The paper discusses the unique challenges faced in Alzheimer's disease (AD) detection tasks, which are characterized by significant within-class variation (WCV) due to the continuous nature of cognitive decline in AD patients. Unlike standard classification tasks, AD detection models need to account for varying degrees of cognitive impairment among individuals diagnosed with AD.
The authors propose two novel methods to address these challenges:
Soft Target Distillation (SoTD): This approach uses a sample score estimator to generate soft targets that capture the confidence or severity level of each sample. The classifier is then trained using soft cross-entropy loss, which incorporates the awareness of sample-level differences.
Instance-level Re-balancing (InRe): This method estimates the probability density of samples based on their AD severity levels, measured by log-probability ratios. The sample losses are then re-weighted inversely proportional to their probability densities, effectively addressing the instance-level imbalance.
Experiments on the ADReSS and ADReSSo datasets, using BERT and RoBERTa features, demonstrate that both proposed methods significantly improve the performance of AD detection models compared to the baseline. The authors also provide insights into the effectiveness of the ensemble estimation (EE) approach over the refinery estimation (RE) approach for generating robust soft targets.
Furthermore, the analysis reveals that the baseline classifiers exhibit unstable training results due to over-fitting, while the InRe method effectively alleviates this issue and stabilizes the training process.
This work presents an important step towards developing more robust and reliable AD detection models that can better capture the nuances of cognitive decline in individuals with Alzheimer's disease.
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