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CiTrus: Squeezing Extra Performance out of Low-data Bio-signal Transfer Learning
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Proposes CiTrus, a convolution-transformer hybrid with masked auto-encoding and frequency-based pre-training, plus a resampling-based fine-tuning method and a cross-validated evaluation for low-data bio-signal transfer learning from SleepEDF EEG.
Problem
Transfer learning for bio-signals with small labeled downstream datasets: which architectures and pre-training strategies transfer well from large EEG pre-training to other bio-signals, and how to fairly evaluate them given high test-fold variance.
Approach
A CNN encoder (channel-independent via batch concatenation) feeds a PatchTST transformer trained with masked auto-encoding; it adds a frequency (spectrogram) reconstruction pre-training task, multimodal EEG+EOG pre-training, and a resampling-based fine-tuning that aligns sampling rate to the pre-training data instead of interpolating length.
Key results
- CiTrus (s) achieves the best accuracy and ROC/PRC on HAR (80.71 ACC, 93.03 ROC) in the table, and CiTrus (fp) achieves the best ACC on ECG (82.44) at the lowest data regime.
- Frequency pre-training (CiTrus fp) gives the largest average gains on the lowest and highest data regimes, with pre-training improvements up to +12.9% on PPG.
- The proposed resampling-adaptive fine-tuning improves over temporal interpolation in almost all cases, with PPG gains reaching about 64% and overall improvements up to about 60%.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use frequency-based rather than conventional time-domain pre-training (ablation) | CiTrus · PPG | accuracy: 58.57 -> 65.25 | Helped |
| Use frequency-based rather than conventional time-domain pre-training (ablation) | CiTrus · SleepEDF | accuracy: 73.87 -> 48.69 | Hurt |
| Add multimodal pre-training (ablation) | CiTrus · EMG | average improvement across ACC, ROC, and PRC: -2.0 | Hurt |
| Add multimodal pre-training (ablation) | CiTrus · ECG | average improvement across ACC, ROC, and PRC: -0.8, +0.5, +1.8 | Mixed |
| Add multimodal pre-training (ablation) | CiTrus · PPG | average improvement across ACC, ROC, and PRC: +7.1, +3.3, -1.4 | Mixed |
| Add multimodal pre-training (ablation) | CiTrus · Gesture | average improvement across ACC, ROC, and PRC: +9.1, +3.0, -0.4 | Mixed |
| Add multimodal pre-training (ablation) | CiTrus · SleepEDF | average improvement across ACC, ROC, and PRC: +0.1, -4.0, -1.8 | Mixed |
| Use multimodal rather than unimodal pre-training (ablation) | CiTrus · EMG | average improvement across ACC, ROC, and PRC: +6.3, +8.1, +3.1 | Helped |
| Use multimodal rather than unimodal pre-training (ablation) | CiTrus · SleepEDF test set | average improvement across ACC, ROC, and PRC: -4.7, -3.0, -3.2 | Hurt |
| Use the resampling-adaptive fine-tuning approach instead of temporal interpolation (ablation) | CiTrus (p) · PPG | average improvement across ACC, ROC, and PRC: +49.4, +51.0, +47.3 | Helped |
| Use the resampling-adaptive fine-tuning approach instead of temporal interpolation (ablation) | CiTrus (fp) · Gesture | average improvement across ACC, ROC, and PRC: +9.0, +2.8, +3.4 | Helped |
| Use the resampling-adaptive fine-tuning approach instead of temporal interpolation (ablation) | CiTrus (fp) · SleepEDF | average improvement across ACC, ROC, and PRC: -22.1, -18.9, -9.3 | Hurt |
Surprising findings
- Variance across test folds is much larger than across random seeds, up to about 4609% higher variance.
- Pre-training is not necessary for EMG and FD-B; a convolutional model trained from scratch outperforms other models on FD-B.
Limitations
- Frequency pre-training performs poorly on some datasets (e.g., SleepEDF and Gesture high-data regimes, EMG and FD-B fp variants near chance)
- Pre-training not beneficial for EMG and FD-B and Epilepsy datasets
- SleepEDF evaluation averaged only over random seeds due to time constraints, not 10-fold
Experimental setup
Datasets: SleepEDF EMG Gesture Epilepsy FD-B PPG HAR ECG
Benchmarks: EMG ECG PPG HAR FDB Epilepsy Gesture SleepEDF
Metrics: accuracy ROC AUC PR AUC
Baselines: PatchTST bioFAME SimMTM TFC NLPatchTST
Builds on: PatchTST bioFAME SimMTM TFC
Closest papers by meaning
- Pre-Training Graph Contrastive Masked Autoencoders are Strong Distillers for EEG (ICML 2025 · similarity 0.85)
- EEGPT: Pretrained Transformer for Universal and Reliable Representation of EEG Signals (NeurIPS 2024 · similarity 0.84)
- Neuroformer: Multimodal and Multitask Generative Pretraining for Brain Data (ICLR 2024 · similarity 0.84)
- Standing on the Shoulders of Giants: Rethinking EEG Foundation Model Pretraining via Multi-Teacher Distillation (NeurIPS 2026 · similarity 0.83)
- Population Transformer: Learning Population-level Representations of Neural Activity (ICLR 2025 · similarity 0.83)
- Leveraging unlabelled data for generalizable neural population decoding (NeurIPS 2026 · similarity 0.83)
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