How long does it take us to be aware of what we see?
In addition to only having a very limited sharp field of vision, our eyes are also fairly slow at registering changes in images compared to the update frequency of a modern computer screen. Research has shown that the retina needs to see a new image for about 80 ms before that image is registered in normal light conditions. This doesn’t mean that we consciously have noticed any changes—only that the eye has registered a change. The ability to register an image is also dependent on the light intensity of that image. This can be compared with a photographic camera where a short shutter speed in a badly lit environment results in a dark and blurred image, where hardly anything can be seen. However, when taking an image of something that is very well lit, e.g. a window, the shutter speed can be very short without this problem occurring. In addition to needing time to register an image, the eye also requires time for the image to disappear from the retina. This is also dependent on the light intensity. One example of this is when exposed to a very bright light such as a camera flash where the image of the flash stays on the retina long after the flashing has ended.
In addition to the eye’s light sensitivity, how fast we perceive something we are looking at also depends on what we are observing. When reading in normal light conditions, it has been observed that most people only need to see a word for between 50–60 ms in order to perceive it. However, when looking at, for instance, a picture people need to see it for more than 150 ms before being able to interpret what they are seeing.