exHAR: An Interface for Helping Non-Experts Develop and Debug Knowledge-based Human Activity Recognition Systems

Human activity recognition (HAR) is crucial for ubiquitous computing systems. While HAR systems are able to recognize a predefined set of activities established during the development process, they often fail to handle users' unique ways of completing these activities and changes in their behavior over time, as well as different activities. Knowledge-based HAR models have been proposed to help individuals create new activity definitions based on common-sense rules, but little research has been done to understand how users approach this task. To investigate this process, we developed and studied how people interact with an explainable knowledge-based HAR development tool called exHAR. Our tool empowers users to define their activities as a set of factual propositions. Users can debug these definitions by soliciting explanations for model predictions (why and why-not) and candidate corrections for faulty predictions (what-if and how-to). After conducting a study to evaluate the effectiveness of exHAR in helping users design accurate HAR systems, we conducted a think-aloud study to better understand people's approach to debugging and personalizing HAR systems and the challenges they may encounter. Our findings revealed why some participants had inaccurate mental models of knowledge-based HAR systems and inefficient approaches to the debugging process.