Converting a string

I think that we did this before, but I cannot find my notes or in the archive because I am not sure what we called it. Let us say that that I have a form item (I'll leave out clutter); <input name="psFirstName"> It arrives in processing as $_POST['psFirstName'] Now, I have one of these for each form item, each with a different name. In my error script I want to say "Cannot leave First Name blank" I need to convert psFirstName to First Name. I tried preg_split, but it cuts away the capital letters. Can someone point me in the right direction again? Thanks!