Question
What is intelligibility as it relates to dysarthria?
Answer
Dysarthria is not a single speech disorder but rather a group of motor speech disorders characterized by abnormalities in the movements required for speech production. These abnormalities can affect the strength or speed of the movements, the range of motion, or the tone and accuracy of those movements. Any of these aspects can be impacted in individuals with dysarthria.
Sometimes we refer to "the dysarthrias" in the plural, as the term encompasses various subtypes of dysarthria, each defined by distinct perceptual characteristics and the underlying etiology of the disorder. Some of those different types are:
- Flaccid
- Spastic
- Ataxic
- Unilateral upper motor neuron
- Hypokinetic
- Hyperkinetic
- Mixed
- Undetermined
When we talk about intelligibility, we're referring to the degree to which a listener understands the speaker's message. I don’t mean understanding in an empathetic or emotional sense, but rather the literal decoding of the words that the speaker is producing. Intelligibility is inherently a perceptual outcome, meaning we're capturing the listener’s perception of what the speaker says.
The outcome of intelligibility can be influenced by factors like acoustics, muscle activity, and other physical aspects, but ultimately, intelligibility is a perceptual outcome. It’s reduced when the listener cannot effectively decode the speech. Intelligibility is a core functional deficit in dysarthria, making it a crucial measure that is frequently tracked in both clinical practice and research. However, as I mentioned earlier, changes in intelligibility occur across all dysarthria subtypes. Therefore, it does not specifically predict the subtype, etiology, or which speech subsystems might be impaired.
This Ask the Expert is an edited excerpt from the course Dysarthria: Best Practices for Assessing Intelligibility, presented by Kimberly Dahl, MS, CCC-SLP.
