The Eyes have it, Science Ref.

["Lex Systems Inc." <lex@THE.LINK.CA>]

I have an unusual question to help with.  Has anyone
ever come across the shortest interval necessary for the
human eye to register the appearance of an image?

For example, we know that you can look through the lens
of a camera and see an image flash if you release the
shutter on 1/500 of a second.  OK, so what is the highest
speed you could set and still realize that an image had
briefly flashed into view?

This is for my brother, who is a biologist.

This sort of quesion is sometimes better to get from someones
memory than a reference book.

TIA

Jim Bruce