Speech and Language Development in People Who Stutter

The scientific literature contains many studies demonstrating that children and adults who stutter show somewhat lower scores on intelligence measures in both verbal and non-verbal tasks compared to the general population (Andrews et al., 1983; Paden et al., 1999).

However, these findings should be interpreted with caution. It must be taken into account that throughout their years of schooling and other education, our patients experience significant difficulty expressing their own thoughts. As a result of the secondary fear of public speaking that develops over time, they avoid speaking up and answering teachers' questions. When they do respond, their attention is directed not toward the content of their answer but toward minimizing the visible manifestations of stuttering through various strategies. The criteria used to draw conclusions about intelligence do not account for the specific nature of speech and the linguistic processes of people who stutter.

Linguistic deficit. Stuttering typically begins in early preschool age and inevitably affects subsequent speech development. Comparisons of fluent and stuttering preschool children have revealed that the latter show delays in the development of receptive vocabulary and expressive language. Several researchers have found that the semantic and syntactic planning system in children who stutter is insufficiently developed. In addition, children who stutter make significantly more grammatical errors in conversational speech and, in general, produce simpler and less mature language.

We studied the linguistic abilities of typically developing preschool children and their stuttering peers. Test results showed that preschool children who stutter do not differ from their peers in speech comprehension. They correctly follow the logic of a narrative and do not make errors in understanding cause-and-effect relationships. Despite the absence of cognitive impairments, children who stutter demonstrated significant delays compared to their typically developing peers in the structuring of spoken utterances, word agreement within sentences, syntactic and grammatical skills, active vocabulary size, and speed of utterance construction. Difficulties in forming a spoken utterance may reflect challenges in evaluating, organizing, and planning material for linguistic output. It is clear that children who stutter have difficulty with the process of morphosyntactic construction, which in turn delays sentence formulation.

Beginning in childhood, stuttering leaves a specific imprint on the acquisition of complex linguistic skills. From an early age, the speech activity of a person who stutters is directed simultaneously toward constructing a grammatically correct and coherent utterance and toward eliminating the impact of involuntary muscle spasms on expressive speech.

Adults who stutter report that from childhood they have monitored their speech in order to conceal the manifestations of the disorder and to try to prevent occurring blocks through various strategies and tricks. The most common speech strategies include: substituting words to avoid particular problematic sounds; making periodic pauses within and between words to exclude the influence of involuntary contractions of the articulatory, vocal, and pharyngeal muscles on speech; frequently inserting habitual, easy filler words that carry no semantic meaning before difficult words ("well," "uh," "you know," etc.). Without interrupting the flow of speech, the person who stutters must pre-analyze the planned utterance, either preceding difficult words with filler words or replacing them with synonyms, and pausing during involuntary muscle contractions to prevent their impact on speech.

Thus, the linguistic activity of a person who stutters is directed from childhood not so much toward constructing a grammatically correct and elaborated utterance that most accurately reflects their thoughts and feelings, but rather toward minimizing the visible manifestations of the disorder. The linguistic processes of a person who stutters must be directed simultaneously toward forming the upcoming utterance and toward scanning the upcoming sentence. The primary task of the person who stutters is not to construct a correct utterance but to navigate between involuntary muscle contractions and to overcome motor difficulties. The execution of this complex cognitive-linguistic task of dual speech monitoring appears to be supported by the involvement of right-hemisphere homologues of the brain structures that participate in normal linguistic activity.

In recent years, positron emission tomography and magnetic resonance imaging have opened new possibilities for studying the morphofunctional substrate of speech, both in typical speakers and in people who stutter. These studies have refined existing understanding of the localization of sensorimotor and cognitive-linguistic components of speech. It has emerged that the cerebral organization of the linguistic components of speech in adults who stutter is fundamentally different from the norm. In typical speakers, cerebral blood flow during speech formulation increases primarily in the left hemisphere. In people who stutter, the increase in blood flow is absent, spatially restricted, bilateral, or lateralized to the right hemisphere.

Analysis of existing PET and MRI data leads to the understanding that people who stutter, during the execution of linguistic activity, show reduced activation of the same left-hemisphere structures as fluent speakers, but additionally recruit the right-hemisphere homologues of those structures during speech. The fact that left-hemisphere sensory and associative areas are more activated in fluent speakers during speech, while right-hemisphere subcortical and frontal areas are more active in people who stutter, indicates that stuttering involves the additional and predominant recruitment of right-hemisphere speech area homologues. This allows people who stutter to exercise dual monitoring over their speech.

The speech activity of a person who stutters is directed from childhood primarily toward the stuttering-specific processes of monitoring, planning, and restructuring their own speech in order to avoid the manifestations of stuttering and to conceal their disorder. The atypical pattern of lateralization of linguistic processes may be the result of an individually adapted system that develops from childhood and early adolescence in attempts to speak fluently. The development of proper speech skills is thereby delayed, since the right hemisphere's speech areas — which are not adapted for semantic-syntactic processing and the preparation of linguistic output — become part of the neural substrate for the development of linguistic abilities.

In summary, a child or adult who stutters does not differ in intellectual level from other people, but in most cases demonstrates reduced linguistic skills.