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The Five Factors that Contribute to Stuttering 
At least five factors contribute to stuttering. No single stuttering therapy is a "miracle cure"—or even more than moderately effective. Treating stuttering requires a multifactoral approach—different treatments for the five factors. The five factors are:
Auditory Processing Underactivity 
Brain scans have found that the auditory processing area is underactive during stuttering. It appears that stutterers can't integrate what we hear ourselves saying with how we feel our muscles moving. Electronic altered auditory feedback devices appear to correct this neurological abnormality. This factor is presented in the chapter Auditory Processing and Anti-Stuttering Devices.
Speech Motor Control Overactivity 
Brain scans have also found that the speech motor (muscle) control area is overactive. Stutterers overtense their respiration (breathing), vocal folds, and lips, jaws, and tongues (articulation muscles). These overtensed muscles lock up or fail to coordinate, making speech impossible. Fluency shaping therapy trains stutterers to speak with relaxed speech production muscles. This factor is presented in the chapter Speech Motor Learning and Control.
A third neurological abnormality associated with stuttering involves too-high levels of the neurotransmitter dopamine in the left caudate nucleus speech motor control area. This appears to contribute to speech muscle overactivity. Dopamine antagonist medications treat this abnormality. This factor is presented in the chapter Genes, Dopamine, and Anti-Stuttering Medications.
Response Selection to Stress 
Stuttering is a response to stress, but a response that sets up a vicious cycle. Personal construct therapy and other therapies train stutterers to handle stress in ways that result in fluent speech. This factor is presented in the chapter Response Selection Under Stress.
Psychological Effects 
Stuttering causes psychological fears and anxieties. For some individuals, these fears and anxieties are more disabling than their physical stuttering. Some individuals use stuttering as an excuse for deeper problems, such as inability to maintain relationships. Some individuals obsessively try to hide their stuttering, e.g., counterproductively refusing to go to speech therapy for fear that someone may see them entering the speech clinic. These individuals may need treatment with a psychologist in addition to speech therapy. This factor is presented in the chapter Psychological Issues.
Treating the Five Factors 
Most stutterers have one or two factors strongly. The other factors may be less significant. You might find a speech clinic that treats you successfully, especially if the speech clinic combines two or more therapies.
But a speech-language pathologist can treat at most three of the five factors. Electronic devices can treat one or two factors. Medications treat one factor. You'll likely have to go to several speech clinics, and possibly buy an electronic device or get a medication prescription, to treat all of the factors that contribute to your stuttering.
Additional Factors 
A sixth, seventh, eighth, and additional stuttering factors will likely be discovered. Likely other genes contribute to stuttering. The neurotransmitter acetylcholine might play a role.
Some advances in stuttering will be in the form of co-existing conditions. In other words, in the future children (and adults) will be tested for a variety of disorders, and treatment designed accord-ingly. E.g., a child with stuttering and phonological dysfunction will be treated differently than a child with stuttering and ADHD. An adult with stuttering and social phobia will be treated differently from an outgoing mentally retarded adult who stutters.
Stuttering Therapy Long-Term (In)Effectiveness 
Satisfaction with "Smooth Speech" Fluency Shaping 
In a study of a "smooth speech" fluency shaping stuttering therapy program, about 95% of stutterers were "very satisfied" or "satisfied" with their speech at the end of the treatment. A year later, their satisfaction dropped to 43%. (Craig, A., Calver, P. "Following Up on Treated Stutterers: Studies of Perceptions of Fluency and Job Status." Journal of Speech and Hearing Research, 34, 279-284, April 1991.)
ISTAR Comprehensive Stuttering Program 
A rigorous study followed 42 stutterers through the three-week program at the Institute for Stuttering Therapy and Treatment (ISTAR)  in Edmonton, Alberta, Canada.
The fluency shaping program was based on slow, prolonged speech, starting with 1.5 seconds per syllable stretch, and ending with slow-normal speech. The program also works on reducing fears and avoidances, discussing stuttering openly, and changing social habits to increase speaking. The program includes a maintenance program for practicing at home. The therapy program reduced stuttering from about 15-20% stuttered syllables to 1-2% stuttered syllables.
12 to 24 months after therapy, about 70% of the stutterers had satisfactory fluency. About 5% were marginally successful. About 25% had unsatisfactory fluency. (Boberg, E., & Kully, D. "Long-term results of an intensive treatment program for adults and adolescents who stutter." Journal of Speech and Hearing Research, 37, 1994 1050-1059.)
Attrition in a Long-Term Study 
A study of a "prolonged speech" stuttering therapy program had 32 stutterers initially speak about five times slower than normal speech, then gradually increase their speaking rate. Six subjects (19%) failed to learn the "prolonged speech" technique during the two-week residential therapy program. Eight subjects (25%) completed the residential training but refused to participate in a six-week, weekly therapy "phase II" program. Six subjects (19%) completed the six-week "phase II" program but refused to participate in the year-long "maintenance" program with infrequent therapy at the speech clinic.
One year later, the twelve subjects (38%) who stayed in the program were able to speak nearly fluently. Was this therapy program a success? 100% of the stutterers who completed the program were successful. But two-thirds of the stutterers didn't complete the program. (Onslow, M., et al., "Speech Outcomes of a Prolonged-Speech Treatment for Stuttering," Journal of Speech and Hearing Research, 39, 734-749, 1996.)
SLPs vs. Parents vs. Computers 
A study of 98 children, 9 to 14 years old, compared three types of stuttering therapy. The three types of therapy were:
- Intensive "smooth speech." This trained relaxed, diaphragmatic breathing; a slow speaking rate with prolonged vowels; gentle onsets and offsets (loudness contour); soft articulation contacts; and pauses between phrases. The children did this therapy in a speech clinic for 35 hours over one week.
- Home-based "smooth speech." This was similar to the first group, but parents were included, and encouraged to continue therapy at home. Therapy was done in a speech clinic for six hours once a week for four weeks (24 hours total).
- Electromyographic biofeedback. The children used an EMG biofeedback computer system about six hours a day for one week (30 hours total). The EMG system monitored the child's speech-production muscle activity. The children were instructed to tense and then relax their speech-production muscles. The goal was to develop awareness and control of these muscles. The children then worked through a hierarchy from simple words to conversations, while keeping their speech-production muscles relaxed. After mastering this while watching the computer display, the children did the exercises with the computer monitoring but not displaying their muscle activity. The speech pathologists did relatively little with the children: "Constant clinician presence was not necessary as the computer provided feedback as to whether the child was performing the skills correctly."
A fourth (control) group didn't receive any stuttering therapy.
At the end of each therapy program, all three therapies reduced stuttering below 1% on average.
One year after the therapy program, the percentage of children with disfluency rates under 2% were:
- 48% of the children from the clinician-based program.
- 63% of the children from the parent-based program.
- 71% of the children from the computer-based program.
The control group had no improvement in fluency.
The results for children with disfluency rates under 1% were even more striking:
- 10% of the children from the clinician-based program.
- 37% of the children from the "parent-based" program.
- 44% of the children from the computer-based program.
I.e., the computers were most effective, the parents next most effective, and the speech-language pathologists were least effective in the long term. At the 1% disfluency level, the computers and the parents were about four times more effective than the speech-language pathologists. (Craig, A., et al. "A Controlled Clinical Trial for Stuttering in Persons Aged 9 to 14 Years" Journal of Speech and Hearing Research, 39:4, 808-826, August 1996.)
Four years later, all three groups had average stuttering reductions between 76% and 79%. This may have been due to the more dysfluent children receiving additional speech therapy. (Hancock, et al. "Two- to Six-Year Controlled-Trial Stuttering Outcomes for Children and Adolescents," Journal of Speech and Hearing Research, 41:1242-1252, December 1998.)
Computer System for Reducing Short Phonation Intervals 
Another study had five stutterers use a computer that trains reduction of short phonation intervals. Normal speakers switch their vocal folds on and off many times each second, as they pronounce vowels and voiced consonants, such as /b/ and /g/, and then unvoiced consonants such as /s/ and /t/. A core stuttering behavior is an inability to quickly switch from voiceless to voiced sounds, i.e., to instantly switch on your vocal folds. The computer program trained stutterers to slow down that part of speech without slowing down other parts of speech (and so maintain natural-sounding speech). One year post-therapy all five subjects were able to speak nearly fluently. Larger clinical trials are scheduled for 2006. (Ingham, et al., (2001), "Evaluation of a Stuttering Treatment Based on Reduction of Short Phonation Intervals," Journal of Speech, Language, and Hearing Research, 44, 1229-1244.)
Two Long-Term Studies of Anti-Stuttering Devices 
A university provided delayed auditory feedback (DAF) anti-stuttering devices to nine adult stutterers. The stutterers used the devices thirty minutes per day. Three months later the subjects' speech had improved more than 50%, when they weren't using the devices (see Long-Term Effects of DAF).
Another study had eight stutterers use a hearing aid-style DAF/FAF anti-stuttering device five to eight hours per day for four months. The device improved the subjects' speech while they were wearing it, but no speech improvement was found when they weren't wearing the devices (see Long-Term Effects of DAF/FAF).
Stuttering Modification Therapy 
The above studies examined fluency shaping therapy programs. Fluency shaping focuses on physical speech production. Psychological treatment is a secondary part of therapy. The goal is to speak fluently and not stutter.
In contrast, stuttering modification therapy (sometimes called Van Riper therapy) focuses on psychological change. Reducing the physical manifestations of stuttering is secondary. The assumption is that stutterers will never be able to talk fluently, so don't let stuttering stop you from talking or doing what you want.
Only one study has examined stuttering modification therapy. Nineteen adult stutterers participated in the 3.5-week Successful Stuttering Management Program (SSMP, developed by Dorvan Breitenfeldt) program . Immediately post-treatment their speech had improved 10%. Six months later this modest gain had all but disappeared.
Several measures of anxiety found a 10-15% psychological improvement. The researchers cautioned that six months isn't a long follow-up, and that this psychological improvement might not last, given the absence of improved speech. The researchers concluded, "…the SSMP appears to be ineffective in producing durable improvements in stuttering behaviors." (Blomgren, M., Roy, N., Callister, T., Merrill, R. "Intensive Stuttering Modification Therapy: A Multidimensional Assessment of Treatment Outcomes," Journal of Speech and Hearing Research, 48:509-523, June 2005.)
Evidence-Based Practice 
The "No Child Left Behind" Act, Medicaid, and insurance companies now require healthcare practitioners to provide evidence for clinical decisions. This evidence is expected to be in the form of scientific research showing that a therapy is effective.
The American Speech-Language Hearing Association (ASHA)  is now promoting such evidence-based practice to speech-language pathologists. One of their goals is to develop clinical practice guidelines for each field, including stuttering. Some speech-language pathologists object to evidence-based practice. One speech-language pathologist questioned, "Does that mean that just because I haven't read any fluency articles [in scientific journals] that I don't know what I'm doing or I don't know what's good for my patients?"
But evidence-based practice doesn't mean that clinical decisions can be made only according to scientific research. ASHA's guide-lines also list two other factors: clinical expertise, and the goals and values of the client. "Clinical expertise" means that perhaps the speech-language pathologist in the last paragraph makes good judgments, despite never having read scientific research. (Banotai, Alyssa. "Emphasis on Evidence," ADVANCE for Speech-Language Pathologists & Audiologists, 15:46, November 14, 2005, page 7.)
And "goals and values" are important in treating stuttering. For example, a speech therapy program that is ineffective in producing fluency may be a good program for individuals whose goal isn't perfect speech, or who value the diversity of different people talking in different ways.
The most effective program (judging from these studies) appears to be ISTAR. Yet it was successful for only 70-75% of the stutterers. 25-30% of the stutterers weren't helped.
Stuttering Therapy Long-Term (In)Effectiveness 
Stuttering requires rest.
What Is Stuttering? 
Core Behaviors: Repetitions, Prolongations, Blocks 
Secondary Behaviors: Avoidances and Substitutions 
Childhood Stuttering 
Direct and Indirect Therapy with Preschoolers 
School-Age Stuttering and the Y Chromosome 
Fostering Teenagers' Passion for Fluency 
The Five Factors 
Auditory Processing and Anti-Stuttering Devices 
Delayed Auditory Feedback 
Frequency-Shifted Auditory Feedback 
Masking Auditory Feedback 
Sound Quality 
Background Noise Reduction 
Finding Help Paying for an Anti-Stuttering Device 
Speech Motor Learning and Control 
Slow Speaking Rate: The Path, Not the Goal 
Three Stages of Motor Learning 
Performing and Refining Fluent Speech 
Automatic, Effortless Fluency 
Reinforcing On-Target Speech 
Response Selection Under Stress 
Good Stress, Bad Stress 
Speech-Related Fears and Anxieties 
Personal Construct Therapy: You Always Have Choices 
Genes, Dopamine, and Anti-Stuttering Medications 
Dopamine Antagonists 
Antidepressants decrease Stuttering 
Other Medications and Drugs 
Psychological Issues 
Self-Awareness of Stuttering Behaviors 
You're Not Alone: Join a Support Group 
Freedom to Speak—Badly 
Inward Anger vs. Outward Anger 
Denial Is a Bigger Problem Than What You're Denying 
Famous People Who Stutter 
- James Earl Jones (actor)
- Mel Tillis (country music star)