Abstract
Background: Prosody refers to nonverbal speech features including pitch, intonation, stress, duration and intensity. These features are critical for successful communication, conveying emotions and distinguishing sentence structures. Previous research suggests that emotional prosody perception is impaired in neurodegenerative diseases like Alzheimer’s disease (AD) and primary progressive aphasia (PPA). However, no previous research has investigated how emotional prosody perception is affected in these patient groups under non-ideal listening conditions such as those encountered in everyday listening. Here, we aimed to examine the perception of emotional prosody in patients with AD and PPA syndromes under both clear and degraded (noise-vocoded) speech conditions.
Methods: We recruited 18 patients with AD, nine with logopenic variant PPA (lvPPA), 11 with non-fluent/agrammatic variant PPA (nfvPPA), and 11 with semantic variant PPA (svPPA), along with 24 healthy controls. Participants listened to numerical speech stimuli portraying three emotions (anger, surprise, sadness) in clear and noise-vocoded forms, and for each speech token were asked to identify the emotion being conveyed. We noise-vocoded the stimuli at three levels to generate easy, medium, and hard listening conditions. Performance was correlated with questionnaire measures of socio-emotional functioning.
Results: All patient groups showed significant impairments in identifying clear emotional prosody compared to healthy controls. These deficits were exacerbated under noise-vocoded speech conditions, with all patient groups performing significantly worse than healthy controls and patients with lvPPA performing significantly worse than those with svPPA. There was no interaction between level of noise-vocoding and participant group, but across groups, participants performed more poorly with more degradation. Significant correlations were observed both for clear and noise-vocoded emotional prosody identification with social cognition measures; however, these correlations were seen more consistently for performance on noise-vocoded emotional prosody than clear speech.
Conclusion: Our findings suggest that emotional prosody identification is impaired in AD and PPA patients, and that these deficits are particularly prominent under non-ideal (noise-vocoded) listening conditions. These findings open a window on a dimension of real-world emotional communication that has often been overlooked in dementia, with particular relevance to social cognition, and begin to suggest a novel candidate paradigm for investigating and quantifying this systematically.