Stuttering Therapy Reviews

Stuttering High School Science Projects

DAF Effect on Stuttering
High School Science Project

Delayed auditory feedback (DAF) and frequency-shifted auditory feedback (FAF) devices immediately reduce stuttering 60-80%. DAF devices are used by speech pathologists for stuttering therapy with children and adults.

RadioShack.com sells DAF and FAF kits. The FAF kit is called a "Voice Changer" (990-0147, $14.95). It should be modified to use headphones or a headset rather than a speaker. Skill level is Moderate to Intermediate.

The DAF kit is called a "Mini Echo Mixer" (990-0239, $19.95). The delay length may not be long enough for speech therapy. One resistor must be removed to produce a single delay rather than an echo chamber. The kit does not include a microphone, amplifier (990-0011, $12.49), or headphones. Skill level is Intermediate to Difficult.

There are several alternatives to build a DAF or FAF device:

• Download DAF software.
• A DAF or FAF device can also be built using a guitar effects processor.
• Build the circuit below. The delay is adjustable from 4 milliseconds to over 200 milliseconds. The cost should be $25-50. Skill level is Intermediate to Difficult.
• Modify a "Voice Changer" toy to produce FAF. These make your voice sound like an alien or a robot. Wire out the speaker and wire in headphones.

Have your school's speech pathologist help with your experiments. She may know individuals who stutter, or you can call the National Stuttering Association at (800) 364-1677 to find volunteers. After you finish, your school's speech pathologist may want to keep the DAF device for therapy.

Experiments to do:

1. With a person who stutters, tape record the person's speech without the device; with DAF set at 50 ms (replace R7 with a 47K resistor, remove R8); 125 ms (replace R7 with a 100K resistor, remove R8); and 250 ms (replace R7 with a 220K resistor, remove R8). Count the number of disfluencies per minute, and the number of words or syllables per minute. Graph the relationship between fluency and speaking rate.
2. Have the person who stutters speak at a slow speaking rate, with and without the device. Again analyze fluency and speaking rate.
3. Do you agree with speech pathologist Janice Costello-Ingham, Ph.D., that
   

   the functional variable in regard to the reduction of stuttering is not DAF, but prolonged speech, and the latter can be produced without reliance on a DAF machine
   (Journal of Fluency Disorders, 18, page 30, 1993)

   or do you agree with speech pathologist Joseph Kalinowski, Ph.D., and colleagues that
   

   a slowed rate of speech is not a necessary antecedent for fluency improvement under conditions of altered auditory feedback
   (European Journal of Disorders of Communication, 31, page 259, 1996

   In other words, does DAF improve speech only when the stutterer talks slower, or does DAF improve speech at normal speaking rates?
4. Math and physics: measure and calibrate the delays in milliseconds for each setting of potentiometer R7. You'll need a frequency generator, frequency counter, and a dual-trace oscilloscope. Feed a sine wave into the DAF device. Set up the oscilloscope to display the input and output of the DAF device. At what frequencies do the two waves match? Find at least 3 matching frequencies for each setting of potentiometer R7. Divide 1 by the differences between the matching frequencies to get the delay length, in milliseconds. Find the settings for 50 ms, 100 ms, 150 ms and 200 ms. Explain why this works.
5. Use the DAF device on a person who does not stutter, at different delay settings. Is the DAF effect different on individuals who do or don't stutter?
6. Tape record a person who stutters speaking, for at least 3 minutes. Then have the person speak with DAF for 10 minutes. Take off the device and record another 3 minutes of speech. Do DAF cause a lasting improvement?

PARTS LIST

1. B1 9V battery
2. Battery clip
3. C1 1µF
4. C2 100µF
5. C3 100µF
6. C4 100pF
7. C5 0.1µF
8. C6 0.01µF
9. C7 220µF
10. C8 10µF
11. J1 3.5mm jack (microphone)
12. J2 3.5mm jack (headphones)
13. R1 10K
14. R2 4.7K
15. R3 470K
16. R4 220K
17. R5 47K
18. R6 4.7K
19. R7 1M potentiometer (Radio Shack #271-211)
20. R8 220K
21. R9 10K potentiometer (Radio Shack #271-215 includes on/off switch)
22. U1 HT8955A Digital delay computer (Radio Shack #900-7548)
23. U2 41256 256K DRAM memory (JDR Microdevices #41256-80)
24. U3 LM386 power amplifier (Radio Shack #276-1731)
25. U4 LM2931Z-5.0 voltage regulator (OK to substitute Radio Shack #276-1770 7805 voltage regulator)

Parts are available from Radio Shack, Digi-Key, JDR Microdevices, or other electronics suppliers. Parts cost should be under $20.

U4 can be any +5V voltage regulator. Radio Shack has the popular 7805 voltage regulator. Or order (from