Interpretable Speech Features vs. DNN Embeddings: What to Use in the Automatic Assessment of Parkinson’s Disease in Multi-lingual Scenarios

Abstract

Individuals with Parkinson's disease (PD) develop speech impairments that deteriorate their communication capabilities. Speech-based approaches for PD assessment rely on feature extraction for automatic classification or detection. It is desirable for these features to be interpretable to facilitate their development as diagnostic tools in clinical environments. However, many studies propose detection techniques based on non-interpretable embeddings from Deep Neural Networks since these provide high detection accuracy, and do not compare them with the performance of interpretable features for the same task. The goal of this work was twofold: providing a systematic comparison between the predictive capabilities of models based on interpretable and non-interpretable features and exploring the language robustness of the features themselves. As interpretable features, prosodic, linguistic, and cognitive descriptors were employed. As non-interpretable features, x-vectors, Wav2Vec 2.0, HuBERT, and TRILLsson representations were used. To the best of our knowledge, this is the first study applying TRILLsson and HuBERT to PD detection. Mono-lingual, multi-lingual, and cross-lingual machine learning experiments were conducted on six data sets. These contain speech recordings from different languages: American English, Castilian Spanish, Colombian Spanish, Italian, German, and Czech. For interpretable feature-based models, the mean of the best F1-scores obtained from each language was 81\% in mono-lingual, 81\% in multi-lingual, and 71\% in cross-lingual experiments. For non-interpretable feature-based models, instead, they were 85\% in mono-lingual, 88\% in multi-lingual, and 79\% in cross-lingual experiments. On one hand, models based on non-interpretable features outperformed interpretable ones, especially in cross-lingual experiments. Among the non-interpretable features used, TRILLsson provided the most stable and accurate results across tasks and data sets. Conversely, the two types of features adopted showed some level of language robustness in multi-lingual and cross-lingual experiments. Overall, these results suggest that interpretable feature-based models can be used by clinicians to evaluate the evolution and the possible deterioration of the speech of patients with PD, while non-interpretable feature-based models can be leveraged to achieve higher detection accuracy.