Explaining Human Activity Recognition with SHAP: Validating Insights with Perturbation and Quantitative Measures

In Human Activity Recognition (HAR), understanding the intricacy of body movements within high-risk applications is essential. This study uses SHapley Additive exPlanations (SHAP) to explain the decision-making process of Graph Convolution Networks (GCNs) when classifying activities with skeleton data. We employ SHAP to explain two real-world datasets: one for cerebral palsy (CP) classification and the widely used NTU RGB+D 60 action recognition dataset. To test the explanation, we introduce a novel perturbation approach that modifies the model's edge importance matrix, allowing us to evaluate the impact of specific body key points on prediction outcomes. To assess the fidelity of our explanations, we employ informed perturbation, targeting body key points identified as important by SHAP and comparing them against random perturbation as a control condition. This perturbation enables a judgment on whether the body key points are truly influential or non-influential based on the SHAP values. Results on both datasets show that body key points identified as important through SHAP have the largest influence on the accuracy, specificity, and sensitivity metrics. Our findings highlight that SHAP can provide granular insights into the input feature contribution to the prediction outcome of GCNs in HAR tasks. This demonstrates the potential for more interpretable and trustworthy models in high-stakes applications like healthcare or rehabilitation.

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.