PowerPoint can transcribe the speaker as the presentation is given, displaying on-screen as captions. Captions are an element of universal design for learning, removing barriers, and providing a benefit to many people. 

1. On the Slide Show ribbon tab, check Always Use Subtitles
    
2. In Subtitle Settings, choose the language you are speaking, and the language the subtitles will appear in (The default is English for both) 
    
3. To toggle the subtitles on and off, click the Toggle Subtitles button from Slide Show View or Presenter View, on the toolbar below the main slide