How do I make Mountain Lion read iMessage texts as they come in? On my MacBook Air in Lion with the iMessages beta I was able to set up iMessage to read all incoming messages automatically with text to speech.

I can't find how to turn that on with Mountain Lion.

I see how I can make it announce or I can select text to have it read out loud but I had it just automatically reading incoming messages out loud with text to speech before.
iMessage->Preferences->Alerts check 'Speak an announcement'