question about seeing motion pictures for anyone who understands the human eye?

[JustinH3223]

I believe it's common knowledge that movies in a movie theatre are projected at 24 frames per second (basically 24 distinct images per second). But what is not common knowledge is that each image is projected twice with a blank spot in between.The way it works is there is a circular shutter between the light and the film this shutter spins once for each frame. The shutter has two open and two closed spots evenly spaced. As it spins, the film advances while the shutter is closed. Then the shutter opens and the frame is projected. Then the shutter is closed. Then the shutter opens and the frame is projected again. Then the shutter closes and the film advances and the process is repeated.My question is why don't we perceive the blank spots, or at least a flicker? And what is the minimum frame rate to perceive motion rather than a series of still pictures.I'm not sure physics is the right category for this, but I couldn't think of a better one - other than maybe biology.