Every computer user knows that the use of "all caps," that is, text in all capital letters, is understood to mean text that the writer wants to be read as something yelled or screamed. So if I write you an e-mail telling you to "PLEASE CALL ME ON MY CELL PHONE INSTEAD OF MY HOME PHONE," to pick a random example, you're likely to think I'm very upset. If I write the same message in lower case letters, you won't naturally draw that conclusion.

  I wonder, where did this come from? Is it just a social convention? If so, where did it originate? Alternatively -- or additionally -- does a psychological explanation exist for it? Capital letters generally are larger than lower-case letters. Do we intuitively associate expanded size with increased emotion, as if letters mirrored the dilated pupils of the fight-or-flight reaction?

  Okay, so it's kind of a random question. But does anyone know the answer?