## 2 Materials and Methods
### Materials  
The MR group used Microsoft HoloLens 2 devices to study a holographic representation of the human muscular system. The HoloLens 2 is a head-mounted display that projects 3D images onto the user's field of view, creating a mixed reality environment. The device has a resolution of 2048 \(\times\) 1080 pixels per eye, a field of view of 52 degrees, and a refresh rate of 60 Hz. The device also has a built-in speaker, microphone, and camera, allowing the user to interact with the hologram by using voice, gesture, and gaze commands. The hologram used in this experiment was developed by Case Western Reserve University, as a free app called HoloAnatomy, and displayed both different colours for muscle groups and labels for the most important muscles, as shown in Figure 3.  
The PPT group used a laptop computer and a projector to view a PowerPoint presentation on the human muscular system. The presentation consisted of 1 slide, containing the front and rear views of the human muscular system, and text pointing to the major muscles in the body. The presentation was designed so that it covered the same content, and provided the same level of detail, as the hologram.  
The multiple-choice tests were chosen to measure the learning outcomes because they have several advantages in our research context. In this case, the main advantage of the multiple-choice tests is that they are easy to administer and evaluate, especially when a digital platform such as Google Forms is used. This made it possible to collect and analyse the participants' responses by efficiently using simple statistics. Second, multiple choice tests can cover a wide range of content and be used to assess different levels of understanding, extending from the recognition of facts to the application of concepts [42; 43]. Questions were designed to reflect the learning objectives of the research and to establish if the learning method that uses the HoloLens 2 device is more efficient than the traditional method that uses PowerPoint presentations when the human muscular system is studied.  
In designing the content, goals, and other aspects of the different implementations, we drew on the guidelines and recommendations of previous studies that used MR devices (such as HoloLens) to enhance the learning outcomes of students in various domains. We also consulted with experts in the field of human anatomy and physiology to ensure the accuracy and relevance of the content, and to establish the goals of the learning material on the human muscular system. To ensure the even-handed treatment of the two research groups (students who studied the human muscular system by using the HoloLens 2 device, and students who studied this with a traditional PowerPoint presentation) to the greatest possible extent, we made sure that there were no significant differences between their IQ level and prior knowledge of the topic. The same learning objectives, content, and duration were also applied to both groups, who did not receive additional instruction nor guidance. The only difference was the mode of delivery, with one group receiving instruction through MR (using the HoloLens 2 device), and the other through PowerPoint.