3.1 Speech
3.1.1 What is Speech?
Speech refers to the fluent and precise coordination of the tongue, teeth, lips, palate, jaw, voice and respiratory system to create the sounds of our language. Or more simply, it’s the way that we make and use sounds to create words.
Speech is a highly complex process. To send a verbal message that another person can understand, we must first create a mental representation of the words we want to say. We do this by selecting the phonemes required and organising them into the correct sequence (e.g., /k/ /a/ /t/). The brain then creates a motor plan that is sent to the muscles required for speech production. Finally, the plan is executed by the articulators to produce the word (e.g. cat). A breakdown at any of these levels can result in speech sound errors which can make speech difficult to understand and cause frustration for the speaker (Bowen, 2023).
3.1.2 What is a speech sound disorder?
Speech sound disorder is an umbrella term used to describe difficulties with either creating or correctly using sounds and syllables within words to produce clear speech (ASHA, 2025a). Speech sound disorders can be present from birth, as is the case with developmental speech sound disorders, or be acquired as a result of a sensory-perceptual difference (e.g., hearing loss), structural differences (e.g., cleft lip), or neurological injury and/or illness (e.g., stroke, a traumatic brain injury, Parkinson’s disease). Speech pathologists are the only professionals who can diagnose and treat speech sound disorders.
3.1.3 Developmental speech disorders
Developmental speech sound disorders are speech difficulties that have no known cause and are present from birth. In this section, we will explore the 3 main types of developmental speech disorders:
- Articulation disorders
- Phonological disorders
- Childhood Apraxia of Speech
Articulation Disorders
A person with an articulation disorder has difficulty physically producing individual speech sounds using the lips, teeth, tongue, palate, voice and respiration (Bowen, 2023). They may distort sounds, as is the case with a lisp, or they might replace sounds they cannot make with ones they can make (e.g., a person who can’t say /r/ might say wabbit instead of rabbit). Articulation disorders are considered to occur at the phonetic level, as the difficulty is with coordinating the motor movement required to make the sound.
Some sounds are more difficult to make than others. When children are younger, they will often use easier sounds in place of more difficult sounds. As they gain more coordination over their articulators, they will begin to use the correct sounds. Age of acquisition refers to the ages at which children should be able to produce and use each sound correctly. If a child is unable to produce a sound correctly after the sound’s age of acquisition, they are considered to have an articulation disorder.
The Learning English Consonants chart is a useful resource that summaries the age of acquisition for English consonants.
The video below is an example of a child with an articulation disorder.
Phonological Disorders
A phonological disorder is a condition where a person has difficulties using speech sounds where they need to in words, despite the fact that they know how to produce the sounds correctly (Bowen, 2023). It is a difficulty related to understanding the rules and sound patterns of their language.
Remember our discussion of place, manner and voice in Chapter 2.2? For some children, they have difficulty tuning in to these differences between sounds. For example, the sounds /b/ and /p/ are very similar. They have the same place (they are both made with the lips) and they have the same manner (they are both short, explosive sounds). The feature that makes them different is the voicing: when we say /b/ our voice is turned on, when we say /p/ our voice is turned off. If a child has not yet worked out that in English turning your voice on and off is meaningful (i.e. it can change the meaning of a word) they might consider /b/ and /p/ to be the same and use them interchangeably while talking. In fact, they might do this with lots of sound pairs that only differ in voicing (e.g. /t/ and /d/, /k/ and /g/, /f/ and /v/ etc). This is referred to as a phonological error pattern or phonological process. That is, the child can make physically make the sounds but does not use them when they should because they do not understand the meaningful sound contrasts in the English language (Bowen, 2023).
Phonological speech errors are a typical part of development. As children develop a clearer understanding of how sounds and words are organised and structured in English, these error patterns are expected to resolve. ‘Age of elimination’ refers to the age by which each individual phonological error pattern should have naturally faded away (Bowen, 2023). If an error persists past this age, the child is considered to have a phonological speech sound delay. Some children present with unusual phonological speech patterns that are not a typical part of development. Children who exhibit these atypical phonological processes are considered to have a phonological speech sound disorder. Atypical patterns are highly unlikely to resolve without targeted speech pathology intervention.
Developmental Phonological Processes (ASHA, 2025b)
| Phonological Process | Description | Example | Age of Elimination |
| Assimilation | When one sound becomes the same or similar to another in a word. | elephant –> efefant | 3 years |
| Fronting | When a sound made at the back of the mouth is substituted with a sound made at the front of the mouth. | cup –> tup | 4 years |
| Stopping | When a fricative (long sound) or an affricate is substituted with a stop (short sound). | zoo –> doo | /f/, /s/ – 3 years
/z/, /v/ – 4 years /sh/, /ch/, /dz/, /th/ – 5 years |
| Gliding | When a glide (/r/ or /l/) is substituted with a liquid (/w/ or /j/). | rabbit –> wabbit
lick –> yick |
6-7 years |
| Deaffrication | When an affricate (/ch/ or /dz/) is substituted with a fricative (long sound). | cheep –> sheep | 4 years |
| Cluster Reduction | When a consonant cluster is reduced to a single consonant sound. | spider –> pider
flying –> lying |
with /s/ – 5 years
without /s/ – 4 years |
| Weak Syllable Deletion | When an unstressed or weak syllable within a word is omitted. | tomato –> mato | 4 years |
| Final Consonant Deletion | When the final consonant in a word is omitted. | been –> bee | 3 years |
Atypical Phonological Processes (ASHA, 2025b)
| Phonological Process | Description | Example |
| Backing | When front sounds are substituted with back sounds. | tip –> kip |
| Initial Consonant Deletion | When the first consonant in a word is omitted. | pool –> ool |
| Medial Consonant Deletion | When consonants in the middle of words are omitted. | ladder –> la_er |
| Sound Preference (aka. phoneme collapse) | When many speech sounds are substituted with a favoured sound. | spill –> dill
reef –> deef lake –> dake car –> dar |
| Glottal Replacement | When a sound is substituted with a glottal stop. | sat –> saʔ |
| Vowel Errors | When a vowel substituted for another vowel. | purple –> parple |
As phonological disorders are language-based speech sound disorders, children with this diagnosis have a higher risk of also experiencing language and literacy difficulties compared to their peers. Early intervention is therefore critical to ensure children have the strongest possible start to their schooling.
Below is a short video of a child with a phonological disorder. Can you work out which phonological processes he has?
Phonological Processes by Blake Self
Consistent vs Inconsistent Phonological Disorders
Most children present with consistent phonological disorders, meaning that they will use the same errors patterns every time they say a word. For example, if a child with the phonological process voicing was asked to say ‘pet’ three times, they would say ‘bet’ each time. Children with inconsistent phonological disorders, however, will produce words with different errors each time they say them (Dodd et al., 2024). For example, if asked to say ‘pet’ three times they might say ‘bet’, ‘get’ and ‘et.’ Children with inconsistent phonological disorders are often much more difficult to understand during conversation and require specific intervention targeted at improving speech consistency prior to moving to more classic phonological approaches.
CHILDHOOD APRAXIA OF SPEECH
Childhood Apraxia of Speech (CAS) is a neurodevelopmental disorder that causes difficulties with the programming and planning of the motor movements required for clear speech. People with CAS know what they want to say, but when they go to speak their speech sounds are often jumbled and the way they say words inconsistent. CAS is less common than articulation or phonological speech sound disorders, affecting approximately 1 in 1000 children (McCabe et al., 2024). While many people with CAS do not know the reason for their speech disorders, approximately 33% of cases are due to an underlying genetic difference, such as chromosomal duplication or deletion (McCabe et al., 2024).
To be diagnosed with CAS, a child’s speech must meet the following diagnostic criteria:
- Inconsistent production of consonants and vowels when repeating syllables and words.
- Lengthened and disrupted coarticulatory transitions between sounds and syllables
- Inappropriate prosody, including use of unusual stress patterns across words and phrases.
CAS is a lifelong condition but with early intervention speech intelligibility can improve significantly.
Watch this video of child with CAS. Can you understand what she is saying?
Childhood apraxia of speech 3 year old girl by UrbanKowboy
3.1.4 Acquired speech disorders
Previously in this section you have learned about the practice area of ‘speech’ including aspects related to developmental speech disorders. Now we will explore acquired speech disorders. Acquired motor speech disorders are speech impairments that a child or an adult may develop after birth, typically due to injury, illness, or disease.
Common causes of acquired motor speech disorders include:
- Brain injury: Trauma to the brain (e.g. stroke; traumatic brain injury) can impact areas of the brain and nervous system responsible for motor planning and execution of speech.
- Neurological conditions: Neurological conditions such as Parkinson’s disease, multiple sclerosis, dementia or Motor Neuron Disease can affect speech.
- Infections: Illnesses like meningitis or encephalitis that affect the brain may lead to speech issues.
- Tumors: Head and/or neck tumors and cancer interfere with speech.
- Surgical trauma: Surgery involving the head, neck, or brain may result in speech difficulties.
Two main types of acquired motor speech disorders include acquired apraxia of speech and dysarthria.
Acquired apraxia of speech (AOS)
Acquired apraxia of speech (AOS) (also referred to as verbal apraxia or dyspraxia) is a motor speech disorder that occurs when there is damage to the areas of the brain responsible for planning, sequencing, and coordinating the movements needed for speech.
Key features of acquired apraxia of speech include:
- Speech sound errors: People with AOS may make different speech errors each time they try to say the same word (i.e. inconsistent speech sound errors) with speech errors commonly characterised by phoneme additions, omissions and/or distortions.
- Slow rate of speech/segmented speech: There may be noticeable difficulties initiating speech, as well as pauses or disruptions in speech, including lengthened and equal stress of syllable segments, and slow rate of speech. (Duffy, 2020)
The video below provides a further summary about the key features of apraxia of speech.
What is apraxia of speech? by Expressable Speech Therapy
Dysarthria
Dysarthria is a group of motor speech disorders that affects the muscles used for the motor execution aspects of speech production. This may be due to problems associated with the muscles required for speech movement related to the speech subsystems of respiration, phonation, articulation and resonance. These problems may include muscle weakness, reduced range and strength of movement, increased/decreased muscle tone, problems with coordination. This can affect the person’s ability to articulate speech sounds and words clearly; and problems with voice quality, speech loudness, and speech rate. Unlike apraxia of speech, where the issue is with planning and sequencing movements, dysarthria is caused by problems with the muscles themselves or the neurological control of those muscles.
Speech characteristics associated with dysarthria can include:
- Slurred or mumbled speech
- Slow or rapid speech rate
- Weak voice or a breathy, harsh, or nasal tone
- Difficulty pronouncing words clearly
There are different types of dysarthria, depending on which part of the brain and nervous system is affected. Some people may present with mixed dysarthria which may be one or more of the dysarthria types outlined below. Examples of the different dysarthria types include:
| Dysarthria type | Nervous system components affected and example aetiologies | Affects on muscle movement | Speech Characteristics |
| Spastic dysarthria | Bilateral damage to the upper motor neurons (UMNs) of the pyramidal (direct) and extrapyramidal (indirect) pathways (e.g. stroke). | Spasticity, weakness, reduced range of motion, and slow speech movements. | Strained-strangled voice quality, slow rate, imprecise articulation, monopitch, and reduced stress. |
| Flaccid dysarthria | Damage to the lower motor neurons (LMNs), which include the cranial nerves (CNs) involved in speech production, the neuromuscular junction, or the muscles themselves (e.g. brain stem stroke; myasthenia gravis). | Weakness, hypotonia, reduced reflexes, and atrophy. | Breathy voice quality, hypernasality, and imprecise consonants. |
| Hypokinetic dysarthria | Damage to the basal ganglia control circuit, particularly affecting the substantia nigra and its dopamine pathways (e.g. Parkinson’s Disease). | Rigidity, reduced range of motion, and difficulty initiating movements. | Vocal tremor, monopitch, reduced loudness, short rushes of speech, and imprecise articulation. |
| Hyperkinetic dysarthria | Damage to the basal ganglia control circuit, particularly dysfunction in the inhibitory pathways (e.g. Huntington’s Disease). | Involuntary movements (hyperkinesia) that interfere with speech production. The movements can be slow (dystonia) or rapid (chorea, myoclonus, tremor, tics). | Irregular articulatory breakdowns, loudness variations, stress variations, voice stoppages or strained-strangled voice quality, intermittent hypernasality. |
| Ataxic dysarthria | Damage to the cerebellum or its connections (Friedreich’s ataxia). | Incoordination, impaired timing, and reduced accuracy of speech movements. | Slurred and imprecise speech, irregular articulatory breakdowns, variable stress patterns, and slow speech rate. |
| Unilateral upper motor neuron dysarthria | Unilateral damage to the upper motor neurons (UMNs) affecting the corticobulbar pathways that control speech muscles. As most cranial nerves receive bilateral innervation (except for the lower face and tongue), speech deficits are usually milder compared to other dysarthrias (e.g. unilateral stroke). | Unilateral facial weakness. | Imprecise consonants (mild articulatory breakdowns), slow rate and mild harsh voice quality, reduced loudness and occasional hoarseness. |
(Duffy, 2020)
The video below provides a good summary of dysarthria.
South TEES NHS – What is dysarthria and how can you help? by Ward 26
Speech refers to the fluent and precise coordination of the tongue, teeth, lips, palate, jaw, voice and respiratory system to create the sounds of our language. Or more simply, it’s the way that we make and use sounds to create words.
Speech sound disorder is an umbrella term used to describe difficulties with either creating or correctly using sounds and syllables within words to produce clear speech.
A person with an articulation disorder has difficulty physically producing individual speech sounds using the lips, teether, tongue, palate, voice and respiration.
A phonological disorder is a condition where a person has difficulties using speech sounds where they need to in words, despite the fact that they know how to produce the sounds correctly. It is a difficulty related to understanding the rules and sound patterns of their language.
Childhood Apraxia of Speech (CAS) is a neurodevelopmental disorder that causes difficulties with the programming and planning of the motor movements required for clear speech.
Acquired apraxia of speech (AOS) (also referred to as verbal apraxia or dyspraxia) is a motor speech disorder that occurs when there is damage to the areas of the brain responsible for planning, sequencing, and coordinating the movements needed for speech.
Dysarthria is a group of motor speech disorders that affects the muscles used for the motor execution aspects of speech production.
