Background
Speech contains neuromuscular, physiological, and cognitive components and so is a potential biomarker of mental disorders. Previous studies have indicated that speaking rate and pausing are associated with major depressive disorder (MDD). However, results are inclusive as many studies are small and underpowered and do not focus on clinical samples. These studies have also been unilingual and use speech collected in highly controlled settings. If speech markers are to help understand the onset and progress of MDD, we need to uncover markers that are robust to language and establish the strength of associations in real-world data.
Methods
We collected speech data in 585 participants with a history of MDD in the United Kingdom, Spain, and Netherlands as part of the RADAR-MDD study. Participants recorded their speech via smartphones every two weeks for 18 months. Linear mixed models were used to identify key cross-language markers of depression from a set of 28 speech features.
Findings:
Increased depressive symptoms were associated with speech rate, articulation rate and intensity of speech elicited from a scripted speech task. These three features had consistently stronger effect sizes than pauses.
Interpretation:
Participants with more severe depressive symptoms spoke more slowly and quietly, regardless of the language used. As decreases in speech rate and articulation rate had stronger effects than any of the pausing measures tested, we speculate the observed slowing of speech is most likely due to psychomotor impairments affecting articulation rates.