Speech foundation models in healthcare: Effect of layer selection on pathological speech feature prediction

Accurately extracting clinical information from speech is critical to the diagnosis and treatment of many neurological conditions. As such, there is interest in leveraging AI for automatic, objective assessments of clinical speech to facilitate diagnosis and treatment of speech disorders. We explore transfer learning using foundation models, focusing on the impact of layer selection for the downstream task of predicting pathological speech features. We find that selecting an optimal layer can greatly improve performance (15.8% increase in balanced accuracy per feature as compared to worst layer, 13.6% increase as compared to final layer), though the best layer varies by predicted feature and does not always generalize well to unseen data. A learned weighted sum offers comparable performance to the average best layer in-distribution (only 1.2% lower) and had strong generalization for out-of-distribution data (only 1.5% lower than the average best layer).