How we See How
"Voice is nothing
but beaten air."
A Roman politician
named Seneca made this quote many years ago. We know from the Incredible
Vocal Journey that Seneca was right. Air is the "fuel" we need
to power the voice; our vocal folds and vocal tracts chop up and
shape this air into words. Without air, we could not speak or sing.
But we can't
see air, so how can scientists and doctors measure voices, and why
would they want to measure a voice anyway?
Suppose a person
is having some trouble with his or her voice, for example it's too
soft to hear well. The doctor may recommend some special exercises
to strengthen the voice. Wouldn't it be helpful to have a measurement
before starting the exercises, and then again, after a few weeks
of the exercises to see if there has been improvement? These are
called objective measures. In other words, the measurements
are based on more than the doctor's or the patient's opinion that
the voice sounds better after treatment.
There are now
many interesting gizmos and tools that provide objective examinations
of the voice. Here is a sample of those used today by scientists,
doctors and speech-language pathologists.
tool, abbreviated as EEG, measures how tightly the vocal folds are
touching one another. This is an example of a non-invasive technique
- no instrument enters the body.
To do an EGG,
two small disks are placed on either side of the neck. An mild electric
current passes between the disks. The way the signal between the
two disks behaves shows how much the vocal folds are in contact.
[Remember, the vocal folds coming together creates voice.]
The screen of
the EGG displays the signal. The more the tissues are in contact,
the higher the peaks. Do you also see some "valleys"? These represent
times when the vocal folds were separated. Likely, the person in
the photograph was breathing in air at that moment.
the our sound-producing organ, the larynx, is buried in the neck,
it isn't easy for doctors and scientists to watch it do its work.
Most of our organs, such as the heart or brain, are also buried deep
within the body, and for this reason, experts have worked hard to
develop imaging machines that allow us to visualize organs within
One of oldest
imaging technologies is x-ray. However, x-ray is of limited use in
studying vocal structures. Can you guess why? X-ray is helpful in
studying problems with bones of the body (for example, a break),
but most vocal anatomy is soft tissue. Only a single bone - the hyoid
- is part of the larynx.
Other, newer imaging
machines, such as the CT (computed tomography) and MRI (magnetic
resonance imaging), can give us pictures of the soft tissues of the
body. Within the last few years it has become possible not only to
look at CT or MRI images in two dimensions, but also to create three-dimensional
images of a person's vocal structures.
In a fascinating
set of studies, Dr. Brad Story imaged the vocal system using MRI
and CT. Look at the result of his work (right). The subject was saying "ah" (as
in the word, "hot") using an MRI. A sophisticated computer and special
software allowed Dr. Story to manipulate the original MRI images
after the scans were complete. In the picture at the right. Dr. Story
was able to divide the head and neck tissues, leaving the air space
of the vocal tract (as shown in the center of the picture).
shapes such as these, Dr. Story and his colleagues can get an accurate
understanding of how the body produces many sounds, such as "ah" and
Without the help
of videostroboscopy, you would not have been able to see the human vocal
folds at work in the Incredible Vocal Journey.
It is an often-used and important tool used by ear, nose and throat doctors
(otolaryngologists) for their patients with voice problems.
a frighteningly long word, the procedure is simple. A doctor puts
a steel rod between the lips and over the tongue, so that the tip
is near the back of the throat. A miniature video camera, light,
and magnifier are on the tip of the rod. With the tool in correct
position, the doctor can see on an attached monitor the vocal folds
moving. The machine also makes a video recording of the procedure
to add to the patient's medical record.
A "strobe" light
(yes, like the ones you see at school dances) is used to average
quick vibrations of the vocal fold cycles. This slows the movement
so the doctor can see the vocal folds while the patient makes easy
sounds - usually an "eeeeeeee". With this powerful tool, the doctor
can make many observations:
- Is the color
of the laryngeal tissues and vocal folds healthy? These tissues
are fleshy-pink normally, but irritated tissues are often bright
- Does the patient
have any growths or bumps that may be a sign of injury or disease
that interfere with speaking normally?
- Are the left
and right vocal folds the same shape and size? [If they differ
greatly, it could explain a rough sounding voice.] Do they come
together well, or are there gaps (which would leak air and give
the voice a breathy sound)?
- Do the vocal
folds vibrate in a healthy, predictable pattern?
vocal range profile, sometimes called the phonetogram, is like playing
a computer game with
your voice. It's a tool used to determine the upper and lower limits
of both your pitch range and loudness. Because every person's voice is
different, everyone's VRP is unique; some scientists call it a "voice
print" (the same idea that every person's fingerprint is unique).
is really just a computer loaded with specially-written software
and equipped with a microphone. To make a voice print, the
user sits in front of the computer (ideally, in a sound-proof
room), saying "ahhh" over and over at various pitches and
loudnesses. The computer "draws" on the monitor the sounds
of the user's voice.
at the VRP (left). Pitch (frequency) is measured from left
to right, with the lowest-pitched notes at the far left.
Loudness (intensity) is measured from bottom to top, with
the softest sounds near the bottom.
and loudness are graphed together, the shape is often like
a football. Notice that the user is more limited in how loud
or soft she can be when she is vocalizing near the limits
of her high and low pitches. In the comfortable "middle" of
the pitch range, she is able to produce a wide range of loud
and soft sounds.
your understanding of VPRs with a matching game.
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