Speech-Language Pathology/Stuttering/Core Behaviors
How Fluent Speech Is Produced 
Speech begins with breathing, also called respiration. Your lungs fill with air, more air than you would inhale if you weren't talking. You expand your upper chest and your diaphragm (belly) to get all this air in. Your lung pressure and respiration muscle tension increase.
Next, you release air through your throat, past your vocal folds (also called vocal cords). Your vocal folds are a pair of small muscles in your larynx. If you tense these muscles slightly, and release a little air, your vocal folds vibrate. This is called phonation. It's also called the fundamental frequency of your voice. If you place your fingers across the front of your throat, then hum or talk, you can feel your vocal folds vibrating.
Adult men vibrate their vocal folds about 125 Hz (125 times per second). Women vibrate their vocal folds about 200 Hz. Children's voices are even higher. This is too fast for your brain to control. Vocal fold vibration is the only muscle activity that your brain doesn't directly control. Instead, phonation results from the coordination of respiration muscles with slight tensing of your vocal fold muscles.
The key word in that last sentence was coordination. Stuttering is largely a disorder of poorly coordinated speech production muscles.
If you tense your vocal folds too much, you block off your throat and stop air from escaping your lungs. This is good when lifting heavy weights. By blocking your larynx muscles, you increase lung pressure, which strengthens your chest and you can lift more weight. Similarly, tires inflated to high pressure can carry a heavier car. But that's what stutterers do when they talk, and it's not a good idea.
The space in your throat above your larynx is called the pharynx. Above your pharanx are your oral and nasal cavities. These spaces create vocal resonation. This is like the echoing of a cathedral or tunnel. The unique shape of these spaces makes each of our voices sound unique.
Your jaws and lips, collectively called the articulation muscles, modify your voice into intelligible speech.
Vowels and voiced consonants (such as /b/ and /d/) are produced by your vocal folds, and modified by your articulation muscles (jaw, lips, tongue).
Other consonants are voiceless, such as /p/ and /t/, produced by your articulation muscles modifying airflow, without your vocal folds vibrating. When you whisper, you don't vibrate your vocal folds. You just modify airflow with your articulation muscles.
Speech requires coordination of over 100 muscles. The average person speaks about 150 words per minute. Each word requires a different configuration of most of those muscles. Speech is our most complex, balanced neuromuscular activity.
Core Stuttering Behaviors 
Core stuttering behaviors include:
- Disordered breathing, including antagonism between abdominal (belly) and thoracic (upper chest) respiratory muscles; complete cessation of breathing, and interrupting exhalation with inhalation.
- Disordered vocal folds, including high levels of muscle activity or muscle tension; poor laryngeal too late or holding tension too long; and poor coordination of laryngeal muscles, e.g., incompatible contractions of opposing muscles.
- Disordered articulation, including dysfunctions of the lips, jaw, and tongue in stuttering. In general, stutterers place their articulators in the right positions (in contrast to other speech disorders such as lisping, in which individuals form incorrect sounds), but time the movements wrong.
- Low-frequency tremors in the neck, jaw, and lip muscles of adult stutterers. These are found to a lesser extent in older children, and not found in young children who stutter.
Secondary Behaviors 
Secondary stuttering behaviors are unrelated to speech production:
- Physical movements such as eye-blinking, forehead wrinkling, sudden exhaustion of breath, frowning, or nostril quivering.
- Gross (large) muscle movements such as head jerks or slapping one's thigh in an attempt to release a vocal fold block or other overtense speech-production muscle.
- Avoidance of feared words, such as substitution of another word.
- Postponement of a feared word, with pauses or filler words.
- Interjected "starter" sounds and words, such as "um," "ah," "you know," or "in other words."
- Repeating a sentence or phrase "to get a running start."
- Vocal abnormalities to prevent stuttering, such as speaking in a rapid monotone, affecting an accent, or using odd inflections.
- Looking away from the listener, not maintaining eye contact.
- Articulating an unrelated sound, e.g., forming a /t/ sound when trying to say /s/.
Secondary behaviors may help you get around stuttering at first, but then lose their effectiveness. The secondary behavior is then retained out of habit.
Definitions of Stuttering 
Fluent speech can be defined in four parameters:
- Smoothness, or lack of interruptions.
- Speaking rate.
- Prosody, or emotional intonation.
- Mental effort.
Stuttering can be defined as:
- I. (a) disruption in the fluency of verbal expression, which is (b) characterized by involuntary, audible, or silent repetitions or prolongations in the utterance of short speech elements, namely: sounds, syllables, and words of one syllable. These disruptions (c) usually occur frequently or are marked in character and (d) are not readily controllable.
- II. Sometimes the disruptions are (e) accompanied by accessory activities involving the speech apparatus, related or unrelated body structures, or stereotyped speech utterances. These activities give the appearance of being speech-related struggle.
- III. Also, there not infrequently are (f) indications or reports of the presence of an emotional state, ranging from a general condition of "excitement" or "tension" to more specific emotions of a negative nature such as fear, embarrassment, irritation, or the like. (g) The immediate source of stuttering is some incoordination expressed in the peripheral speech mechanism; the ultimate cause is presently unknown and may be complex or compound.
An essential difference between speech and language disorders is that persons with speech disorders (e.g., stuttering) know what they want to say, but can't say it.
Stammering is the British word for stuttering.