When I run SSVEP test in which a led light flickers at 30 HZ. The flickering is visible. When I try to emulate this rate by using 120 hz monitor to show a 60 fps film in which a white circle is appears and disappears on consecutive frames, I can see the flicker. How does this coherent with the principle of persistence of vision, and film projectors that used to project the image only for 1/58 of the second and then use another 1/58 to rotate the film. Why is it that in the case of cinema we experienced the film smoothly and in the emulation we see the flicker?
Thanks for your help,
miri
ssvep versus film flickering
Re: ssvep versus film flickering
Hello miri,
human eye is capable of perceiving a flickering at 30Hz. At 60Hz showing a flickering circle which is white on every other frame will result in a flickering at 30Hz (it does not matter that you are using a 120Hz monitor, as long as the movie is indeed played at 60Hz).
As far as I know in theaters movies are shot (and shown) at 24Hz but every frame is lit three times, so the actual refresh frequency is at 72Hz. However this might not be applicable for all projectors.
Concerning the persistence of vision, I would say (based solely on my own experience) that the important factor is the contrast. In a movie any two consecutive frames are usually very similar, thus the eye will not perceive the change. A circle which changes from black to white, and thus from minimal to maximal contrast, will be seen as flickering.
Hope this helps
Jozef
human eye is capable of perceiving a flickering at 30Hz. At 60Hz showing a flickering circle which is white on every other frame will result in a flickering at 30Hz (it does not matter that you are using a 120Hz monitor, as long as the movie is indeed played at 60Hz).
As far as I know in theaters movies are shot (and shown) at 24Hz but every frame is lit three times, so the actual refresh frequency is at 72Hz. However this might not be applicable for all projectors.
Concerning the persistence of vision, I would say (based solely on my own experience) that the important factor is the contrast. In a movie any two consecutive frames are usually very similar, thus the eye will not perceive the change. A circle which changes from black to white, and thus from minimal to maximal contrast, will be seen as flickering.
Hope this helps
Jozef