Speech-Language Pathology/Stuttering/Childhood Stuttering/Auditory Processing
Brain scans of adult stutterers have found two abnormalities associated with stuttering.
One neurological abnormality is underactivity in the auditory processing area (this chapter). The other neurological abnormality is overactivity in the <a href="MotorLearning.shtml">speech motor control area</a>.
This combination of over- and underactivity may explain why the "conventional wisdom" told to stutterers is a contradiction of trying harder and relaxation, e.g. "try harder to relax."
No brain scans have done of stuttering children. We don't know whether these two neurological abnormalities cause stuttering or are caused by stuttering. It's possible that stuttering causes a child's brain to develop abnormally in these two areas. It's also possible that some children have one or both neurological abnormalities before they start stuttering, which cause them to stutter.
No one is certain exactly what's wrong with adult stutterer's auditory processing area. Stutterers have normal hearing, i.e., there's nothing wrong with our ears. A <a href="References.shtml#edn31">study</a> suggested that adult stutterers have an inability to integrate auditory and somatic processing. I.e., we may have an inability to compare what we hear ourselves saying to what we feel our muscles doing. This may explain why we have poorly coordinated speech muscle movements.
<a name="Anti-StutteringDevices">Altered Auditory Feedback</a>
Changing how stutterers hear their voices improves fluency. This can be done in many ways:
- Speaking in chorus with another person.
- Hearing your voice distorted.
- Hearing your vocal fold vibration (phonation) without hearing the articulation of your lips, jaw, and tongue.
- Hearing a synthesized sound mimicking your phonation (masking auditory feedback, or MAF).
- Hearing your voice delayed a fraction of a second (delayed auditory feedback, or DAF).
- Hearing your voice shifted higher or lower in pitch (frequency-shifted auditory feedback, or FAF).
- Switching your voice from one ear to the other twenty times per second (binaural switching auditory feedback).
Together these phenomena are called altered auditory feedback. No studies have investigated the effects of altered auditory feedback on stutterers' brains. My hypothesis is that introducing errors targeted at the area that integrates auditory and somatic processing increases blood flow to that area. Such errors disconnect how you hear your voice from what you feel your muscles doing.
I.e., hearing what you are saying out of sync with what you feel your muscles doing raises a red flag. The red flag is raised in the area that is abnormally underactive in stutterers. It's like a poor little overlooked village suddenly saying, "The British are coming! Eureka! There's gold in them thar hills! We've struck oil! Aliens have landed!"
You can picture wagon trains, locomotives, and paratroopers descending on this sleepy little burg. In brain terms, more blood flows to this area. The activity level increases to normal.
The errors must not raise red flags in other brain areas, such as language processing. E.g., I built a device that, when you walked up to Fred and said, "Hi, Fred," the device whispered in your ear, "Hi, Steve." It didn't improve fluency. It just stopped everyone—stutterers or non-stutterers—from talking.
When stutterers hear altered auditory feedback, something feels right. You realize that all your life something was wrong but you didn't know it. Speaking just feels natural, like this is how we're supposed to talk.
In contrast, non-stutterers can't stand altered auditory feedback. I've amused many non-stutterers by putting a DAF/FAF anti-stuttering device on them and telling them to count to twenty. Most can't get to ten. They repeat or skip numbers, or giggle uncontrollably, then rip the headphones off.
If my hypothesis is correct, then altered auditory feedback increases blood flow to non-stutterers auditory/somatic integration area, raising activity to an abnormally high level. Too much activity is as bad as not enough activity. Interestingly, the effects of too much activity in this area are somewhat like stuttering—repeating words, or not being able to get words out.
Immediate Effects of Anti-Stuttering Devices
The most effective types of altered auditory feedback are delayed auditory feedback (DAF) and frequency-shifted auditory feedback (FAF). Each reduce stuttering about 70%, immediately, without training, speech therapy, mental effort, or abnormal-sounding speech. You just put the headphones on and talk. Combined DAF/FAF reduces stuttering about 80%.
Some "experts" say that DAF always makes you talk slowly and monotonously. They say that you can talk slowly without DAF so the devices are unnecessary. But several studies have shown that DAF (and FAF) reduce stuttering at normal and faster than normal speaking rates. The first such study was published in 1993. This is yet another example of Ph.D. university "experts" who claim to be scientists but instead tout unscientiﬁc "old wives’ tales" and don't read the research journals.
70-80% is the average improvement found in dozens of <a href="References.shtml#edn32">studies</a>, with hundreds of stutterers. Rarely does DAF and/or FAF improve anyone's speech more than 90%, or less than 50%. If auditory processing underactivity were the only cause of stuttering, then DAF/FAF devices would make all stutterers 100% fluent. The 70-80% effectiveness shows that auditory processing underactivity is an important factor in stuttering, but not the only factor. To get closer to 100% fluency an anti-stuttering device has to be combined with speech therapy.
Should Adults Use Anti-Stuttering Devices?
The only treatment for the auditory processing abnormality is an altered auditory feedback device. No speech therapy can fix this abnormality.
Many people overcome stuttering by treating the other factors, e.g., fluency shaping therapy. But using an anti-stuttering device in conjunction with other therapies will make the other therapies easier, faster, and more effective. You'll then use your anti-stuttering device less and less.
Even if you have success with speech therapy and can talk fluently in most situations, there will be a few situations in which you stutter. Public speaking is usually that situation. You may want an anti-stuttering device for public speaking.
And I keep an anti-stuttering device plugged into my telephone. I pick up the phone and talk fluently. After a few calls my speech is improved for the rest of the day. Many <a href="#Subsidies">states</a> provide telephone-compatible anti-stuttering devices free.
Should Children Use Anti-Stuttering Devices?
Children under six shouldn't use anti-stuttering devices. Childhood stuttering therapy is usually 100% effective, so anti-stuttering devices are unnecessary.
Seven- to thirteen-year-olds can use anti-stuttering devices under the supervision of a speech-language pathologist or a parent trained by a speech-language pathologist, or for limited unsupervised uses such as a classroom presentation. If your child gets speech therapy in school only twenty minutes each week, buying a device can enable your child to do therapy at home for thirty minutes each day.
We don't know whether children who stutter have the same neurological abnormalities that adult stutterers have. Altering a child's brain activity might cause his brain to develop in a different way. Extensive use of an anti-stuttering device might cause the child's brain to develop normal auditory processing and the child would outgrow stuttering. But maybe extensive use of an anti-stuttering device would cause the child's brain to develop in another, unknown abnormal way.
Some anti-stuttering devices impair the user's hearing. Some devices occlude (block) the ear that the device is in. And some devices pick up, distort, and amplify <a href="">background noise</a>. If a child can't hear his teacher, he'll fall behind in school. He might get hit by a bus that he couldn't hear coming. Some users have reported symptoms of permanent hearing damage, such as ringing in the ears or pain from loud noises.
<a name=DAF>Delayed Auditory Feedback</a>
If you've decided not to try an anti-stuttering device, you can skip the rest of this chapter.
If you want to talk at a normal speaking rate, set the DAF delay between <a href="References.shtml#edn33">50 and 75 milliseconds</a>. Don't use a delay longer than 75 milliseconds unless you're using <a href="">slow speech</a>.
I've seen this scenario over and over. A stutterer gets a 50% improvement at 50 milliseconds. He gets a 75% improvement at 75 milliseconds. He sees that the dial goes up to 200 milliseconds. He thinks, "I'll crank up this baby! I'll redline it! I'll turn it up all the way to 200 milliseconds and I'll be 200% fluent!"
Wrong. 200 milliseconds is for talking five to ten times slower. You can force yourself to ignore a 200 millisecond delay and talk at a normal speaking rate. You can train your auditory processing to be even less active.
Did you read that? Used incorrectly, a DAF device might make your auditory processing underactivity worse! This may explain why some stutterers have reported that a DAF device lost effectiveness or <a href="Footnotes.shtml#ftn8">wore off</a>.
<a name="Long-TermDAF">Long-Term Effects of DAF</a>
Nine adult stutterers used DAF devices thirty minutes per day, for <a href="References.shtml#edn33">three months</a>. The thirty minutes consisted of ten minutes reading aloud, a ten-minute conversation with a family member, and a ten-minute telephone call. The subjects received no speech therapy.
Long-Term Effects of DAF
The device used was the <a href="SchoolDAF.shtml">School DAF</a>, made by Casa Futura Technologies (my company), with a binaural (two ears) headset. The subjects were allowed to set the delay where they wanted. Most selected delays around 100 milliseconds.
Before the three months of DAF use, the subjects stuttered on 37% of words, on average. When they put on the DAF device their stuttering dropped to 10%. I.e., the device improved their speech about 70%.
Three months later the subjects stuttered on 17% of words, when not using the DAF device. When wearing the DAF device they stuttered on 13% of words.
This shows that, when not wearing the devices, the subjects' stuttering diminished from 37% of words to 17% of words, or a 55% improvement. This is "carryover fluency." Put another way, the device trained the users to no longer need the device.
The increase (from 10% to 13%) in stuttering when wearing the devices wasn't statistically significant. Examining this more closely, stuttering when wearing the device increased only for "automatic speech," such as reciting days of the week, and for repeating words and sentences after the examiner. No change in effectiveness was found in conversations or in a "picture description" task. This suggests that any "wearing off" effects occurred in less-important speaking situations.
The "carryover fluency" effect was the same across all speaking tasks.
Two other studies combined speech therapy with a DAF device. One <a href="References.shtml#edn35">study</a> was of adults, the <a href="References.shtml#edn36">other</a> of children. Both studies found that combining DAF and stuttering therapy trained the subjects to speak fluently (less than 2% stuttering) and no longer need the devices.
<a name="FAF">Frequency-Shifted Auditory Feedback</a>
Frequency-shifted auditory feedback (FAF) shifts the pitch of your voice in your earphones. A FAF upshift makes you hear your voice sounding like Mickey Mouse. A FAF downshift makes you hear your voice sounding like a <a href="Footnotes.shtml#ftn10">gravel-voiced radio announcer</a> saying his station's call letters.
A quarter-octave pitch shift reduces stuttering about 35%. A half-octave pitch shift reduces stuttering about 65-70%. A full-octave pitch shift reduces stuttering about 70-75%.
Shifting pitch up or down is equally effective, in short-term studies, when the stutterer is wearing the device. But there may be a long-term difference between an up- or a downshift. FAF causes <a href="References.shtml#edn37">non-stutterers</a> to speak at a higher or lower vocal pitch, depending on whether the device is set for an up or down frequency shift. This higher or lower pitch vocal pitch results from changing vocal fold tension. In other words, FAF induces changes in vocal fold tension in non-stutterers.
FAF Stuttering Reduction
You'll see in the chapter on <a href="">speech motor control</a> that vocal fold relaxation is a primary target of fluency shaping therapy. I.e., putting on a FAF device might induce in seconds what takes weeks in speech therapy.
A <a href="References.shtml#edn38">study</a> found that my company's FAF devices, set for a half-octave downshift, didn't cause a change in vocal pitch in stutterers. But speech clinics have reported that my FAF devices induce vocal fold relaxation in stutterers. I've seen this myself. Usually stutterers need a greater pitch shift, between one-half and one octave down. Also the study used older headphones which lacked the bass response of today's headphones. I believe that a new study, using one-half or one octave downshifts (the gravel-voice) would find that the current devices induce vocal fold relaxation. I've also seen that FAF downshifts induce a slower speaking rate, similar to DAF. If this is true, then a FAF downshift should result in long-term carryover fluency and no longer needing the device.
Conversely, a FAF upshift (the Mickey Mouse voice) appears to induce vocal fold tension. And I've seen FAF upshifts induce faster speaking rates. If this is true, then a FAF upshift should result in poor long-term performance (e.g., no carryover fluency, and possibly "wearing off).
Types of FAF
All of the published studies of FAF used octave-scale FAF. Octave-scale FAF requires lots of <a href="Footnotes.shtml#ftn11">computing power</a>. My company's devices use octave-scale FAF. When you set my devices to a one-octave upshift, the 125-Hz fundamental frequency of an adult male voice is shifted up to 250 Hz. The 250 Hz first overtone of your voice is shifted to 500 Hz. The 500 Hz second overtone of your voice is shifted to 1000 Hz. And so on.
If you instead use a one-octave downshift, your 125 Hz voice is shifted in your earphones to 62 Hz. Your 250 Hz first overtone is shifted to 125 Hz, and so on.
Octave-Scale vs. Frequency-Compression FAF
But the tiny computers in hearing aids don't have enough processing power to produce octave-scale FAF. Instead, a simpler process uses <a href="Footnotes.shtml#ftn12">frequency compression/expansion</a> FAF. The upshift adds 500 Hz to your voice (or 1000 Hz or 2000 Hz, depending on the setting). Thus, your 125 Hz fundamental frequency is shifted to 625 Hz—more than two octaves up! Your 250 Hz first overtone is shifted to 750 Hz. Your 500 Hz second overtone is shifted to 1000 Hz.
When you switch frequency compression/expansion to downshift or subtract 500 Hz from your voice, your 125 Hz fundamental frequency vanishes. 125 Hz minus 500 Hz is nothing (there are no negative frequencies). The 250 Hz first overtone of your voice also vanishes. And the 500 Hz second overtone of your voice vanishes. You can only hear the weak third (1000 Hz) and higher overtones of your voice. When I tried a hearing aid-style DAF/FAF device, I heard my voice in my ear rise in pitch as the FAF was adjusted lower!
No published studies have investigated whether frequency compression/expansion FAF has an effect on stuttering. From what consumers and clinicians have told me, upward frequency compression FAF seems to have good immediate effects but poor long-term results. Downward frequency expansion FAF appears to have little or no effect on stuttering (in contrast, downward octave-scale FAF has excellent immediate and long-term results).
<a name="LongTermDAFFAF">Long-Term Effects of DAF/FAF</a>
<a href="References.shtml#edn39">Eight subjects</a> (four adults, four children) used a hearing aid-style DAF/FAF device about seven hours per day, for four months. The delay was set at 60 milliseconds and the FAF at 500 Hz up (about two octaves). The subjects received brief speech therapy, specifically to prolong vowels and use "starter sounds" such as "um" and "ah."
Long-term effectiveness of hearing aid-style DAF/FAF device
Like the <a href="#Long-TermDAF">three-month DAF study</a>, a small "wearing off" effect appears in the chart but isn't statistically significant.
Unlike the three-month DAF study, the "carryover fluency" effect is small and statistically insignificant. Did the 500 Hz upshift induce vocal fold tension and/or a faster speaking rate, thus canceling the long-term benefits of DAF?
Or does using an anti-stuttering device half an hour a day produces better long term results than using it seven hours a day (see <a href="">Practice Scheduling</a>).
<a name="MAF">Masking Auditory Feedback (MAF)</a>
If you have silent blocks, in which you can't make a sound, you'll want a device with masking auditory feedback (MAF). You push a button and the device pulls you out of the block.
MAF is a synthesized sine wave at your fundamental frequency. This sound fools your brain into thinking that your vocal folds are vibrating. Your vocal folds relax and start vibrating.
The Edinburgh Masker, popular in the 1980s, helped many stutterers improve their speech over time, until they no longer needed the device. Other stutterers found that the device "wore off" and became ineffective. Still other stutterers have used the device for more than twenty years with no carryover or "wearing off." No <a href="Footnotes.shtml#ftn13">research</a> investigated why the device had different effects on different people. My guess is that the device made users talk louder, which increases vocal fold tension, and some users habituated to speaking with too-tense vocal folds. For the users who developed carryover fluency, the device may have helped them overcome fears and anxieties, or they may have used the device to enhance stuttering therapy.
<a name="SoundQuality">Sound Quality</a>
Different anti-stuttering devices have different effects, due to differences in sound quality. It's like the difference between listening to Beethoven at a concert hall, or as a cellphone ringtone. It's also the difference between an effective and ineffective device.
Different anti-stuttering devices have different frequency ranges. Generally, the bigger the microphone and earphones, the wider the frequency range.
My company's devices have a flat frequency response from 60 to 5000 Hz. This is the range of human voices, plus additional low range for FAF downshifting.
In contrast, hearing aids usually have a frequency range of 200 to 7000 Hz. The frequency ranges typically aren't flat, but instead are tuned to sound best somewhere around <a href="References.shtml#edn40">3000 or 4000 Hz</a> (where most people lose their hearing). The devices can't reproduce the low range of human voices, especially the fundamental frequency of phonation that's key to stuttering therapy.
Monaural vs. Binaural Sound
Binaural (two ears) sound is <a href="References.shtml#edn41">25% more effective</a> than monaural (one ear) sound. Some devices can be either binaural or monaural. Other devices are monaural only.
<a name="Warranties">Warranties, Returns and Repairs</a>
Read price sheets and warranties carefully. Are there hidden charges? Are the extra charges refundable if you return the device? How long is your trial period for returning the device? Do you get a full or partial refund?
Toss the device onto a hard floor (before you pay for it!). How breakable is it? How long is the warranty? Are repairs covered in all situations, or excluded if it was your fault that the device broke?
How easy would it be to lose a device, especially for a child?
Ask about the company's return rates. My company's return rate is less than 1%. Some companies have much higher return rates.
<a name="BackgroundNoise">Background Noise Elimination</a>
Some anti-stuttering devices work well in quiet speech clinics, but are unusable in a noisy restaurant. A variety of features help solve the background noise problem.
Positioned correctly, a noise-canceling directional microphone eliminates background noise at the source. In contrast, the omnidirectional microphones in hearing aids pick up background noises louder than your voice.
A "push to talk" button also eliminates background noise. You push a button and the device switches sound on. You let go of the button and the sound switches off.
In noisy environments you're usually in a group. E.g., you go out to a restaurant with three friends. You'll talk one-fourth of the time. Most of the time you sit and listen, with clear hearing. When you have something to say, you push the button.
This also works well for a child in school, who mostly listens and occasionally is called on by the teacher.
Most anti-stuttering devices have high-frequency filters to reduce noise above your vocal range. Some devices have adjustable filters, so that a man with a deep voice can set his device to filter out more background noise than a woman or a child with a high voice.
Voice activation switches on sound when the user talks, and switches off sound when the user stops talking. That is, if the device has a noise-canceling directional microphone. If the device has an omnidirectional microphone, loud noises switch on sound.
My company's Pocket Speech Lab analyzes your vocal fold tension and switches on DAF/FAF when you tense your vocal folds, before you stutter. It switches off sound when you're speaking with relaxed vocal folds, or not talking (see <a href="">Vocal Frequency Biofeedback</a>.
Some devices have dynamic expansion. This makes loud sounds louder and quiet sounds quieter. If you're using a noise-canceling directional microphone this makes your voice louder and background sounds quieter. With an omnidirectional microphone it can make your voice quieter and background noise louder.
Listening to someone talk, while you wear a DAF device that's picking up the other person's voice, is like reading the following:
That says, "difficult to hear another person speaking." You hear the person speaking twice, with the words out of sync.
In contrast, small FAF pitch shifts, without a DAF delay, have little impact on your ability to <a href="References.shtml#edn42">hear</a>. It's like hearing music played on a violin vs. on a viola. Or hearing your friend's voice drop a little when recovering from a cold. This is known as "acoustically transparent."
<a name="Subsidies">Finding Help Paying for an Anti-Stuttering Device</a>
Many states, including Texas, California, Massachusetts, Georgia, Wisconsin, North Carolina, and Arizona have <a href="discounts.shtml">special telephone equipment distribution programs</a> that provide telephone-compatible anti-stuttering devices free to qualified residents.
If you're employed, ask your employer to help pay for an anti-stuttering device. All of my customers who've asked their employers received help. And then they were given extra work and responsibilities. Some also got raises.
If your employer were to say no, you could mention that the <a href="">Americans with Disabilities Act</a> requires employers to pay for "reasonable accommodations" requested by employees with disabilities.
If you're unemployed and stutter, your state's vocational rehabilitation program will help get you a job, including paying for speech therapy and/or an anti-stuttering device. See the section <a href="">Vocational Rehabilitation</a>.
Some speech clinics will handle your insurance billing for anti-stuttering devices. The CPT/HCPCS procedure code for electronic anti-stuttering devices is E1399-NU. The diagnosis code for stuttering is 307.0.
I've had good experiences with Sertoma and Lions Clubs. Sertoma assists persons with speech, hearing, and language disorders. Service organizations prefer to help low-income children, and they prefer to be approached by the child's speech-language pathologist.