I believe the image below is a perfect example of both optical and psychological emphasis.  The use of the red stop sign draws the viewer to the image (use of optical) and since it is an object we are accustomed to seeing, it attracts us psychologically as well.  The twist associated with the image is the spelling of the word Stop (Stahp) which are mind immediately reacts to and though misspelled, our mind (psychologically) reads the word Stop!  Quite a concept.  You could also argue this image uses emphasis by contrast (the bright red sign against a blue background), placement (centering the sign in the image) and one element (the stop sign itself.)