Theories of Cause

original author: Tracie Randolph, former student
revised by: Cindy S. Spillers, current web master

Stuttering has existed since the earliest recordings of human history and so have ideas about what causes it. The search for a cause of stuttering has remained a great mystery and has yet to be solved. The search for answers has led many researchers down different paths of explanation as to what predisposes, or sets a person up to stutter, what precipitates, or brings out stuttering in a person, and what perpetuates, or keeps it going once it begins. It is important to keep in mind that currently there is no known cause of stuttering. Stuttering probably has more than one cause and these causes probably have a variety of factors involved in them. Following are some current ideas on the causes of stuttering.

Predisposing Factors

Predisposing factors are those things that set a person up so that, if conditions are just right, they will stutter. Many predisposing factors could also be consider risk factors, some of which are discussed in the section on incidence and prevalence of stuttering.

In the 1930s Robert West presented the idea that people who stutter have an organic predisposition to stutter. They inherit this predisposition in the form of an organic deficit which he called "dysphemia." In West's view, stuttering constituted an outward symptom of this inner dysphemia. How much dysphemia a person inherited depended on how many stuttering relatives they had. Inheriting dysphemia, in and of itself, was not enough to cause stuttering. West believed that the stuttering was precipitated by external factors such as speaking pressure, illness, or trauma. Advancements in scientific research have uncovered mounting evidence to support Robert West's original theory. Many modern views of stuttering have elements that hearken back to West's ideas of heredity, organic predisposition, and environmental factors.

Regarding the organic predisposition, we have had long standing evidence that stuttering runs in families and may be genetically inherited. Recent research on family pedigrees of people who stutter suggest that stuttering is inherited in two parts, possibly on two separate genes. First a person may inherit a predisposition to stutter. With this predisposition the child will stutter at some point in childhood of conditions are right. Second the person independently may inherit tendency to persist in stuttering or to recover. Some families have a greater number of people who recover from their stuttering while others have a greater number of people who persist. If a family history leans toward recovery, then chances are greater that a child who begins to stutter will outgrow the stuttering at some point. If the family history leans toward persisting, then the child has a greater likelihood of persisting, as well.

Precipitating Factors

Precipitating factors are often viewed as trigger factors, or conditions that set the predisposition into motion. Some of the theories in this category attempt to explain what the inherited stuttering genes control. Two current notions that try to explain what may trigger stuttering are called the Breakdown Hypotheses and the Demands-Capacities Model.

Breakdown Hypotheses

The Breakdown Hypotheses suggest that something is wrong with the physical make up of the person who stutters. These weaknesses can be attributed to genetic factors or could be acquired through accidents or surgery. Such breakdowns can happen in two domains: the cerebral dominance of the brain for controlling speech and language and the auditory feedback loop.

According to the Cerebral Dominance Theory, the language processing center is normally located in the left hemisphere of the brain. Therefore, the left side of the brain is the dominant side used for processing speech. In the person who stutters however, one of three things could be happening: the hemispheres of the brain are struggling to gain dominance of the speech center, the speech center is located in the right hemisphere which is inadequate for processing language, or the pathways for speech start in the left hemisphere and take a jog through the right hemisphere, rather than staying on the left side of the brain.

Recent research using new techniques for imaging the brain give a clearer picture of what happens in the brain when a person stutters. These imaging techniques show that people who stutter have greater amounts of activity in the right hemisphere when they talk compared to non-stuttering people. Since the left hemisphere is more efficient at processing speech and language, activity in the right hemisphere suggests that the brain uses inefficient pathways for talking. This inefficiency shows up as hesitations, repetitions, blocks and other behaviors that we associate with stuttering. In addition, the right hemisphere seems to be the relay station for emotions such as anxiety, fear, and excitement. The emotional and speech circuits may intersect and interfere with each other. Evidence from other brain research suggests that when two right hemisphere or two left hemisphere tasks get carried out at the same time, they will inhibit each other. This may be the physical phenomenon behind the proverbial expression that a person can't walk and chew gum at the same time. When applied to talking, the person who stutters may have inefficient pathways that go into the right hemisphere and intersect with some of the emotional pathways. This could explain why stuttering seems to make its first appearances when a child is excited or anxious. It could also explain why people who stutter often experience heightened fear and anxiety during moments of stuttering.

Children who recover from stuttering may have brains that reorganize the speech pathways, allowing them to develop more efficient routes for talking. People who persist in stuttering may not be able to reorganize their brains, causing them to continue in life with inefficient pathways for talking. In addition, some research on adults stutterers who have successfully completed therapy shows that these adults use more of the left sides of their brains when talking. Therefore, therapy may inadvertently help a person reorganize the pathways for speech in the brain.

The Auditory Feedback Theory suggests that the person who stutters has a breakdown in their hearing mechanism which allows them to hear their own speech a few milliseconds later than normal. The speaker's concentration and timing of their speech is thrown off because they are being bombarded by an echo of what they just spoke moments before. This delay causes the speaker to be dysfluent. The low incidence among the deaf sparked the original ideas that lead to research on the auditory feedback loop. If deaf people are less likely to stutter than hearing people, the cause for stuttering may lie somewhere in the hearing mechanism.

Evidence for this theory comes from research that alters the auditory feedback signal in one of two ways: by covering it up (using a masking noise) so the person can't hear it, or by altering the timing of the feedback so that the induced delay cancels out the original delay that the person may have. Both lines of research have suggested that masking or altering the timing of the auditory feedback helps the stutterer speak more fluently, at least temporarily. When the masking noise is removed or when the feedback is returned to its normal timing, the stuttering returns. Not all people who stutter have improved fluency under conditions of masking or delayed auditory feedback, however, indicating that this theory does not adequately explain the cause of stuttering in everybody.

Demands-Capacities Model

The Demands-Capacities model provides a simple and handy way to explain how stuttering might begin and develop in young children. It has the potential to encompass genetic predisposition, the sex ratio, personality variables, environmental factors, spontaneous recovery, and persistence.

The basic premise of the Demands-Capacities model suggests that children have developing capacities for speaking fluently. Two year old children would have less capacity for fluent speech than five year old children. At the same time that a child's capacities for fluent speech grow and develop so do the demands for fluency develop. Five year old children have greater demands placed on them for fluent verbal communication than do two year old children. Most of the time the capacities and demands for fluent speech stay in balance. Sometimes the demands will exceed a child's capacities, resulting in a period of dysfluency. When the demands chronically outweigh the child's capacities for fluency, conditions are ripe for the development of stuttering in the child. If the demands are cut back temporarily, giving the capacities a chance to catch up, the child may recover from stuttering.

Capacities for fluent speech seem to be largely internal and would include things like neurological development and muscular coordination. Additional capacities might include the ability to move muscles rapidly, like the movements required for talking; the ability to react rapidly to stimuli, including giving information quickly when asked; and the ability to plan and carry out a sequence of movements, like those required to say a long message. Finally, word finding skills may enhance a child's fluency. As children learn more and more words, they need to store these words in their brains and then get quick, easy access to them when they need them. The ability to retrieve words quickly and efficiently will help a person's fluency. Difficulty retrieving words will lead to more dysfluencies.

Demands for fluent speech can be internal or external. Internal demands might include the fast growing language skills of the child. As the child's vocabulary grows, s/he has more words from which to choose, placing higher demands on the word retrieval skills. As the child's expressive language skills develop, the child wants to express more complex ideas in longer and more complex sentences. As pragmatic skills develop, the child needs to learn how to take turns, how to say appropriate things rather than saying what ever pops into her/his mind, and how to take more responsibility for initiating and keeping a conversation going. All of these these linguistic skills can tax fluency by requiring the child to express her/himself quickly, appropriately, grammatically, and thoroughly.

External demands also come into play. These can include the linguistic behaviors of others, such as rate of talking and pace of turn-taking in a conversation. They can also come in the form of expectations for clear articulation, accurate grammar, and quick relaying of information on the part of the child. General life-style expectations can also become demands for fluency. A generally fast paced life style, where everything must be done quickly because the family has so much to do and so many places to go in a day, can lead to a general increase in tension and anxiety in a child who doesn't have the neurological or physical capacities for quick reactions and movements. This anxiety and expectation for quickness can spill over into the talking domain.

When the demands for fluency chronically outweigh the child's capacities for fluent speech, the child might react to these situations by trying harder to get her/his words out faster. The child might force the words out and struggle on them, push them out with more air pressure, or tense the speech muscles, making them stiff. Ironically all of these behaviors that the child does in an attempt to get her/his words out faster end up making the speech muscles slower and less coordinated and making the words come out slower. Parents may react to these episodes of tense and uncoordinated speech with alarm or disapproval, making the child want to try even harder to talk quickly and smoothly.

The Demands-Capacities model suggests that these episodes of tension and struggle with talking happen during the time when children are learning to talk semi-automatically: they are having to think less about how to talk and can think more about what they want to say. The patterns of tension and struggle that the child uses and the emotional reactions to the struggle can become habituated as the child's pattern of talking. If this habituation happens, the child will stutter. If, however, the demands for fluent speech are lessened during this phase, giving the child's capacities a chance to catch up to the demands, the period of tension and struggle may be temporary and the child may recover, going on to develop normal fluency.

Perpetuating Factors

Once stuttering begins in young children, what keeps it going? Four current ideas attempt to explain what perpetuates stuttering: Breakdown Hypotheses, Anticipatory Struggle Hypothesis, Doubt, and the Interaction of Environment and Temperament.

Breakdown Hypotheses

The breakdown hypotheses suggest that, whatever broke down in the first place, remains broken. The brain pathways for talking still involve more of the right side of the brain than is normal, or the auditory feedback system is still amiss.

Anticipatory Struggle Hypothesis

The anticipatory struggle hypothesis suggests that, once children develop the habit of talking in a tense, forceful, and difficult way, they begin to anticipate such difficulty and develop fears around their talking and struggle. The stuttering is maintained by fearfully anticipating such difficulty and trying to avoid it. The anticipatory struggle hypothesis has an element of self-fulfilling prophesy in it: the person expects to have difficulty talking and then does. Once the individual senses that struggle and difficulty are imminent, s/he does things to try to minimize or avoid the difficulty and reduce the fear, such as repeating a word many times until the next word comes out fluently or blinking rapidly in time with the repetition to "help" the word come out. These strategies often make the stuttering more conspicuous and heighten the fear and avoidance. If the person stops being afraid of the stuttering, s/he would not need to avoid it, and would eventually stop stuttering. Some clinical evidence supports this notion. Many people who stutter find that when they stop avoiding their stuttering and begin stuttering openly, their stuttering diminishes in severity and frequency, although it does not go away completely. The notion of stopping the fear and avoidance lies behind the therapy strategy of voluntary stuttering. When people stutters on purpose and with control, they can diminish the fear associated with stuttering.


The notion of doubt provides an interesting and effective way to describe how children who stutter develop a vicious cycle of fear, avoidance, and doubt, which reinforce their original doubt in their abilities to speak and reinforce their stuttering.

A history of difficulty, struggle, negative reactions from others, and frustration at not getting a message out quickly and smoothly, plant the first seeds of doubt in a child's mind. The child doubts her/his ability to talk quickly, smoothly, and easily like everybody else talks. Doubt leads to over regulation as the child tries to control her/his speech muscles to make them work right. Speech is an automatic behavior most of the time and the speech muscles function best without us exerting conscious, direct control over them. When we exert deliberate control over the speech muscles, as with over regulation, we interfere with their normal abilities to function properly.

The over regulation and interference with a normally automatic behavior causes tensing and fragmenting of the behavior. The behaviors are slow, stiff and jerky rather than quick, smooth and fluid. The tensing and fragmenting show up as repetitions and prolongations, the early core behaviors of stuttering. The child does not like the tensing and fragmenting in her/his speech and so tries to avoid them. Children develop different ways to avoid the core behaviors of stuttering. They will use fillers (um, uh), silent pauses, talk around a word they think they may stutter on, or not finish a sentence because they don't want to stutter on a word. When avoidance doesn't work and the child experiences tensing and fragmenting, the child will try to escape the discomfort and the penalty of that situation as quickly as possible. Some escape behaviors include jerking the head, tapping a finger or a foot, and blinking the eyes. Escape devices can be quite powerful to the child who stutters because they relieve some of the physical tension and discomfort that the child experiences during these intense moments of stuttering.

All of these phenomena lead the child back to doubting her/his ability to talk quickly, smoothly, and easily. With renewed doubt in her/his abilities to communicate, the child cycles through the pattern of over regulating, tensing, fragmenting, avoiding, and escaping, again and again.

Interaction of Temperament and Environment

The interaction of temperament and environment are actually pieces of a broader explanation of stuttering referred to as the multifactorial theory. The multifactorial theory suggests that heredity, brain development, personality, learned behavior, and environmental factors all converge to cause and perpetuate stuttering. The elements of temperament and environmental influences fit well with ideas of how stuttering is maintained once it begins.

Long standing clinical evidence suggests that a child's temperament might play a role in the development of stuttering. Many a parent has commented that their child who stutters is more sensitive than their other children; sensitive to change, to other people's reactions, to environmental stressors, and to their own speech mistakes and failures. Research in child development suggests that some children inherit a temperament that makes them react more to unfamiliar, threatening, or challenging situations. These kids may have a lower threshold of tolerance for such things and this lower threshold of tolerance shows up as increased physical tension in the speech muscles when talking in unfamiliar or threatening situations. Children who inherit inefficient neurological circuits (pathways that go into the right side of the brain) and a sensitive temperament may react to their early dysfluencies with increased muscular tension, leading to more dysfluencies, more severe dysfluencies, and more distress.

Environmental factors can contribute to the perpetuation of stuttering in at least two ways. Parents' and family members' reactions to a child's dysfluencies can help or hinder the brains attempts to reorganize the speech pathways. When family members speak at a slower rate, present fewer demands for fluency, and minimize their reactions to stuttering behaviors, these adjustments may give the child's brain a chance reorganize the speech pathways. Likewise, temperament is influenced by interactions with family members. Through interactions with parents, grandparents, siblings, and others, children learn strategies and skills for handling and expressing their emotions. If family members show minimal reaction to a child's stuttering behaviors and encourage the child to accept those moments of disfluency, then the child may learn to minimize her/his own reactions to stuttering.


We are far from solving the mystery of what causes stuttering. We have many pieces of the puzzle available to us right now but may not know what some of those pieces mean. Here is one possible way to organize the pieces thus far. Children may inherit stuttering on one gene and a tendency to persist or recover from stuttering on another gene. One gene may control the organization of pathways in the brain. In the early developmental years, the brain lays down its pathways based on our experiences. If a child misses talking for 7 years, s/he will not have those pathways developed in the brain and will have difficulty learning to talk when older because the brain will be less plastic and have a harder time making new pathways. With stuttering, the child may begin with pathways that use both hemispheres and that aren't very efficient for talking. The child's talking may be full of repetitions, pauses, hesitations, and prolongations as a result of these inefficient pathways.

The tendency to persist in stuttering may be related to temperament and controlled by another gene. Because of a sensitive or reactive temperament, a child might feel more threatened by early dysfluencies and react to them with more tension. Temperament may also be located on the right side of the brain, opening up the potential for the speech pathways and the emotional reaction pathways to intersect and interfere with each other. The repeated experiences of reacting to dysfluencies with increased tension and anxiety may entrench those pathways, making it more difficult for the brain to find an alternate route that is more efficient for talking.


Posted May, 1997
Revised January, 2001

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