Garr Reynolds recently discussed the power of faces on his blog, Presentation Zen. He explains that not only are we wired to see faces (both human and animal), but also that we notice of eye gaze (Source).
Think about eye gaze when designing your visual presentations. Since we immediately focus on the face before the text, use the face to guide your audience around your visual. Look at this example:
Since faces are the most powerful visual tool, our eye first focuses on the face. After processing the face, our eyes follow the eye gaze of the man in the picture. The flow of this image is simple, but it goes something like this: 1) face —> 2) eyes —> 3) eye gaze —> 4) text.
Garr Reynolds shows the power of eye gaze in an example similar to this one:
Faces are important in advertising, marketing, and slide design because our eye gravitates toward a face. Simply remember that eye gaze is important when placing text on a slide so that you can lead the audience visually in a way that flows well.