Table 2.
Proposed consensus-based definitions for vocal biomarker levels 1–4 (VOCAL initiative)
| Term | Definition | Examples | Illustrations |
|---|---|---|---|
| CRA biomarkers (level 1) | CRA biomarkers relate to acoustic signals pertaining to respiration and cardiac function. They represent the earliest stage in the speech production pathway and reflect physiological processes that influence vocalization | Breathing sounds, cough acoustics, and pauses caused by breath support | A cough with low intensity may reflect reduced respiratory drive or weakened supportive muscles. Acoustic analysis of coughs or breathing may indicate respiratory illness or muscular disorders. Frequent pauses in speech may reflect dyspnea or reduced breath control |
| Voice biomarkers (level 2) | Voice biomarkers relate to features from the source of phonation: the lungs pushing air through the vocal folds, which vibrate to generate sound, later shaped by the vocal tract (throat, mouth, nose) | HNR, CPP, fundamental frequency (F0) | In laryngitis, vocal fold inflammation can cause a rough or hoarse voice quality, measurable using CPP. Parkinson’s disease can affect prosody, leading to monotonous speech with reduced pitch variability (F0 range) and inflection |
| Speech/articulatory biomarkers (level 3) | Speech/articulatory biomarkers relate to articulatory processes and speech motor control. They reflect the coordination and functioning of articulators (tongue, lips, soft palate, etc.), which are regulated by neurological control | Articulation rate, speech rate, syllable precision, consonant clarity | In ALS, tongue weakness may impair the articulation of syllables like “Ka” or “Ga.” Variations in rhythm and timing can indicate altered motor coordination or speech effort |
| Cognitive/language biomarkers (level 4) | Cognitive/language biomarkers relate to the content and meaning of speech, reflecting higher-level cognitive functions, language processing, and emotional or social communication cues | Linguistic biomarkers refer to the content of our speech, our lexical access, the words we choose in a sentence, and how we pair words together to form sentences. They can also include syntax, grammar, semantics, and vocabulary concepts. Paralinguistic biomarkers include non-verbal communication elements, such as conveying emotion, cultural cues, and dialects | Linguistic illustration: reduced vocabulary diversity in Alzheimer’s disease or syntactic simplification in aphasia; paralinguistic illustration: intonation patterns signaling questions or emotional states (e.g., rising pitch) may reflect cognitive or affective modulation in conditions like autism spectrum disorder |