create a flashing light on a computer screen for a psychology study. I simply need a white circle to flash twice in quick succession, or once quickly, and for the participants to tell if it's flashing once or twice.
I used a gemhead with a circle object, and experimented with using a delay to turn on and off a toggle into the gemhead. It seems the system is reliable if I keep the delays at 50 ms for everything, but unreliable if I go lower than 50 ms. I need to go as low as 17 ms delay for the circle on. Is there some kind of latency in terms of the gemhead processing the incoming signal? I can't imagine there's a great deal of computation for a single white circle. Please tell me if there's a computationally less expensive way. Thanks.

you'll have to up the frame rate to give accuracy to 50ms time slices. you need forty frames/second to avoid Nyquist foldover of 50 ms events. as that event gets quicker, the frame rate must go up accordingly. you can specify framerate from your [gemwin].

Thanks so much, Sunji. That explains the problem, and I've increased the frame rate.

However, I read somewhere that the frame rate limit for gemwin is 60 fps. Do you know is this true?
Does that mean that the quickest flash event possible is 33 ms?
I was hoping to go down to at least 20 ms per flash, if not lower (7ms according to the literature visual perception of flashes).
I appreciate your help on this.

I have never heard of the 60 frame limit. My monitors are only 60hz so I've never tried to go above. [frame 100( doesn't send an error to my console. Try and see on your system?

Will do. Thanks again.