Have you ever seen the one about two words being repeated and how your mind adjust somehow and just sees one word. Now where did I see that?

I know it was a psychology class I took, it was something like

Have you ever
been to Paris in the
the spring

or something like that, I just don't remember the words they used!! If any of you guys can remember or know that one, would you please remind me. Now I'll be racking my poor brain all night!

Willie