ActionScript 3.0 :: Layered Objects And Functions?

I have two movie clips on the stage: mcA and mcB, each have a function when rolled over:
 
mcA.addEventListener(MouseEvent.ROLL_OVER , aActivated);function aActivated (event:MouseEvent):void{     trace('mcA was rolled over');}mcB.addEventListener(MouseEvent.ROLL_OVER , bActivated);function bActivated (event:MouseEvent):void{     trace('mcB was rolled over');}
 
Under certain circumstances mcA may overlap mcB. When the cursor rolls over their intersecting area I would like both functions to launch, how do I do that? Currently, the problem is that only the object on the top will launch its function.