controller code for access to params in radio button column

I am new to Rails, and I thought I understood params, but I'm a little
fuzzy on what goes into the controller to access a third value for a
radio button. In my migration I defined the column as a string with a
default value of nil.
The column itself is actually a question(no question mark appears in the
column though)with three choices in the radio button form: yes, no, and
Everything works fine, but I don't know how to get undecided to display
in the table instead of yes. I'm sure this is a common scenario, but I
can't seem to get the controller stuff right, HELP! This is what I
currently have in my controller:

def Undecided
  #GET /achvrs/Radio_ButtonValues
  radio_button_results = params[:undecided_id].split
  ["Yes" "No" "Undecided"]
  PUTS params[:id]

Thanks in advance, --Stacey