Science Break
The field
of linguistics, specifically phonetics, compares phonemes according to
their actual physical attributes. The grouping does not really concentrate
on the visual aspects, as sounds rely on things going on in the throat and
in the mouth, as well as on the lips. But, perhaps this can help me
organize the phonemes a bit.
Sounds can be categorized according to voicing, manner
of articulation (airflow), and the places of articulation. There are more,
but these will get the job done. As speakers of English, we automatically
create sounds correctly without thinking about what is going on inside the
mouth. Yet, when we see a bad animation, we know it doesn’t look quite
right although we may not know why. With the information below, you will
be equipped to know why things look wrong. Now for some group
participation. This is an interactive article. Go on, no one is looking.
The categories we want to examine are:
Voiced vs.
Voiceless. Put your hand on your throat and say something. You can
feel an intermittent vibration. Now say, “p-at, b-at, p-at, b-at,”
(emphasizing the initial consonant). Looking at the face, there is no
visual difference between voiced and voiceless sounds. In some sounds the
vocal cords are vibrating together (b-voiced) and in some the vocal cords
are apart (p- voiceless). This is an automatic no-brainer as far as
reducing sounds into one viseme. Any pair of sounds that is only different
because of voicing can be reduced to the same viseme. In English, that
eliminates eight phonemes.
Nasal vs.
oral. Put your fingers on your nose. Slowly say “momentary.” You can
feel your nose vibrating when you are saying the “m.” Some sounds are said
through the nasal cavity, but most are said through the oral cavity. These
are also not visibly different. So again, we have an automatic reduction
in phonemes. All three nasal sounds in English can be included in the oral
viseme counterpart.
Manners of
Speech. Sounds can also be differentiated by the amount of opening
through the oral tract. These also do not offer a visible clue, but are
very important for categorizing phonemes. Sounds that have complete
closure of the airstream are called stops. Sounds that have a partially
obstructed closure and turbulent airflow are called fricatives. A sound
that combines a stop/fricative is called an affricate. Sounds that have a
narrowing of the vocal tract, but no turbulent airflow, are called
approximates. And then there are sounds that have relatively no
obstruction of the airflow; these are the vowels.
|
Figure 2. Side cut-out
view of places of
articulation. |
Places of
Articulation. This involves where the sound is being made in the
mouth. This is where the visible differences occur. There are several
places of articulation (see Figure 2) involving the lips, teeth, tongue,
and stuff in the back of the mouth (the palate, velum, and glottis) for
the consonants. Vowel placement is based on the relative height of the
tongue and whether the tongue is more front or back in the mouth. A
differentiating factor not listed in Chart 1 is lip rounding. This is not
associated with any particular place of articulation and will be addressed
below. Whew.
As I said, there are 35 phonemes in my dialect of
American English. You may have more. Chart 1 is a summary of these
phonemes. Read the chart from the front of the mouth to the back of the
mouth. Try saying each of the words that illustrate the phoneme that is in
bold. Have a look in the mirror and see what is going on as well as feel
what is going on inside the head. By using the distinction of voicing and
oral/nasal, we have already eliminated 11 phonemes. Let’s continue the
reduction of phonemes into the usable visemes.
Take It to the Limit
According to the chart, there are three bilabials,
which are sounds made with both lips. They are.
According to the Figures 3a, 3b, and 3c they have different attributes
inside the mouth. B and P only differ in that the B makes use of the vocal
cords and P does not. The M sound is nasal and voiced so it is similar to
the B sound, but it is a nasal sound. The cool thing about these sounds is
that while there are differences inside the mouth, visually there is no
difference. If you look in a mirror and say “buy,” “pie,” and “my” they
all look identical. We have reduced three phonemes into one
viseme.
 |
Chart 1. American
English phoneme summary
chart. |
While you’re working, remember that you are thinking
with respect to sounds (phonemes), not letters. In many cases a phoneme is
made up of multiple letters. So, if we go through Chart 1, we can continue
to reduce the 35 phonemes into 13 visemes. For the most part, the visemes
are categorized along the lines of the Places of Articulation (with the
exception of).
Take a look at the following listing of visemes. It
describes the look of each phoneme in American English. The only phoneme
not listed is. “In English, ‘h’ acts like a consonant, but from an
articulatory point of view it is simply the voiceless counterpart of the
following vowel.” (Ladefoged, 1982:33-4). In other words, treatlike
the vowel that comes after it.
Visemes
1.-
Closed lips.
2.&
- Pursed lips.
3.&
- Rounded open lips with corner of lips slightly puckered. If
you look at Chart 1,is made in the same place in the mouth as
the sounds of #7 below. One of the attributes not denoted in the
chart is lip rounding. Ifis at the beginning of a word, then it
fits here. Try saying “right” vs. “car.”
4.& [f
] - Lower lip drawn up to upper teeth.
5.&
- Tongue between teeth, no gaps on sides.
6.- Tip of
tongue behind open teeth, gaps on sides.
7.
- Relaxed mouth with mostly closed teeth with
pinkness of tongue behind teeth (tip of tongue on ridge behind upper
teeth).
8. [vision,
shy, jive, chime] Slightly open mouth with mostly closed teeth and
corners of lips slightly tightened.
9. [y, g, k,
hang, uh-oh] - Slightly open mouth with mostly closed
teeth.
10.
- Wide, slightly open mouth.
11. [bait, bet,
but] - Neutral mouth with slightly parted teeth and slightly dropped
jaw.
12.-
very round lips, slight dropped jaw.
13. [bat,
bought] - open mouth with very dropped
jaw. |
To see how helpful this information can be when
animating a face take a word like “hack.” It has four letters, three
phonemes, and only two visemes (13 and 9 in the listing).
Say that you don’t have enough space to include 13
visemes and whatever emotions you want expressed. Well, by using Chart 1
and the list of visemes in the listing, you can make logical decisions of
where to cut. For example, if you only have room for 12 visemes, you can
combine viseme 5 and 6 or 6 and 7 below. For 11 visemes, continue
combining visemes by incorporating viseme 7 and 9 below. For 10, combine
visemes 2 and 3. For 9, combine 8 with the new viseme 7/9. For 8, combine
11 and 13.
If I were really pressed for space, I could keep
combining and drop this list down further. Most drastic would be three
frames (Open, Closed, and Pursed as in boot) or even a simple two frames
of lip flap open and closed. In this case you would just alternate between
opened and closed once in a while. But that isn’t very fun or realistic,
is it?
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Art
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