FedSER-XAI: PSO-optimized multi-stream cross-attention transformer with graph features for explainable federated speech emotion recognition

Federated learning for speech emotion recognition faces fundamental challenges in simultaneously achieving high performance, privacy preservation, and model interpretability. This paper introduces FedSER-XAI, a novel framework that integrates Particle Swarm Optimization (PSO)-based feature selection, multi-stream cross-attention mechanisms, and graph-based feature extraction within an explainable federated learning architecture. Our approach combines Vision Transformer processing of mel-spectrograms with temporal-spatial graph convolutional networks to capture both contextual and structural speech relationships. The PSO algorithm achieves 78.1% dimensionality reduction (228→50 features) while improving discriminative power. The multi-stream architecture processes traditional acoustic features alongside novel graph-based representations derived from visibility and correlation graphs, fused through Transformer-based cross-attention mechanisms. Extensive evaluation on EMODB and SAVEE datasets demonstrates exceptional performance: 99.9% and 97.2% accuracy in centralized settings, with remarkable federated performance achieving global model accuracies of 99.7% (EMODB) and 97.2% (SAVEE) across 8 emotion-specialized clients, representing only 0.2% and 0.0% degradation compared to centralized training. The framework achieves rapid convergence within 10 communication rounds, representing minimal performance degradation (0.2% for EMODB) while preserving privacy. Cross-dataset evaluation on CREMA-D yields 68% accuracy, demonstrating reasonable generalization. The comprehensive explainability framework using SHAP and LIME provides global and local interpretations, validating that graph-based features contribute significantly to emotion discrimination. FedSER-XAI represents the first explainable federated speech emotion recognition system, advancing trustworthy AI for sensitive healthcare and human-computer interaction applications.