Diadochokinetic (DDK) rate is a test used by speech-language pathologists (SLP) to assess, diagnose, and treat speech malfunctions. It is also known as the Fletcher Time-by-Count Test of Diadochokinetic Syllable Rate.
DDK rate measures how quickly a person can accurately repeat a series of rapid, alternating phonetic sounds. These sounds, called tokens, are designed to test different parts of the mouth, tongue, and soft palate in the back of the throat. The tokens contain one, two, or three syllables. For example, “puh,” or “puh-tuh,” or “puh-tuh-kuh.”
The speech exercises may test articulation, intelligibility, perception, respiration, voice quality, nasality, loud/soft tones, and swallowing.
DDK rate determines if there are problems in the speech mechanisms that control motor skills or speech planning functions in the brain. Mechanisms that affect speech include the cerebellum (left side of the brain) and the central nervous system (CNS). They also include the muscle and bone structures in the face, mouth, and throat.
The DDK rate measures repetitions of sounds within a designated amount of time. For example, the results of the test will show how many seconds it takes the patient to repeat a token 10 times.
There are established DDK-rate norms for each year of age through childhood. There are also norms for adults with various underlying conditions. An index of comparative norms has been perfected by clinical trials since the DDK rate was introduced in 1972. The process of perfecting the index continues today.
The data collected by DDK rate is often used together with other diagnostic tests. Together, they determine the underlying causes of speech dysfunction.
DDK rate is used to diagnose adults and children who exhibit limited oral motor, cognitive-linguistic, swallowing, speech, or language skills. The test can determine the severity of speech problems, underlying causes, and courses of treatment.
Underlying conditions affecting speech can include:
- neurological events, such stroke or brain injury
- neurological diseases, such as cerebral palsy or muscular dystrophy
- head/neck or mouth cancer, and impairments after surgery
- birth defects, such as cleft palate
The test can detect specific variations associated with underlying causes. Common variations and associated disorders include:
- Ataxia: a voluntary movement disorder. It involves poor muscle coordination in speaking and swallowing. It is caused by damage to the cerebellum, or a defective gene.
- Dysarthia: a motor speech disorder. It causes slow or limited movement of the mouth, face, and respiratory system. It is often a result of stroke or other brain injury.
- Childhood apraxia of speech: an uncommon speech disorder in which the brain struggles to plan speech and control the mouth muscles.
- Aphasia: a disorder marked by speaking in short phrases that make sense but are produced with great effort. It is caused by damage to the left hemisphere of the brain.
- Oropharyngeal disorders: These cause difficulties in swallowing. They usually result from damage to mechanisms in the throat, such as throat cancer and subsequent surgery.
Measuring DDK rate is usually done in a single session of about 30 minutes. The speech-language pathologist administers the DDK rate and scores the results. The test is carefully timed.
Before the test begins, the SLP demonstrates the token sounds. Patients can then practice making the sounds several times.
A series of tests are performed. Each require the patient to produce a different sound or combination of sounds. For example, the patient may be asked to say the “a” sound 20 times very quickly. They may then be asked to repeat the sound starting at a whisper and getting louder.
Other oral mechanism tests may be used. These include:
- singing to test perceptual ability
- blowing through a straw submerged in water to test breathing and control
If the patient is a child, or a person with brain damage, familiar words like “pattycake” or “buttercup” may be used in place of nonsense syllables.
The results of the test will be compared to standard normalcy measurements. This is done using the DDK rate system. For example, a typical 10-year-old child produces 20 repetitions of the syllable “puh” in 3.7 seconds. Any variance in pattern or production of sound will be measured and used to assess a patient’s condition.
Exercises used in DKK rate may also be used in therapy to help a patient improve their speaking skills.