Choose Your Explanation: A Comparison of SHAP and GradCAM in Human Activity Recognition

Explaining machine learning (ML) models using eXplainable AI (XAI) techniques has become essential to make them more transparent and trustworthy. This is especially important in high-stakes domains like healthcare, where understanding model decisions is critical to ensure ethical, sound, and trustworthy outcome predictions. However, users are often confused about which explanability method to choose for their specific use case. We present a comparative analysis of widely used explainability methods, Shapley Additive Explanations (SHAP) and Gradient-weighted Class Activation Mapping (GradCAM), within the domain of human activity recognition (HAR) utilizing graph convolutional networks (GCNs). By evaluating these methods on skeleton-based data from two real-world datasets, including a healthcare-critical cerebral palsy (CP) case, this study provides vital insights into both approaches' strengths, limitations, and differences, offering a roadmap for selecting the most appropriate explanation method based on specific models and applications. We quantitatively and quantitatively compare these methods, focusing on feature importance ranking, interpretability, and model sensitivity through perturbation experiments. While SHAP provides detailed input feature attribution, GradCAM delivers faster, spatially oriented explanations, making both methods complementary depending on the application's requirements. Given the importance of XAI in enhancing trust and transparency in ML models, particularly in sensitive environments like healthcare, our research demonstrates how SHAP and GradCAM could complement each other to provide more interpretable and actionable model explanations.

Towards human performance on automatic motion tracking of infant spontaneous movements

Assessment of spontaneous movements can predict the long-term developmental outcomes in high-risk infants. In order to develop algorithms for automated prediction of later function based on early motor repertoire, high-precision tracking of segments and joints are required. Four types of convolutional neural networks were investigated on a novel infant pose dataset, covering the large variation in 1 424 videos from a clinical international community. The precision level of the networks was evaluated as the deviation between the estimated keypoint positions and human expert annotations. The computational efficiency was also assessed to determine the feasibility of the neural networks in clinical practice. The study shows that the precision of the best performing infant motion tracker is similar to the inter-rater error of human experts, while still operating efficiently. In conclusion, the proposed tracking of infant movements can pave the way for early detection of motor disorders in children with perinatal brain injuries by quantifying infant movements from video recordings with human precision.

EfficientPose: Scalable single-person pose estimation

Human pose estimation facilitates markerless movement analysis in sports, as well as in clinical applications. Still, state-of-the-art models for human pose estimation generally do not meet the requirements for real-life deployment. The main reason for this is that the more the field progresses, the more expensive the approaches become, with high computational demands. To cope with the challenges caused by this trend, we propose a convolutional neural network architecture that benefits from the recently proposed EfficientNets to deliver scalable single-person pose estimation. To this end, we introduce EfficientPose, which is a family of models harnessing an effective multi-scale feature extractor, computation efficient detection blocks utilizing mobile inverted bottleneck convolutions, and upscaling improving precision of pose configurations. EfficientPose enables real-world deployment on edge devices through 500K parameter model consuming less than one GFLOP. The results from our experiments, using the challenging MPII single-person benchmark, show that the proposed EfficientPose models substantially outperform the widely-used OpenPose model in terms of accuracy, while being at the same time up to 15 times smaller and 20 times more computationally efficient than its counterpart.