I have heard all my life that they can see them and I have a firend that I use to work with that swears one of his cats sees something in his house that scares the daylights out of him and makes the cats fur stand streight up. It is a place by his satircase that is where the cat sits and watches for hours, he growls with his fur standing up then bolts in the oppsite direction... and this happens a lot. When the cat wants to go upstairs, he said he will walk through 2 rooms to get to the staircase, rather than use the hall where he "sees" this whatever it is.

I think they are on a differnt consious (spelling?) level than we are, hearing and seeing so I personally, think they do see things we can't.