Aliens dont see they are like sharks they feel electrical impulses in the air (as far as i know any way) hence why they can attack the predators even though they are invisible
also, in AvP (the game) when playing as the xeno you see a aura around your prey belived to be the electical field around human/predator
If anyone has watched some of the bonus features on the Alien Quadrilogy, you may remember as i do, a feature in which a collector discussed the various versions of the alien's in the film as he had 4 film used props behind him. He said that the one from the first film is his favorite because you can make out what appears to be eyes behind the translucent dome head.
the aliens don't really have eyes, but they see through pheromones, the same as the predator visor, if you remember Predator 2, they said that in there, not the aliens part though
Aliens don't need no stinkin Eyes. they're better without them.
btw, Director Ridly Scot said that he wanted the ALIEN to not have eyes. so as to make it even more frightening. so you can't tell if it's aware that your there. its that that makes it even more mystyriouse. you can't tell if it sees you there. so it may attack you or it may not.