F8, F9, F10, F11, F12 no longer doing the same function

Hi. New to mac. I have a macbook pro and have had it for about a month. Ever since I purchased it F8, F9, F10, F11, F12 have all served purposes relating to volume, fastfoward, mute, etc. But now all of a sudden when I go to turn up the sound or turn it down with the F11 and F12 keys the screen clears out when F11 is hit and dashboard appears when F12 is hit. I did figure out that by clicking fn+F11 or F12 will do the volume function. My question is how did this change? I don't believe I did anything to cause this but I don't know. I did click the Expose application this past weekend but have since restarted by macbook pro. Thanks.