more...Human Facial Expressions
on our ANIMAL Friends
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Figures 1 & 2. Are you looking at a sad and a laughing owl? Or, is your human bias towards
crediting birds and animals with human emotions at play here?
crediting birds and animals with human emotions at play here?
 Figure 3. Is this one angry bird? | While the exact mechanisms that created the bird faces in Figures 1, 2 and 3 are unclear, the results are anything but. Scowling eagles (Fig.3) have appeared in art for decades, an appropriate mood for a symbol of vigilance and authority. Here the eagle's lowered, downwards-oblique feather edge occludes the eye in a fashion that exactly mimics the human expression of anger. Ignore your idea that the beak is angry as well – it’s just a normal eagle beak, inflected by the powerful eye signal. The baby owl (Fig 1) reinforces the upwards oblique sad signal of the brows with droopy body language , and even the redness of the left eye seems to help. Finally, the rigid owl beak in Fig. 2 appears arced upwards in the laughing bird although it, of course, is not -- neither the beak shape, nor the eye slit would appear happy without each other. |
SCIENTIFIC ANATOMY vs. INTUITIVE ANTHROPOMORPHISM
In response to my last blog post, HUMAN Facial Expression on our Animal Friends, I received a very interesting comment from David Breaux Jr., who has spent years in industry working on creatures and characters:
“I’ve done a LOT of this kind of work for films, and it’s always interesting because not all animals have the muscles needed to make those faces and quite often in realistic CG animals riggers rig according to the real muscles. What becomes most important is recognizing how we, as humans, see a specific facial expression and translate that into the animal’s anatomy.”
David's remarks are exactly my point. When you consider what facial expressions will work on the faces of realistic animals, do you limit yourself to the creature's specific anatomy, or to do you create an expression that will look “right” to your audience? His bias, clearly is in favor of the audience – as is mine. Even trying to replicate animal anatomy literally, should one choose to do so, can become a fool’s errand. Take the three wonderful photographs in Figures 1, 2 & 3, which I found, naturally enough, by searching the internet for "angry", "sad", and "happy" birds. We don’t experience any hesitation in finding these bird photographs credible, communicative, and extremely engaging. Nor can I look at these – can you? – without assigning the proper emotional states to these faces instantly, effortlessly, and unambiguously.
And yet, a look at available anatomical diagrams of bird faces, like the one reproduced in Figure 4 (below), indicate no actual bird musculature (as dogs clearly have) capable of creating oblique upper eyelids, or reducing the bird's eye to a slit. We are left with several possibilities: these images have been Photoshopped; they are accidents of feather texture or camera angle, or there are muscles that no one has so far accurately described. I ask you - does it matter?
In response to my last blog post, HUMAN Facial Expression on our Animal Friends, I received a very interesting comment from David Breaux Jr., who has spent years in industry working on creatures and characters:
“I’ve done a LOT of this kind of work for films, and it’s always interesting because not all animals have the muscles needed to make those faces and quite often in realistic CG animals riggers rig according to the real muscles. What becomes most important is recognizing how we, as humans, see a specific facial expression and translate that into the animal’s anatomy.”
David's remarks are exactly my point. When you consider what facial expressions will work on the faces of realistic animals, do you limit yourself to the creature's specific anatomy, or to do you create an expression that will look “right” to your audience? His bias, clearly is in favor of the audience – as is mine. Even trying to replicate animal anatomy literally, should one choose to do so, can become a fool’s errand. Take the three wonderful photographs in Figures 1, 2 & 3, which I found, naturally enough, by searching the internet for "angry", "sad", and "happy" birds. We don’t experience any hesitation in finding these bird photographs credible, communicative, and extremely engaging. Nor can I look at these – can you? – without assigning the proper emotional states to these faces instantly, effortlessly, and unambiguously.
And yet, a look at available anatomical diagrams of bird faces, like the one reproduced in Figure 4 (below), indicate no actual bird musculature (as dogs clearly have) capable of creating oblique upper eyelids, or reducing the bird's eye to a slit. We are left with several possibilities: these images have been Photoshopped; they are accidents of feather texture or camera angle, or there are muscles that no one has so far accurately described. I ask you - does it matter?
Figure 4. Hummingbird Muscles - most muscles are designed to do physical work and are massive enough to be easily seen in dissections. That’s true of all the hummingbird body muscles seen here. The only muscles that appear on the face are those involved with manipulating the beak. If there are other muscles that can reshape the eyes, as in Figures 1 & 2, they escaped the investigations of Zhang, which is not surprising, as such muscles can be extremely tiny compared to the motor muscles of the body and beak.
I understand why the muscles of facial expression on animals are often poorly described. From my own experience dissecting a human face, facial muscles are diaphanous, tiny, and very difficult to isolate. Imagine dealing with the same issues on a hummingbird face! More to the point, there’s not much interest in this topic in the scientific community which might justify the extra work; the subject of animal emotion, in general, is a big black box.
Which leads me back to the birds. Since studying facial anatomy from available sources is often unproductive and possibly misleading, and since there are multiple examples of human-like expressions on bird faces which seem completely credible and realistic, why would CG artists not use their intuition, and their training with human faces to modify animated birds accordingly? Are viewers going to detect anatomical impossibilities, and reject the results? We humans are spectacularly sensitive to the expressive movements of realistic human faces, and efforts to create convincing digital versions run smack up against our discomfort with facial behavior that violates certain very strict norms (the Uncanny Valley). We are NOT similarly equipped to judge the faces of eagles, giraffes, wildebeests, or even cats and dogs, as we lack the sort of deep, hard-wired knowledge base we have developed for the human visage. When we look at eagles scowling, for example, we are unable to suppress our anthropomorphic instincts (“animals do like we do”) so we accept the eagle's scowl as credible and communicative of the human emotion of anger.
THE (NOT) WHITES OF THEIR EYES
 Figure 5 | One thing I know for certain – there is NO mechanism in animal eyes, bird or mammal, to open them extra wide, as seems to be occurring in Fig. 5. This is a strictly human phenomenon; no animal can display as much eye white as is appearing in the face of the terrified woman in Fig. 6. What we see in Fig. 5 is the light-colored iris of the bird's eyes, without any eye white (sclera) surround - but it looks the same to us. |  Figure 6 |
As a CG artist, it is important to understand the "Light Iris Illusion" when you want to create extra wide eyes on birds (Figure 5) or dogs (Figure 12), or other creatures. Here we need a diagram:
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Figures 7, 8 & 9 - All animal eyes share the same basic structure of a white eyeball (sclera), with a pigmented sphincter muscle (iris) surrounding a black spot (pupil), which is the hole through which light passes. The contraction of the iris widens the pupil aperture, while relaxation shrinks it, a sensitive response to the amount of light in the environment.
What’s unique about the human eye display is the large amount of sclera that is always showing, much larger in area than the iris/pupil. This arrangement is great for communication, as it allows us to track the direction of the gaze – upwards, downwards, or sideways - depending on how the iris sits on the sclera and it makes the various occluded shapes of the eye whites appear with clarity and precision. Animals don’t show any sclera at all (or, a trivial sliver), just pupil and iris. So the wide-eyed bird in Figure 5 is merely an optical illusion of a bird mimicking the human wide-eye pattern, not a startled bird.
It turns out that there is a huge variety of pigmentation in animal irises, greater than in people (see Figures 10 & 11). When the iris is very light, as in Figure 11, we get the Illusion that we are seeing lots of sclera surrounding a much smaller iris; it would never occur to us that we are merely seeing a very wide iris and pupil, with no sclera at all. Since a large amount of sclera above the iris combined with an open mouth creates the human expression of surprise, Figure 5 very successfully replicates that expression. Try to convince yourself that the bird’s eyes are neutral, not widened; it can’t be done, although it is, in fact, the case.
It turns out that there is a huge variety of pigmentation in animal irises, greater than in people (see Figures 10 & 11). When the iris is very light, as in Figure 11, we get the Illusion that we are seeing lots of sclera surrounding a much smaller iris; it would never occur to us that we are merely seeing a very wide iris and pupil, with no sclera at all. Since a large amount of sclera above the iris combined with an open mouth creates the human expression of surprise, Figure 5 very successfully replicates that expression. Try to convince yourself that the bird’s eyes are neutral, not widened; it can’t be done, although it is, in fact, the case.
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Figure 10. Close up of the eye of an eagle (left) and a horse (right). Note the dark irises and insignificant sclera; this combination
makes it harder for CG artists to mimic expressive human-like emotion through eye patterns.
makes it harder for CG artists to mimic expressive human-like emotion through eye patterns.
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Figure 11. Close up of the eye of a Great Horned owl (left) and a Siberian husky (right). Note the lightly-colored irises which are commonly read as eye whites and allow artists to create more compelling human-like expressions.
We’ll finish this month’s post with another example of the Light Iris Illusion with the trio of seemingly-startled dogs in Figure 12. Note that the dog on the right looks the most surprised, as his iris pigmentation is the lightest and, therefore, it mimics human eye white the most effectively.
CG Artists - A word to the wise : If you can choose whatever degree of eye pigmentation
you want for your critters - lighter is generally better.
you want for your critters - lighter is generally better.
Figure 12 - Seriously? Three "startled" dogs with mouths dropped open and eyes (seemingly) widened. Note the sliver of sclera in the two dogs on the left – it has no effect on the apparent degree of eye opening, as it does so decisively on people. The key variable is the lightness of the iris (light yellow for the dog on the right) combined with a relatively contracted pupil.
Credits: Figure 1: "Sad" Owl, FunnyBirdSite.com; Figure 2: "Laughing" Owl, animals-zone.com; Figure 3: "Scowling" Eagle, www.clipart-library.com; Figure 4: Hummingbird Muscles Illustration, Artist: Quingyang Zhang, www.pinterest.com; Figure 5: "Wide-eyed" Owl, cdn.earthporm.com; Figure 6: Terrified Woman photographed in the, Nightmares Fear Factory, located in Niagara Falls, Ontario, Canada - www.NightmaresFearFactory.com; Figure 7, 8 & 9: Sclera diagrams by the author; Figure 10: Close-up eagle eye, en.wikipedia.org; & close-up horse eye, en.wikipedia.org; Figure 11: Close-up owl eye, www.paws.org & close-up dog eye, www.walldevil.com; Figure 12: "Startled" dogs, www.Top10DogPictures.com.
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