FAQ #3 - Electronic Devices for Stuttering

August 22, 1995

Send comments to: kehoe@netcom.com

The author, Thomas David Kehoe, is owner of Casa Futura Technologies,
president of the San Jose chapter of the National Stuttering Project,
and a member of the American Speech-Language Hearing Association.


Delayed auditory feedback (DAF) delays your voice to your headphones a
fraction of a second (in the 25-250 millisecond range).

Frequency-altered auditory feedback (FAF) alters the pitch of your voice
in your headphones.

Laryngeal auditory feedback (LAF) uses a throat microphone to pick up
your vocal fold vibration.  The device then electronically alters the
signal into a buzzing sound, to sound more like your actual vocal fold

These types of auditory feedback enable vocal awareness and control,
immediately reduce stuttering, with no training or mental effort.(3)
Your voice sounds natural.  You just put on the headphones and talk.

These auditory feedback effects have suggested to researchers that
stuttering is caused by defective hearing, or an auditory
disfunction.(4)  However, despite decades of research, no such hearing
defect has been found.

A normal auditory function may contribute to stuttering, and explain the
effectiveness of the electronic devices.  The stapedius muscle reflex of
the middle ear muscle attenuates your vocal perception 5-15 dB.(5)  If
you can't hear your voice clearly, you can't control it.

Paradoxically, electronically altering your voice to sound like someone
else overcomes the stapedius muscle reflex.  You then hear your voice
clearly, control your voice, and talk fluently.

If you only stutter in certain situations, such as public speaking or on
telephones, a DAF, FAF, or LAF device may be all you need.

The effect is useful in stuttering therapy.  If your speech pathologist
taught you fluency shaping speech motor skills, but you're having
trouble using these speech motor skills outside the clinic, a DAF, FAF,
or LAF device gives you the vocal control to stay on-target.  If you
continually use your fluency shaping speech motor skills for many hours
of talking, you should be able to discontinue using the device and
continue to talk fluently.

A DAF, FAF, or LAF device can help you eliminate speech-related fear and
anxiety, such as fear of telephones.

Many stuttering therapies train you to use slow, prolonged speech.  A
long DAF delay and/or a lower FAF pitch slows down your speech.  The
goal is not for you to talk abnormally slowly forever.  Rather, the
slow, deliberate movements help you develop speech motor skills.  The
training should lead to fluent speech at normal speaking rates without
the device.(6)

A short DAF delay and/or higher pitch FAF can increase your speaking
rate, while improving fluency.  If you use DAF/FAF to talk faster, you
won't develop carryover fluency.  The DAF/FAF effect may even wear off,
and you'll stutter when using the device!

DAF, FAF, and LAF may be used occasionally without therapy.  The devices
should be used for extended periods only under the supervision of a
speech pathologist.


Biofeedback devices provide information to a user about physical
processes or behaviors.  These devices require training from a speech
pathologist.  The devices improve your awareness and control of physical
aspects of speech, or speech motor skills.

The devices usually provide visual feedback.  The visual feedback can be
a row of green and red lights.  Or it can be a computer display.  Some
devices even have video games.

The most widely-used devices are:

- Vocal amplitude rate-of-change devices train the loudness contour or
gentle onset fluency shaping speech target.  A smooth increase in vocal
volume at the beginning of each phrase, and a constant vocal volume
until the end of the phrase, indicates continuous phonation.

- Vocal pitch.  A low vocal pitch indicates relaxed breathing,
continuous phonation, and slow, prolonged speech.  A high vocal pitch
indicates high articulatory muscle activity, high respiratory muscle
tension, and fast speech.

- Respiration monitors show your breathing on a computer, from a strap
around your chest.

- Electromyographs (EMG) use three electrodes taped to your neck and jaw
to monitor speech-production muscle activity.  The device indicates when
your speech-production muscles are tense.  EMG therapy trains you to
talk with relaxed speech-production muscles.(8)


You and your speech pathologist should plan what an electronic device
will train you to do, and how you will phase out using the device.  For
example, you may follow this plan:

1) Learn fluency shaping speech motor skills from a speech pathologist.
Discuss your speech-related fears and anxieties with your speech

2) Use the device to enable these speech motor skills outside the
clinic.  At the same time, use the device to reduce speech-related fear
and anxiety.

3) Switch off the device for short periods of time, in relaxed
situations, and continue to use fluency shaping speech motor skills.
Increase the length of these periods, in more stressful situations.
When you can talk fluently anytime, anywhere, discontinue using the


The Computer-Aided Fluency Establishment and Trainer (CAFET) is a
computer-based device combining a respiration monitor and a gentle onset
monitor.  This combination trains seven fluency shaping motor skills.
Visual feedback includes video games.

After the CAFET trains you to talk fluently, it trains you to no longer
need the device.  At first, you see both a graphical display of the your
speech and text error messages.  After successfully completing a series
of exercises, your speech pathologist switches off the graphical
display.  You just read error messages when you make a mistake.  When
you don't make a mistake, you see nothing.

After successfully completing more exercises, your speech pathologist
switches off the real-time display.  You don't see anything until the
speech task is completed, and then error messages are displayed.

One study found that 92% of users were fluent two years after completing
the program.(9)


Casa Futura Technologies' biofeedback devices automatically reduce
auditory feedback as you improve your speech motor skills.

The devices monitor your speech through vocal pitch or electromyography.
When your speech is relaxed and slow, the device switches off the
auditory feedback.  When your speech is fast or tense, the device
switches on DAF and FAF, to slow your speech.

You try to relax and keep the auditory feedback off during
conversations.  When you can talk fluently without auditory feedback,
you discontinue using the device and continue to talk fluently.

One device is pocket-sized and wearable.  One device plugs into
telephones, or may be used in speech clinics or at home for practice.


- NYNEX provides Casa Futura Technologies telephone devices to
Massachusetts residents who stutter.  California, Minnesota, and Montana
telephone company approval is expected in 1996.

- State vocational rehabilitation programs may provide electronic
devices or speech therapy for unemployed adults who stutter.

- The Individuals with Disabilities Education Act (IDEA) helps children
with disabilities.  Ask your child's school principal or speech

- The IRS allows you to deduct speech therapy equipment on Schedule A,
if your total medical expenses exceed 7.5 percent of your adjusted gross

- Federal Supplemental Security Income helps low-income children with

- The Americans with Disabilities Act (ADA) requires some employers to
provide devices, and then reimburses some of these employers 50%.  You
should qualify if your job requires talking, and stuttering interferes
with your job.  You also qualify when applying for or seeking a promo-
tion to such a job.  You must ask the employer for a reasonable accom-
modation, such as an electronic device, speech therapy, or a different
work assignment.  Your employer is not allowed to suggest such an
accommodation.  The employer is required to provide the reasonable
accommodation, or find an alternative.  Smaller employers receive a tax
credit for half of the cost (Section 44 of the Internal Revenue Code).
The IRS may also give an employer up to $2400 for hiring you, under the
Targeted Jobs Tax Credit Program.  Call (800) 669-EEOC for the Technical
Assistance Manual of the ADA.

(3)Kalinowski, J., Armson, J., Stuart, A., Gracco, V., Roland-
Mieszkowski, M. "Effects of alterations in auditory feedback and speech
rate on stuttering frequency."  Language and Speech, 1993, 36, 1-16.  50
ms DAF and/or 1/2 octave FAF reduced stuttering approximately 80% 
during reading, while increasing speaking rate.  Brenaut, L., Morrison, S.,
Kalinowski, J., Armson, J.  "Effects of Altered Auditory Feedback on
Stuttering During Telephone Use."   Dalhousie University, Halifax, NS,
Canada. 55 ms DAF reduced stuttering 50%, DAF and FAF reduced 
stuttering 75%.

(4)Wolf, A.A., Wolf, E.G. (1959).  "Feedback processes in the theory of
certain speech disorders."  Speech Pathology and Therapy, 2, 48-55;
Mysak, E.D. (1960). "Servo-theory and stuttering."  Journal of Speech &
Hearing Disorders, 25, 188-195; Yates, A.J. (1963).  "Recent empirical
and theoretical approaches to the experimental manipulation of speech in
normal subjects and in stammerers."  Behaviour Research and Therapy, 1,
95-119; Butler, B.R., Stanley, P.E., (1966).  "The stuttering problem
considered from an automatic control point of view."  Folia
Phoniatricia, 18, 33-44; Webster, R.L. & Lubker, B.B. (1968).
"Interrelationships among fluency producing variables in stuttered
speech."  Journal of Speech and Hearing Research, 11, 754-766.

(5)Shlomo Sillman, The Acoustic Reflex  (1984).  San Diego: Academic

(6)Ryan and Van Kirk. "Establishment of fluent speech in 50 stutterers
using DAF and operant procedures." Journal of  Speech and Hearing
Disorders, 1974 Feb;39(1). DAF therapy reduced stuttering from an
average 9.2 stutters per minute to 0.2 stutters per minute in about 20
hours of therapy over four months.

(8)Two studies found a 40-70% reduction in stuttering 6-9 months after
5-20 hours of EMG therapy: Craig, Cleary, "Reduction of stuttering by
young male stutterers using EMG feedback," Biofeedback and Self
Regulation, 1982 September; 7(3): 241-55; Manschreck, Kalotkin,
Jacobson, "Utility of electromyographic biological feedback in chronic
stuttering: a clinical study with follow-up,"  Perception and Motor
Skills 1980 October; 51(2): 535-40.

(9) The "criteria for success" was less than 1.4% stuttered syllables,
at a speaking rate of 3.5 syllables per second.  At six months post-
therapy 82% of subjects met the criteria; at twelve months, 89%; at 2
years, 92%.  Reported by CAFET, Inc., 4208 Evergreen Lane, Suite 213,
Annandale, VA 22003.