Title: Why Dogs May Tilt Their Heads When You Talk to Them | Psychology Today
Headings: Why Dogs May Tilt Their Heads When You Talk to Them
Stanley Coren PhD., DSc, FRSC
Why Dogs May Tilt Their Heads When You Talk to Them
Surprisingly, a dog's muzzle may be blocking his view of part of our faces.

Content: Unfortunately, up to now, there has not been much research on this issue, although there has been some speculation. Some people have suggested that dogs tilt their heads to the side when we speak to them so that one ear can hear more clearly what we are saying. Others have suggested that it is a social signal—perhaps the dog recognizes that we respond to that particular posture in a positive way (because it is so cute), and therefore the dog adopts this position, because they are more likely to get smiles and rewards when they do. Source: SC Psychological Enterprises Ltd.
I suppose it is because I worked and did research in the area of sensory perception for many years that it dawned upon me that the reason some dogs tilt their heads when we are speaking to them has to do more with vision, rather than hearing and social endearment. Try the following simple experiment: Hold your fist up to your nose as in the figure here. Now, in effect, you are viewing the world with a head shape that has a muzzle like that of a dog. If you now look at a person's face, you will find that the muzzle will block some of your vision and reduce your ability to see the lower part of their face. Remember it is this part of the face, particularly the mouth region, which is a vital component of human emotional expressions.