# The Sense of Agency in Human-Machine Interaction Systems
## 5 Discussion
### The Impact of the Operator's Experience on the Dynamically Changing SoA  
HMI systems are designed as long-lifespan solutions that can be used frequently. As the period of time using an HMI system increases, the operator's understanding, trust, and operation proficiency of the machine improves, because human operators have strong learning abilities, regardless of whether it is intentional learning or unconscious concomitant learning. Therefore, in the process of using HMI systems, the operator's SoA changes dynamically. [PERSON] et al. [32] defined agency as an autonomous organization that adaptively regulates its coupling with its environment and contributes to sustaining itself as a consequence; therefore, as agents, humans will adaptively regulate their coupling with HMI systems in the process of using them for a higher SoA. A stable HMI state can be achieved after a long time using the HMI system. This is critical because, in most cases, out-of-the-loop problems are caused by operators' over-reliance on machines. For the SoA that changes dynamically due to changes in the operator's experiences and subjective feelings, the overall SoA of a period can be assessed. Based on the dynamic change in the operator's SoA, the use of an HMI system can be separated into three stages:  
* Initial stage: After the minimum learning time, the operator has just started to use the HMI system, and the SoA is greatly affected by the operator's subjective feelings. * Transition stage: At this stage, the operator's proficiency in using the HMI system gradually increases over time, so the transparency and performance gradually improve, which finally leads to an increase in the SoA. * Stable stage: The operator has mastered the HMI system proficiently and acquired plenty of experience and an unconscious CM. At this stage, the SoA reaches a stable high state. Most of the HMI systems in the literature are in the initial stage. Of course, there are a few experiments with a simple design, a short transition stage, and a quick entry into the stable stage. However, very few papers focus on the impact of the operator's experience on the SoA. Even in studies that set up long-term experiments or simpler experiments including the above three stages, they only analyzed the overall SoA or the transient SoA and did not analyze the dynamic change process of SoA. [PERSON] et al. [152] pointed out that only a few research works have observed the dynamic changes in the SoA, and none have attempted to automatically model the dynamic behavior of the human SoA in real time within natural or complex settings. However, the SoA measurement methods proposed by [PERSON] et al. [36] and [PERSON] et al. [112; 113] for HMI systems show potential for measuring the dynamically changing SoA of humans. Investigating the impact of an operator's experience on the dynamically changing SoA, therefore, presents a valuable area for future research. To guide future research in this area, we propose the following theoretical framework:  
* Phase Definition and Characterization: Clearly define the three phases of HMI use: initial, transitional, and stable. Identify key characteristics and measurable variables for each phase (e.g., subjective perception, proficiency, transparency, and performance). * Dynamic SoA Measurement: Leverage and improve existing SoA measurement methods [36; 112; 113] to capture real-time changes in the SoA. Develop or adopt tools that can automatically simulate dynamic human SoA behaviors in natural and complex environments [113]. * Experiential Factors: Investigate the specific factors that lead to SoA changes in each phase (e.g., learning mechanisms, trust development, and operator's mental models). Distinguish between conscious and unconscious learning accompanying learning processes. * Longitudinal Studies: Design long-term studies that track operators' SoA over a longer period of time to observe transitions between phases. Include frequent and detailed evaluations to capture subtle changes in the SoA.