uigetvarname

  Part of the NewStim package
  NAME = UIGETVARNAME(PROMPT, DEFAULT)

   Prompts the user for a variable name until they cancel the window or enter
   a valid variable name.  PROMPT should be a string prompting the user, and
   DEFAULT is the default variable name (or use '' for blank).  If the user
   clicks cancel, then the empty string is returned.