This is fascinating to learn how we recognize faces. We don't recognize someone by memorizing his features like his eyes, nose and mouth.
With a great demo Artist/Teacher, Gary Faigin takes 2 different people and switches the feathers of the one on another's face. We still recognize this young man as we are aware of the SHAPES ON THE FACE not the eyes, nose and mouth. Maybe his mom might see the detail changes. Still we see his face.
It is great to watch this online workshop from Craftsy to learn the techniques of drawing or painting a likeness. Thank you Gary Faigin.