Let's take a few minutes to talk about
sign languages. I want to transmit to you
a few ideas about sign languages, which
are after all, languages that we could
process using NLP. The first one is that
sign languages are full languages. They
can express any idea just like spoken
languages, like English, like Spanish. You
can say anything in them. Sign languages
have their own grammars, but those
grammars are fully generative, just like
the ones that we saw in week 2 for
spoken languages. They can always
generate new sentences and express new
ideas, such as hang in there. This is an
example of American sign language, also
called ASL. Not only are they fully
generative and can they generate any
id - can they express any idea, but
there's also a lot of them, hundreds of
them. As you can see in this map, there's
many sign language families just as
there are spoken language families. For
example here in Britain we have a
British sign language which is related
to the sign languages in Australia and
New Zealand. We also have the French sign
language which is related to sign
languages spoken in Spain, and in some
parts of Latin America. There are many
sign languages. They're all
different from one another, just like
spoken languages are. For example, this is
the word tree in American Sign Language,
Danish sign language, and Chinese sign
language. You can see there - they're as
different this English, Danish, and
Chinese are from each other.
It's something very important is that
sign languages are not English.
There is fingerspelling. You might have
seen this where there is - there are lists of
how to convert a consonant or a vowel
from English, from written English into
an ASL sign. However most ASL signs are
not simply a conversion of English into,
you know, expressions with your fingers.
Most of them are words of ASL. And ASL
has - has its own grammar rules that are
very different from English. This is just
one example. For example, in English, verbs
use affixes express their tense. For
example, you have walk -ed walked, dance -ed danced. In ASL you also use a type
of conjugation, but this conjugation is
spatial. Signs that are related to the
past happen near to the torso and
tilting backwards; signs that have to do
with the future happen away from the
torso and tilting forward, as you can see
in the two examples here. So both
languages use morphemes attached to
roots to express time, but they use them
very differently. So ASL is not English
and it's just a full language on its own.
The main idea that I want to tell you
about is that sign language is not just
about hands. Sure, many signs are made
with your hands. However there's a lot of
other articulators involved. As - as I just told you, the position of your torso
for example, changes the tense of a word.
Your eyebrows in ASL for example can
indicate that you're asking a yes-or-no
question, or who what question. In these
examples of British sign language, the
closed mouth versus an open mouth
can indicate the difference between
battery and uncle which are otherwise
the same motions. For example, flat lips
versus pursed lips are the only
difference in the signs Brighton and
expensive. So things like the position
of your torso, your eyebrows, your lips,
those are also parts of words and sign
languages. And so it's not just using
your hands, and because of that whenever
someone tells you that they develop
gloves that can translate ASL into
English,
they're probably selling you snake-oil.
Sign languages again are not just about
your hands. They have to do with torso,
face, and interaction between all these.
It's not just about the hands or the
fingers. Finally, sign languages could be
written. There are several systems to
write sign languages. This is an example
of what the Goldilocks story would look
like. But sign languages are not written
very frequently. Usually when people
speak them, it's either signing, or for
example through videos. In summary, sign
languages are full languages with their
own grammars that are transmitted with
motions of hands, of - of your face, and
torso. Same as spoken languages use
motions of your lungs and your vocal
cords and your mouth to transmit the
ideas, sign languages use motions of
hands, of faces, and torsos to transmit
the ideas. They're different in that they
have their own grammars. They're human
languages in that they have the same
properties as spoken language. For example,
they're generative and can generate new
sentences all the time. There's many of
them. And in our next video we're going
to look at how we could use sign
languages with natural language
processing.
