Anti-Stuttering Devices

Our ears hear sounds. The central auditory processing area of our brains processes those perceived sounds into useful information, such as words. Central auditory processing disorder (CAPD) is not a single disorder but rather is an umbrella term for anything wrong with how our brains process auditory information. A wide variety of disorders seem to have a CAPD component, including ADHD and language disorders.(8) CAPD is not a hearing disorder, i.e., a person with CAPD usually has nothing wrong with his or her ears.

Brain scans have found that adult stutterers appear to have abnormal underactivity in their central auditory processing area. What's wrong with adult stutterers' auditory processing is unknown. If I had to guess, I'd say that stutterers have something wrong with how we hear our own voices. One study suggested that adult stutterers have an inability to integrate auditory and somatic processing,(9) i.e., comparing what we hear ourselves saying to how we feel our muscles moving.

If this is true, then stuttering is one of many sensory integration disorders (SID) that originate in childhood. Perhaps stuttering therapy should include exercises to train one to listen to one's speech and feel one's muscles moving.

Other CAPD Symptoms

I have other symptoms associated with mild CAPD. I prefer to watch movies with the subtitles on. I can't "pick up" foreign languages by ear; I have to study a written language before I can hear words, and then only if spoken slowly. If there's background noise, such as wind, I can't understand what people are saying.

Other symptoms of CAPD include sensitivity to certain noises; difficulty identifying the direction of sounds; difficulty following multi-step directions, especially if given in one sentence; and reading, spelling, and speech problems.

Altered Auditory Feedback

Changing how stutterers hear their voices improves fluency. This can be done in many ways:

• Speaking in chorus with another person.
• Hearing your voice in headphones distorted.
• Hearing a synthesized sound in headphones mimicking your phonation (masking auditory feedback, or MAF).
• Hearing your voice in headphones delayed a fraction of a second (delayed auditory feedback, or DAF).
• Hearing your voice in headphones shifted higher or lower in pitch (frequency-shifted auditory feedback, or FAF).

These phenomena are called altered auditory feedback. No brain scans have looked at stutterers' auditory processing while speaking with altered auditory feedback.(10) Hypothetically, introducing errors targeted at the area that integrates auditory and somatic processing increases blood flow to that area, increasing activity level to normal.

In other words, hearing what you're saying out of sync with what you feel your muscles doing raises a red flag. The red flag is raised in an area that's 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!"

Picture wagon trains, locomotives, and paratroopers descending on this sleepy little burg. In brain terms, more blood flows to this area.

The errors must not raise red flags in other brain areas, such as language processing. 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 stopped everyone—stutterers and non-stutterers—from talking.

Non-stutterers can't tolerate altered auditory feedback. I've amused many non-stutterers by putting an 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 and unexpected silent pauses.

Planum Temporale Abnormality and DAF

The planum temporale (PT) is an anatomical feature in the auditory temporal brain region. Typically people have a larger PT on the left side of their brains, and smaller PT on the right side (leftward asymmetry). A brain scan study found that stutterers have the opposite: their right PT is larger than their left PT (rightward asymmetry).(11)

A second study found that stutterers with this abnormal rightward asymmetry had significantly improved fluency with DAF, but stutterers with the normal leftward asymmetry didn't improve with DAF.(12) The study also found that stutterers with this abnormal rightward asymmetry stuttered more severely than stutterers with the normal leftward asymmetry.

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