> Since somewhere some computation must be done to recognize this Humans don't have a "compute intersections" ability (other than a few who have learned it lab

> Since somewhere some computation must be done to recognize this Humans don't have a "compute intersections" ability (other than a few who have learned it laboriously through algebra), we have a "see things and count them" mechanism. We aren't visually taking lines in a planar space and determining where they cross. We know what an intersection looks like, we see one, increment a counter, and find the next one. If it's less than around five, we do this all at once. Otherwise we literally count, sometimes in small groups, sometimes one at a time.