Speech-Language Pathology/Stuttering/High School Science Projects

Altered Auditory Feedback

High school students can build an altered auditory feedback device for a science project. Several alternatives are also possible:

  • Find a DAF kit by doing a websearch for "delay echo reverb kit."
  • Find a FAF kit by doing a websearch for "voice changer kit." Or rewire a voice changer toy (about $20) to use headphones instead of a speaker.
  • Find a MAF kit by doing a websearch for "function generator kit." MAF uses a 105 Hz sine wave.
  • Guitar effects processors usually have both reverb (DAF) and frequency-shift (FAF) effects.
  • Writing your own DAF software is easy. FAF software is harder, as it requires a fast Fourier transformation (FFT) for octave-scale FAF. DAF/FAF software can be downloaded for about $30 from http://www.artefactsoft.com.
  • Set up a computer to measure and display your vocal amplitude and frequency. Use a Radio Shack multimeter with a frequency counter and computer output. With a microphone the total cost should be $100-150. Or look for audio recording software with frequency analysis.

You can do the following experiments on yourself, or find volunteer subjects in your stuttering support group. Ask your speech-language pathologist to help you find a support group, or call the National Stuttering Association at (800) 364-1677. Experiments to do:

  • Tape record a stutterer's speech at fast and slow speaking rates, without the device; and then with DAF set at 50 ms, 100 ms, and 200 ms. Count the number of disfluencies per minute, and the number of syllables per minute. Graph the relationship between fluency and speaking rate.
  • Do you agree with speech-language 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"[1] or do you agree with speech-language pathologist Joseph Kalinowski, Ph.D., that "a slowed rate of speech is not a necessary antecedent for fluency improvement under conditions of altered auditory feedback."[2] I.e., does DAF improve speech only when the stutterer talks slower, or does DAF improve speech at normal speaking rates?
  • Math and physics: measure and calibrate the delay control of a DAF device. 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 three matching frequencies for each DAF setting. Divide one by the differences between the matching frequencies to get the delay length, in milliseconds. Explain why this works.
  • Use the DAF device on a person who does not stutter, at different delay settings. How is the DAF effect different on individuals who don't stutter, and persons who stutter?
  • Tape record a stutterer speaking (without DAF) for at least three minutes. Then have the person speak with DAF for ten minutes. Take off the device and record another three minutes of speech. Does DAF cause carryover fluency (after removing the device)?
  • Show how to use a vocal amplitude display to help you do gentle onsets. Show how vocal frequency is a surrogate for vocal fold tension, i.e., relaxed vocal folds produce a low vocal frequency, and tense vocal folds produce a high vocal frequency.
  • Find out if any of your relatives stutter. Draw a family tree showing your relationship to the person. Present evidence that stuttering has a genetic cause, and evidence that stuttering is not genetic.
  • Find a speech clinic that has a speech biofeedback system. Write a report about what the biofeedback system does.
  • Repeat Wendell Johnson's 1937 studies of adaptation and anticipation. These studies are described in A Handbook on Stuttering, by Oliver Bloodstein.


  • Write a report on the history of stuttering therapy, using Stuttering: The Search for a Cause and Cure by Oliver Bloodstein.
  • Write a report about a famous person who stutters.


  • Interview a speech pathologist about the cause of and treatments for stuttering. Describe the techniques and goals of two therapies. Ask your school district if they have a speech pathologist specializing in stuttering, or call the Stuttering Foundation of America at (800) 992-9392 to find a stuttering specialist.
  • Help your school's speech pathologist organize a "Youth Day," with the help of Friends Who Stutter or the National Stuttering Association. This is a weekend workshop in which a childhood stuttering specialist trains school speech-language pathologists and parents to treat stuttering. At the same time, the children play speech therapy games and meet each other.
  • Observe a speech pathologist treating a preschool child who stutters. Write a report about this, answering these questions: What games did the speech pathologist play with the child? What was the purpose of the game? What did the speech pathologist talk about with the child's parents?
  • Interview a successful adult who stutters. This could be an accountant, a lawyer, or a teacher. You can find such a person by calling a local stuttering support group. Ask how stuttering affected the person's childhood and high school years; adult life; choice of career; and marriage or relationships. What stuttering therapy has the person had? How severely did the person stutter when he or she was younger? Are there situations in which he or she stutters more, or stutters less? Are there are speaking situations he or she fears or avoids because of stuttering?
  • Does another student have a disability? Compare yourself to a student with a physical disability, and to a student with a non-physical disability (e.g., mental, emotional, or learning disability). See The Disability Hierarchy.


  1. ^ Costello-Ingham, J. Journal of Fluency Disorders, 18, 1993, page 30.
  2. ^ Kalinowski, J. European Journal of Disorders of Communication, 31, 1996, page 259.