We're going to be talking today about the models of speech production. Now why is
it important to understand the models of speech production? people try to simulate
different ways of how we actually produced speech in order to understand how we
produce speech. There are lots of theories on how we produce speech so people then
researchers end up testing those theories with models to see how we actually produce
speech. now its important to understand that because then we could say if there is an error in our speech production
process can a particular model support or help us find out where the error lies in the speech
production process if we knew how the speech was produced. does that make sense? all were
trying to understand is that are different models in speech production
everybody has a different way, they are tested different ways there is no one way to
produce speech there are different models and so determinating where im gonna end is going to say that the
combination of all of these models that are proposed that will help us understand
speech production. Before we understand that I said theories and I said models
so lets understand what is the difference between a model and a theory. When talking about a theory, a theory is just a
statement about a particular phenomena. when you propose that statement there are
certain underlying principles and assumptions that you will use to state that
particular phenomenon. so for example for me everything that comes up easily is my
financial system because I work with the financial system voice and lettings
most of the times. so one of the theories was that vocal folds vibrate
due to mass and stiffness present in somebody's body, which is the vocal folds.
so that was the theory that suggested that the vocal folds vibrate due to the presence of mass and stiffness.
Now this theory,
you can propose a theory and you can leave it at that but a theory can be tested
and the theory will be subject to change with more data. So for example if I propose
a theory that vocal folds vibrate because of the mass and stiffness present in its body, when I test the theory and I found that its not
really the stiffness, actually the new theory I should say it's not really the mass that
helps it is more the stiffness is what the new theory has come up. so a theory can be subjected
to change if we had more data and of course a theory can be tested. so if you've heard about theory on
gastric ulcers, if this was a class, I'd ask you what are some of the common causes of gastric ulcers and the first few things
that would come up is spicy foods, stress and things like that. those could be prespadating factors or those
could be aggravating factors of gastric ulcers but the main reason for gastric ulcers is
the presence of bacteria H pylori in your stomach wall that causes gastric ulcers.
So that theory which was because saying people because of the food that you eat, acidic or spicy food, or because of stress
those could be aggrevating factors to the theory change from the assumption that it was due to stress
to the assumption that it is because of the bacteria H pylori. see the difference?
so a theory is just a statement it incorporates underlying principles, a theory can be tested and the data you get from testing the theory
the theory can be subject to change. when we talk about a model, a model is a
simplification of a system. so for example if I talk about my vocal folds again, if I wanted to study the
vibration of the vocal folds, I'm gonna simplify the system, the system has a lot of things but, I'm gonna
simplify this vocal fold system into just a block of mass and a block of stiffness
and im gonna study how the block of stiffness and how the block of mass is going to
help my vocal fold vibration that becomes a model, that model is testing the theory,
the theory is that the vocal fold vibrate with stiffness and mass. Its a presentation of a phenomenon.
the key thing to understand with the model is it can be manipulated in a very controlled
manner. so i can keep the mass the same, I can vary the stiffness and see what happens to vocal fold vibration or I can
vary the mass, keep the stiffness constant and see what happens to vocal fold vibrationor I can vary both of these in
a very controlled manner to see what happens to vocal fold vibration. so I will be able to
manipulate this model in order to understand how I can simplify a system
as complex as the vocal fold vibration and arrive at understanding the phenomenon
of vibration. a model can be a physiological model, mathematical model, or mechanical model like the
two mass amount model or the sixteen mass model of vocal fold vibration was more a mechanical model that helped us
understand vocal fold vibration. a theory can be tested with a model and i have said here about the two mass model of vocal fold vibration.
the two mass model became a three mass model and then a sixteen mass model, a thirty-two mass model and so on so that theory kept changing with what
mass was required for the vocal fold vibration but a recent article said mass does not play a huge role in vocal cord vibration, which is very interesting after all these
years of research. so a theory is a statement about what you use as underlying
principles and assumptions, a theory can be tested, a theory can be changed
based on the data that we have. a model is a simplification of a system it helps us understand the phenomenon of what we want to study, the
key thing is it can be manipulated in a very controlled manner and it can test a theory with a model.
today what we are going to talk about is the models of speech production, so which means we're simplifying
this model of speech
production, were simplifying the system of speech production, were going to study how the
simplified system helps us understand and various ways of simplifying the
system as you can see where I talk about all of the different kinds of models and how does it help us learn
concerning speech production. but before we do that im going to adress about three issues I'm gonna bring about three
issuesthat need to be addressed by speech production models, those three issues are serial-order issue
degrees of freedom and context sensitivity problem.
so there are three issues anytime you look at the model of speech production you need to know if
those models of speech production are addressing all these three issues, only one of these issues, or more than one issue. So what is a serial-order issue?
Now to think about speech we are combining linguistic elements or phonemic elements in a sequence so for example
think about the phonemes |k|, |t|, and |ae| right. now I can use the same three phonemes in different
orders to produce different words for example cat is |c| |a| |t|, Tack is |t| |a| |ck| and act is |a| |c| |t|. you see how the
position whether its the initial, median or final has been interchanged in those three
different things. So speech
is how you string these phonemic elements or linguistic elements in a serial order. the order of how you put these phonemes
is going to determine how the word is perceived, if I wanted to say cat but I ended up saying act, I'm
missing the whole meaning of what I wanted to convey. so the order in which you're stringing these phonemic elements is very
important to convey the meaning of speech production.
that is what speech production is all about, you can make information in how
you produce your speech. the theory behind the serial-order issue, remember a theory is a statement with underlying assumptions, is speech
organization phonemic or syllable sized?
so are we saying since we have to just combine all these linguistic
elements in a certain order, is speech organization as simple as phonemic or syllable sized?
it can be tested with a model, and we can talk about which models that have addressed these issues
or which models have considered or taken in account these issues when we talk about
different models of speech production. so what does a serial order issue? speech a sequence of linguistic elements
right you're producing the phonemes in a certain order
to convey what we want to convey, if we change the order it is going to change the meaning of what we wanted to
convey.
The theory behind that is a speech organization phonemic or syllable sized.
issue that needs to be addressed? It's called the degrees of freedom
each muscle contraction if you think about how we produce speech, if you
think about how many articulators we move, how each of those articulators have different
muscles, go back to the anatomy of speech mechanisms and think about all those muscles in tongue
think about all of the muscles surrounding the lips, right the upper
lip elevators, the lower lip elevators, the upper lip depressors, the lower lip depressors, the retractors of the lip right? and then think about all of the
muscles of the palate, think about all the muscles of the soft palate, the velum, and think about how many
muscles need to be involved when you're producing a particular speech sound. it is not as simple as
just stringing different muscle contractions and producing those speech sounds, so when we talk about degrees of
freedom
each muscle movement is considered, or each muscle contraction is considered a single degree of freedom so think about how many degrees of freedom are going to be involved in all of those
muscle contraction that are going to be there to produce a particular speech sound. So for example if I had to produce the sound (makes sound) right, (that sound) involves vocal fold vibration.... I need the muscles
lips to come, I need the lower lip elevators and the upper lip depressors to bring my muscles together to bring closure. I need my velum to be closed because its
not a nasal sound, its an oral sound so think about all of these muscles. Each muscle that contracts is a degree of freedom. So imagine the enormous
degrees of freedom because of the various muscle
contractions that use different times of contractions, different directions of
contractions, different locations of contractions, so if I thought about allof those enormous
constructions, and if I thought about each degree of new freedom to be applied to each muscle contraction and
it had to be the sequence on my God that's just way too much right? So we
need to understand that we have to, if I would say do we need more degrees of
freedom or less degrees freedom to produce speech I would say we need to see less degrees of freedom to produce beach and not
more degrees of freedom meaning how can we combined these musclular contractions to be able to
decrease the degrees of freedom. ok, so far we have talked about two different issues that need to b
addressed in muscle I mean models of speech production. The first one is the
serial order issue. The serial order issue is when you have stringing of linguistic elements or
phonemic elements in a particular order. You have to produce a speech to make sense if you actually combine them in the
order that it would make sense. So if I wanted to say Cat, I have to put the phonemic elements in
the right order so that they would make sense. Now the next issue that we talked about is the degrees of freedom. A
single muscular contraction produced in a speech was called a degree of freedom. So
each muscular contraction is called a degree of freedom. So think about all those muscular contractions that happen and if I just did every muscular contraction in isolation to produce
particular speech sound, then there is going to be enormous degrees of freedom where
the contractions are going to happen in different times, or same times, or different
directions, or same directions of contraction, So our goal has to be to decrease the degrees of freedom and not increase the degrees of freedom. The third
The theories that talk about the degrees of freedom
The theories that talk about the degrees of freedom is Speech motor system programs, separate motor signals for each muscular
contraction, so which means from the brain you are getting different motor signals for each muscular contraction. So
imagine how many motor programs need to be there in your brain to provide for each muscular contraction, a separate motor signal. Another theory is
hierarchical muscular control, meaning
higher level controlling the lower level. a Hierarchy saying,
ok the fine muscle groups will do more while the gross muscle groups will do less. Another theory is how we can reduce the
degrees of freedom is if you can combine the muscles based on their function so if
you can combine all of the depressors
together together or all the elevators together or all the retractors together, that is one way of reducing the degrees of freedom. Another way
to look at it, or another
theory is that muscles work in groups but they do not work individually which I
think will make more sense because if you were thinking about each muscular contraction
happening individually for every single time, I think our speech will be really slow, I dont think there will be any coordinated speech, so
muscles have to work in groups rather than individually. So for the first thing that we talked about which is
the serial order issue the theory was speech organization's was syllable sized or phonemic sized. Then we talked about the
degree of freedom, and we said there are various different theories to address these degrees of freedom and some of them are here, muscles work in groups rather than individually there should be a reduction in the degrees of freedom if you combine the muscles in terms of function.
There is a hierarchical muscular control, or there are separate motor signals for each muscular contraction. And we will talk more about how certain
models tested these theories. Final thing is the
context-sensitivity problem. The contet
sensitivity's problem is very simple we talked about
coarticulation which is when two speech sounds are produced at the same time in order to achieve our final output. Like where you are moving different articulators at the same time to produce two different
speech sounds for example the example I gave was two, where my lip rounding is already happening when I'm producing the sound in order to make
sense because you don't want to go (makes sounds) because its not even going to sound like two. So context sensitivity is when sounds vary with context, so there is coarticulation. It varies with speaker, a
my rate of speech is pretty fast right?
my stress patterns are different and I have an accent so sound clarity is different, or
my sound production is different from how a native American English will produce speech
but with repsect to context even though my vowel sounds or
my stress patterns are sometimes different, you get the picture or I am to the most part at least I
consider for the most part that I am intelligible because I have this context thing. You understand me based on context. The key factor is that there is a lot of
variability in speech production. Speech production is not invariant. There is a lot of variability in speech production, so three factors
that we have talked so far include serial order issue, degrees of freedom, and
context sensitivity problems. These three issues will have to be addressed in models of speech production for us to
understand how we are producing our speech. So the model remember it depends critically on the assumptions of its formation.
so as I said, theory has underlying principles and assumptions, and then you are developing a model based on the theory. So which means what is the nature of input, what is the key assumption of that theory to help us
construct a model is very important. So for example, if I said vocal folds vibrate based on mass and stiffness of the vocal folds, In my input I need to have
a key assumption that the mass and stiffness are very important, so I have to use those as my input in order
to change anything to understand vocal fold vibration, so a model depends critically on the assumptions of its formation. The nature of input is going to be your key
assumption, so for example the mass and stiffness will be my key assumptions in understanding the vibration of vocal folds.
Overview of different models of speech production. There is something called a
connectionist model, there is something called a dynamic systems model, there is a feedback model, there are target models of speech production models and language
and behavior. There is a interrelation between speech production models and behavior, and there are certain newer models of speech production.
I want you to think what a model is. I want you to think about the three issues that a speech production model will need to address. They are the serial order issue, the
degrees of freedom and the context sensitivity problem. The degrees of freedom have to be reduced in order for us to have a
coordinated speech production, in terms of serial order we have to follow a particular order of combining our phonemes in order to make sense and with
context sensitivity is that our speech is so variable that it needs to account for
coarticulation, it needs to account for rate of speech stress factors or dialectical changes of a speaker.