Short Description or Definition
A phonological disorder is an inability to articulate speech sounds accurately. The disorder may have a motoric (phonetic) component as well as a linguistic or cognitive (phonemic) basis. Therefore, phonological disorders may affect both the intelligibility of a child’s speech and his or her internalized knowledge of the language’s sound system. The errors committed are usually rule governed, i.e., they show a pattern across all words spoken.
The Diagnostic and Statistical Manual of Mental Disorders Fifth Edition (DSM-5, American Psychiatric Association 2013), specifies four criteria that must be present in order for Speech Sound Disorder (which includes Phonological Disorder) to be diagnosed. First, an individual must exhibit persistent unintelligible speech consisting of phoneme addition, omission, distortion, or substitution, which interferes with verbal communication. Second, the deficits must interfere with social participation, academic performance, and/or occupational performance. Third, the onset of symptoms is in childhood. Fourth, the symptoms cannot be accounted for by another medical or neurological condition.
Phonological disorders are among the most prevalent communication disabilities diagnosed in preschool and school-age children, affecting 10% of this population. Children with phonological disorders are also at risk for reading and writing disabilities. If left unresolved, phonological disorders have long-term consequences that may interfere with an individual’s future social, academic, and vocational well-being, largely resulting from persistent, reduced intelligibility of speech.
For individuals with ASD, impairments of phonological skills may be present, but compared to the difficulties shown in other language domains (social communication, stereotyped lexical usage, etc.), these skills are relatively preserved. Approximately one-third to one-half of individuals with ASD present with significant difficulty using speech as a functional and effective means of communication. In these individuals, it is not uncommon for vocal attempts to be of limited intelligibility due to difficulties producing a variety of consonant sounds and using more complex syllable structures, such as those in multisyllabic words. The nature of these difficulties is not well documented in the literature; however, underlying difficulties may include challenges with oromotor planning and/or delays in phonological development (Lord and Paul 1997; National Research Council 2001). An estimated one-fourth of children with ASD are nonverbal, i.e., they lack spoken language. Most children with ASD who speak begin to do so by age 7 and almost never after age 13 (Pickett et al. 2009).
Among speaking children with ASD, there is typically no specific developmental impairment at the level of segmental phonology (consonant and vowel production). The speech that they produce will generally be understood, though, as with all children, it will undergo a process of developmental change to become more and more adultlike. Although unintelligible speech is not a core feature, atypical cases have been reported in the literature of children with ASD who exhibit severe phonological difficulties (e.g., Wolk and Giesen 2000). Moreover, there is evidence that distortion errors – which represent a phonetic rather than phonemic disorder – may persist into adulthood (Shriberg et al. 2001). Perception of speech sounds appears to be different in individuals with ASD. Functional imaging studies have indicated that both children and adults with autism show deficits in speech-sound processing (Boddaert et al. 2004). This impairment is limited to speech sounds; it does not affect the perception of tones (Whitehouse and Bishop 2008). The relationship between these deficits and the speech production abilities of individuals with ASD is not yet known.
Natural History, Prognostic Factors, and Outcomes
The development of speech begins at birth. As the speech mechanism systems of breathing, voice, and articulation mature, an infant is able to make a controlled sound. This begins with soft, repetitive “cooing” vocalizations and by 6–7 months has progressed to repetitive syllables such as “ba, ba, ba” or “da, da, da.” This babbling becomes more elaborated and melodic so that it often has the tone and cadence of adult speech but does not contain real words. By the end of their first year, most children are starting to say a few simple words.
During the second year of life, children slowly develop a single-word vocabulary and by the end of that year most are putting words together. During the period of single-word speech, it is believed that children learn the sound structure of words as wholes. After the point where they have learned around 50 words, they begin to show awareness of the individual sounds or phonemes in words. The errors they commit start to show regularity, so that the same mistakes are committed on the same phonemes in different words (e.g., /s/ will be replaced by /t/ in the words sun, see, sick, etc.).
During the remainder of the preschool years and, for some children, extending into the early school years, there is a gradual process of phonological learning that can be described from two perspectives, one of sound mastery and the other of error suppression. In the first perspective, children are seen to slowly master all the vowels, individual consonants, and consonant sequences of their native language. Certain classes of sounds are mastered earlier than others. For example, many early emerging sounds are made in the front of the mouth by blocking the flow of air or directing it into the nasal cavity: /p, b, t, d, m, n/. Later emerging sounds are either made in the back of the mouth (e.g., /k, g/) or by partially blocking airflow to create fricative sounds (e.g., /s, z, th, sh/). In the second perspective on phonological development, children are observed to show regular ways of simplifying their pronunciations compared to those of adults. These patterns, or phonological processes, include changes to the syllable structure of words (e.g., omitting unstressed syllables or eliminating one of the sounds in a consonant sequence), omissions of sounds (especially at the ends of syllables), and substitutions of earlier/simpler sounds for later/more complex ones (e.g., substituting /t/ for /k/). Many phonological processes occur commonly in children and are considered to be part of their biological predisposition; these are referred to as “natural” processes. Others may be idiosyncratic or unique to an individual child.
Phonological disorders in children are characterized by speech that is difficult to understand, especially by individuals who do not know the child speaker well. As a rule of thumb, children should be understood by strangers about half the time at age 2, about 75% of the time at age 3, and nearly all the time at age 4. When speech is unintelligible, it is usually due to a combination of common and uncommon errors. Certain of the normal or “natural” phonological processes may persist beyond the ages at which they are normally suppressed. Other atypical or idiosyncratic processes may also be present. There may also be a combination of phonemic (substitution, omission, and addition of sounds) and phonetic (distortions of sounds) errors together in the same child. Individuals with ASD may present unintelligible speech for all these reasons and, in addition, may exhibit disturbances of prosody that further compromise their intelligibility.
Clinical Expression and Pathophysiology
Phonological disorder is an impairment in the ability to comprehend or produce the sound system of a language. This sound system is characterized as having two parts: segmental phonology, which pertains to consonants and vowels and their combination into syllables, and nonsegmental phonology (also called suprasegmental phonology or prosody), which includes speech variables such as rate, stress, intonation, and pause. In the field of speech-language pathology, the term phonological disorder is typically used to refer to segmental problems, specifically difficulty in inducing the rules that govern sound combinations. Thus, a phonological disorder is viewed as a subtype of language disorder (Bauman-Waengler 2012).
With such disorders, errors are observed in the production of individual speech sounds and in the formation of syllable structures of words. Sounds may be omitted, substituted by other sounds, or added to the normal form of a word. When these errors are numerous or result in sounds quite different from the targets, they may produce speech that is partially to fully unintelligible to a listener, especially one who is unfamiliar with the speaker. Phonological disorders are distinguished from phonetic disorders (also described as articulation disorders) that result from slight misalignments of the articulators during speaking and are manifested as distortion errors. Unlike phonetic disorders, phonological disorders are frequently part of a larger language disorder characterized by impairments of one or more other linguistic domains such as vocabulary, comprehension, morphosyntax, or literacy.
Although nonsegmental phonological or prosodic impairments are normally not considered part of a phonological disorder from a clinical perspective, they clearly belong within the linguistic domain of phonology. Moreover, unusual prosodic features are a concomitant behavior in many individuals with autism. It is one of a number of behavioral red flags that distinguish toddlers with autism from those either developing normally or with other types of developmental delay (McCann and Peppe 2003; Wetherby et al. 2004). Among the speech production behaviors where differences are reported to exist are stress, rate, chunking (verbal phrasing), intonation, and expression of affect. Problems have also been noted in the detection and comprehension of prosodic variation in speech. In spite of this, accounts of prosodic disability in autism are inconsistent and have utilized widely varying populations and methodologies.
Evaluation and Differential Diagnosis
Phonological disorders in young children are assessed through standardized and nonstandardized procedures. Optimally, two speech samples are obtained: one of single-word speech, typically elicited through a picture- or object-naming task, and the second of connected speech, gathered through a play interaction or short interview. To elicit the first type of sample, a large number of standardized, norm-referenced tests of speech-sound production are available for children 3 years or older (e.g., Clinical Assessment of Articulation and Phonology, Second Edition, Secord and Donohue, 2013; Goldman-Fristoe Test of Articulation-Third Edition, Goldman and Fristoe 2015; Arizona Articulation Proficiency Scale, Third Edition, Fudala 2000).
Speech samples of both types are transcribed phonetically and then analyzed to determine whether the child displays primarily speech production deficits (phonetic errors or sound distortions) and/or deficits associated with phonological constraints (phonemic errors of omission, substitution, or addition of sounds). Independent analyses such as a phonetic inventory (listing of all sounds produced, regardless of correctness) are used to evaluate possible sensory or motor limitations. The child is also screened for auditory acuity and is given an oral-peripheral examination to determine whether there exist structural or physiological limitations to speech. Relational analyses such as an assessment of phonological processes (patterns of sound simplification, such as replacing posterior /k, g/ sounds with anterior /t, d/ sounds) are used to determine whether errors are developmentally common or idiosyncratic. The identification of error patterns also forms the basis for treatment to improve speech intelligibility.
In the treatment of phonological disorders, the primary goal is to improve a child’s speech intelligibility to facilitate effective communication. This entails both teaching the accurate production of speech sounds and improving the conceptual organization of speech-sound information so that phonemic contrasts are clearly marked. Effective and efficient treatment relies on a generalization of learning. The goal is to induce a widespread change in a child’s sound system so that it is more in line with the phonology of the target language.
Treatment often occurs in the context of an interdisciplinary service delivery team that may include speech-language pathologists, audiologists, nurses and physicians, occupational and physical therapists, parents, psychologists, social workers, special educators, and teachers. The composition of this team is dependent on the child’s needs not only in the area of communication but in development generally. The team initiates and coordinates the optimal intervention program for the child and facilitates the program’s transfer and utility in daily settings.
After assessing the phonological disorder and identifying and prioritizing the errors that exist, a treatment plan is developed to correct speech-sound production. The goal of treatment is to improve accuracy and use of speech sounds so that intelligibility is improved in both single words and connected speech. Generalization is sought across all settings in which children communicate. No single treatment approach is used. In general, all approaches utilize structured sound production practice at gradually increasing levels of difficulty.
Intervention for individuals with ASD must often be adapted to suit their unique interests, styles of interaction, and sensory preferences and aversions. For example, the commonly used technique of saturating the child with auditory models of a target speech sound might prove disastrous with an individual who is auditorily hypersensitive. Another common technique, contrasting minimal word pairs such as “call” and “tall,” may be difficult to implement because it relies on role reversal, the teacher playing the student, and vice versa.
References and Reading
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