Listed below are the steps required for enabling text to speech feature on Mac OS X Lion. Mac users can opt for text to speech using the options provided as part of Mac System Preferences.
Click the Apple icon and select System Preferences from the menu list.
In the System Preferences window, navigate to System section and click Speech option.
In the Speech window, mark the check box with label as Speak select text when the key is pressed.
The default key assigned for Text to Speech in Option+Esc. If you want to change the key combination the click Change Key button and assign your preferred key combination.