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2020,  2 (4):   316 - 329   Published Date:2020-8-20

DOI: 10.1016/j.vrih.2020.07.004
1 Introduction2 Biological microscope recognition and experiment simulation 2.1 Key knowledge points of microscope operation 2.2 A conceptual model of microscope simulation 2.3 Optical adjustment simulation 2.4 VR based microscope operation 2.5 AR-based microscope instructions 2.6 Microscope operating instructions 3 System implementation 3.1 System structure 3.2 Outcome 4 Discussion and conclusions 4.1 Experimental results and discussions (1) Discussion of learning effects(2) Discussion of learning attitudes 4.2 Usability analysis of virtual experiment 4.3 Conclusion 4.4 Improvements and future work

Abstract

Background
Mixed-reality technologies, including virtual reality (VR) and augmented reality (AR) , are considered to be promising potential tools for science teaching and learning processes that could foster positive emotions, motivate autonomous learning, and improve learning outcomes.
Methods
In this study, a technology-aided biological microscope learning system based on VR/AR is presented. The structure of the microscope is described in a detailed three-dimensional (3D) model, each component being represented with their topological interrelationships and associations among them being established. The interactive behavior of the model was specified, and a standard operating guide was compiled. The motion control of components was simulated based on collision detection. Combined with immersive VR equipment and AR technology, we developed a virtual microscope subsystem and a mobile virtual microscope guidance system.
Results
The system consisted of a VR subsystem and an AR subsystem. The focus of the VR subsystem was to simulate operating the microscope and associated interactive behaviors that allowed users to observe and operate the components of the 3D microscope model by means of natural interactions in an immersive scenario. The AR subsystem allowed participants to use a mobile terminal that took a picture of a microscope from a textbook and then displayed the structure and functions of the instrument, as well as the relevant operating guidance. This flexibly allowed students to use the system before or after class without time and space constraints. The system allowed users to switch between the VR and AR subsystems.
Conclusions
The system is useful for helping learners (especially K-12 students) to recognize a microscope's structure and grasp the required operational skills by simulating operations using an interactive process. In the future, such technology-assisted education would be a successful learning platform in an open learning space.

Content

1 Introduction
Various biological processes and micro-objects are invisible to the naked eye and to understand this knowledge, learners should possess the ability of abstract thinking, which makes it difficult for children to learn science. Microscopes are considered a necessary essential instrument for observing and manipulating the micro-world[1]. Therefore, students are required to operate a microscope practically in K-12 biology education. Owing to the technological progress of virtual reality (VR) and augmented reality (AR) (e.g., imagination, interaction and immersion), over the last decade, VR/AR has emerged as an potentially effective tool for helping students to improve their knowledge and practical skills through education[2], especially, macro-layer experiments (e.g., three-dimensional simulation of the motion of celestial bodies) and micro-layer experiments (e.g., macromolecular structures). Scholars have found that AR, or the combination of VR and AR, can improve learning efficiency and cultivate positive emotions[3-6]. Furthermore, it was found that there is a positive correlation between presence and the perceived affective quality of learning[7]. With the popularization of related hardware devices supporting VR and AR applications, several VR and AR technologies have been applied to education, such as magnetic field experiments[8,9], biology lab courses[10], and geometry courses[6]. With mobile learning becoming more and more popular[11,12], there are positive trends toward integrating VR, AR and mobile technologies in education especially in the era of future open educational spaces[13].
The AR technologies used in science education reside in two categories, image-based AR and location-based AR[14]. Image-based AR (including marker and markerless technology), is conducive to developing students' spatial abilities, practical skills, and their understanding of concepts through real-time interactive simulation experiments[14-16]. For example, in teaching chemistry, image-based AR can be used to present the micro components of substances in real-time and be combined with specific markers to complete virtual interactive learning, which is conducive to students' intuitive understanding of chemistry[17] By integrating image-based AR and mobile technology into physical experimental simulations, conveniently and effectively to assist students in experimental operations by using ubiquitous mobile phones, students will be enabled to operate experiments in real-time without being limited by experimental instrumentation[18]. One of the most common image-based ARs in K-12 education is AR book, which particularly focuses on the sciences for secondary high school students[13]. Another is a location-based AR that is conducive to scientific inquiry and is usually combined with a geographical setting for learning, real-time data, and needs a large space[14]. The application of VR technology in education improves contextuality and the intuitive aspect of knowledge presentation with deep interactivity and strong immersion. It offers students a rich and varied personalized learning environment and provides opportunities for active exploration and interactive communication[19,20]. By building a virtual laboratory and allowing students to conduct virtual experiments in a virtual environment, students are assisted in remembering, understanding, and improving their ability to analyze and solve problems[21,22]. The platform NOBOOK developed by Beijing Lebu Company involves physical, chemical, and biological virtual experimental resources for secondary school education (www.nobook.com). Despite advances in VR/AR, the creation of meaningful content consistent with domain knowledge using this technology is still extremely challenging.
The conventional learning approach in biology laboratory courses usually involves teachers using a laboratory manual or textbook to guide students on the use of laboratory equipment. In the last decade, either VR or AR has been applied to microscope experiments[10,23]. An existing biology microscope simulation system with a keyboard and mouse was used to manipulate a virtual microscope[23]. The advantage was that simplified basic operations were quickly executed without needing additional interactive equipment. The disadvantage was that the lack of realism in the experimental operations resulted in students finding it difficult to understand the operating principles of the microscope. An interactive app module ArBioLab developed using image-based AR technology involves a microscope environment that complies with the basic biology laboratory manual[10]. ArBioLab's AR microscope experiment resources are manipulated using mobile devices, these being a good platform for flexible future education, but there is no function designed to guide students to learn standard operational processes (e.g., text or voice). However, most of them are pure VR or pure AR, and without using head-mounted displays for human-computer interaction produced a weak sense of reality and a poor interactive experience.
A study of previous research on virtual microscope simulation experiments confirms that image-based AR experiments can be combined successfully with mobile devices and be applied to textbooks to achieve real-time virtual cognitive learning but lacks the guidance for students to complete standard experimental operations. Desktop VR experiments can be completed with the user interface, but it does not simulate the natural interaction behavior of humans to operate the instrument accurately. This causes students to misunderstand the microscope’s operating principles.
In this study, immersive VR and image-based mobile AR were used to simulate the operation of microscopes. The image-based mobile AR technology was used to simulate the process of operating the microscope. Through interaction with the UI and audio support, students were guided to learn the standard operations of the experiment with the experimental material being only a textbook. Immersive VR technology was used to construct a self-guided three-dimensional virtual learning environment and simulate real microscope operations with an interactive VR device for students to undertake the experiment without actual experimental instruments. AR experiments can be used for real-time assisted learning of microscope use, while the VR environment was designed to simulate a real experiment to help students autonomously master the correct experimental operations with supplementary learning guidance. This demonstrated empirically that using modern technology to increase students' interest in autonomous learning is also an effective auxiliary method for experimental education.
2 Biological microscope recognition and experiment simulation
2.1 Key knowledge points of microscope operation
As a required biology knowledge point for secondary school students, they should understand the main structure and functions of the optical microscope, and correctly master the experimental operation skills. The steps for operating the optical microscope mainly include taking out and setting up the microscope, adjusting the light, making observations, and cleaning the microscope, amongst which adjusting the light and observation are the key steps.
While adjusting the light processes, the order of steps is as follows: raising the lens tube to the highest position; aligning the low magnification objective lens with the light aperture; adjusting the mirror to maximize the amount of light emitted through the aperture.
During the observation processes, the key operating steps are as follows: installing the slide; adjusting the distance between the objective lens and the slide for the objective lens to be close to the slide; focusing the eyepiece.
2.2 A conceptual model of microscope simulation
To provide sufficient intuitive support for learning how to operate a microscope, VR and AR technologies were combined to develop a simulated operational system. In this work, certain components of a microscope model are described in a detailed three-dimensional model, and an entire microscope structure was generated according to these topological interrelationships. They were the chief virtual objects operating in the VR and AR scenarios. We specified the motion interrelations among components during the operation processes and the interactive operation during the simulation process. Figure 1 illustrates the approach of the microscope operation simulation.
A created three-dimensional microscope model was the interactive object for the virtual experiment. The three-dimensional model closely approximated a microscope’s physical form and the topological interrelationship between each component was constructed using 3ds Max. Autodesk 3ds Max was chosen as the 3D modeling software to build the 3D virtual microscope, because in comparison with other modeling platforms, it has the efficient modeling methods, effects, and rendering quality required for fine modeling. The optical microscope had twelve main components: eyepiece, objective lens, lens tube, nosepiece, arm, stage, stage clips, aperture, coarse focus knob, fine focus knob, mirror, and base. The three objective lenses were mapped to have magnification powers of 4×, 10×, and 40×. Each component embodied its functional properties.
3ds Max mainly includes the polygon, geometric, compound object, two-dimensional graphics, and NURBS modeling methods. The characteristics of these modeling methods are shown in Table 1. Since the microscope is a unit with multiple components that are either structurally regular or irregular, the model of each component was completed individually by comprehensive utilization of the polygon modeling, geometric modeling, and compound object modeling methods according to the characteristics required. Finally, the component models were assembled into a three-dimensional microscope model.
The modeling methods of Autodesk 3ds Max
Modeling method Characteristics
Polygon modeling

Changes the geometric structure of the model by altering the arrangement of points, and is used to

add details to the model.

Geometric modeling

Uses basic geometry to build a simple model, and model sizes can be adjusted by changing the size

parameters of the geometry.

Compound object modeling

Combines multiple geometries into a new one, and the methods include connection, lofting, Boolean

operations, etc.

2D graphical modeling

The two-dimensional shape composed of multiple splines is transformed into a three-dimensional

model by the editing commands such as extrude, rotate, etc.

NURBS modeling It is mainly used for surface modeling, and is suitable for building complex surfaces.
To realize the simulated operation of a microscope, the relative motion between microscope components should be defined. In this work, the motion interrelationships among the microscope components were divided into the hierarchical relationship and control relationship. In the Unity3D development platform, the motion direction and motion rate of the subclass components are consistent with those of the parent component, but the motion of the subclass parts did not affect the motion state of the parent parts. The parent-child relationship between microscope components was set according to the standard experimental procedures for microscopes. The main parent-child relationship was generated between the nosepiece and the objective lens and among the lens tube, the eyepiece, and the nosepiece. A controlling relationship was defined as arising when a moving component controlled the movement of other related components. According to standard processes, during the experimental operation the vertical movement of the lens barrel was controlled by rotating the coarse focusing knob and the converter controlled the motion state of the objective lens. A text message described the operation of the warning key.
2.3 Optical adjustment simulation
When adjusting the light, the principles of light reflection should be considered. The basic principle is that when the light is reflected, the incident light, the reflected light and the normal are on the same plane, and the reflected light and the incident light are separated on both sides of the normal, and the reflection angle is equal to the incident angle, as shown in Figure 2a. According to the mathematical model, the reflected ray OB had to be calculated, where AO is the incident ray, OB is the reflected ray, the normal vector OP is vertically halved AB, and ON is the unit normal vector. The calculation formula (1) of reflected light can be obtained by calculating.
O B = A O - 2 ( A O O N ) O N
In this study, the reference projection plane of the light source was defined, as shown in Figure 2b, as being divided into 11×11 piece small blocks with the center of each block regarded as the incident point of the light source. Thereby, the reflected light in the experiment was calculated in real-time according to the mathematical model of light reflection. The light adjustment was completed on the assumption that the amount of reflected light entering the light-aperture was greater than 100.
2.4 VR based microscope operation
To improve experientially the virtual experiments in the VR experiment, HTC VIVE has the advantages of an accurate 360-degree head-mounted display, realistic graphic display, directional audio, and high-definition haptic feedback, it simulates natural interaction for users to interact with the virtual environment and offers exciting virtual world experiences in a small real space. As technology develops, the performance of such devices is improving and the cost is reducing; therefore, the HTC VIVE virtual reality device was used to operate the three-dimensional microscope model. The association between the VR handheld controller and microscope operation is shown in Table 2.
The correlation between VR handheld controller and microscope operation
Handle key name Microscope operation
Touchpad Rotating coarse/fine focus knob, nosepiece
Holding button Pick up slide, Rotate reflector
Menu button Choose different types of slides
Trigger button Click once, open the stage clips and click twice, close the stage clips
Collision detection is an important aspect of virtual reality systems. High-precision, real-time collision detection technology plays a vital role in enhancing the practicability of 3D simulation. The hierarchical bounding box algorithm[24] was used for microscope simulation. The collider was constructed for the nosepiece, coarse focus knob, fine focus knob and other components such as the slide of the microscope required for interaction. All colliders should match the shape of components of the microscope as much as possible for collision detection to be accurate. This work took advantage of the built-in physics engine in Unity3D precisely to achieve this goal. The coarse focus knob collider is shown in Figure 3. In the VR experiment, the VR handheld controller collided with the microscope components to activate corresponding operations, such as rotating the coarse focus screw and the mounting and demounting procedures. In addition, the trigger was realized by the collider and was activated by the collision between the colliders and this trigger event was used to detect whether each step of the microscope operation was performed correctly and completed.
2.5 AR-based microscope instructions
In the AR experiment, we defined an image of a microscope from a biological textbook or experim-ental course as the real object, the 3D model of the microscope and its components with properties were virtual objects. Consequently, a database was established for storing the learning materials, such as the images of a microscope, the images of observations using the microscope, the function descriptions in text, and the audio instructions for operating the microscope. We used the images captured from the microscope laboratory course or textbook for recognition. The virtual scenes included a three-dimensional model of the microscope and its interactive behavior. The AR-based microscope interaction processes are shown in Figure 4. User Interface (UI) controls were defined to represent different magnifications of the objective lenses (e.g., 4×, 10×, and 40×) with different types of slides and joysticks for simulating the microscope’s operation, and a display window for the slide image. The microscope operation experiment was conducted on a mobile device by means of gesture interaction or voice. Furthermore, the function of each component in the microscope was inquiry-based.
Image-based augmented reality technology was used to activate 3D microscope models and interaction behaviors corresponding to the content of a biological textbook. Registration based on natural features is popular for ease-of-use without adding abstract markers. The microscope image in the biological teaching material was applied for identification. Information on the features of the recognition image was extracted. Real-time binarizing was applied to the color images captured by the camera, and then feature information for each image was extracted. Afterward, by employing the feature matching algorithm, the features in each video stream image were matched to the features of the recognition image. After matching successfully the transformation matrix between images was calculated in real-time. The registration process is shown in Figure 5. The position of the camera's angle of view was obtained based on the calculated transformation matrix, the video stream image taken by the camera was then, merged with the three-dimensional virtual scene in real-time, with the real image being used as the background, and the virtual scene being superimposed on it. Finally, the microscope could be operated on the mobile device using the touch screen.
2.6 Microscope operating instructions
The microscope simulation was standardized according to the standard operation of a microscope, and the guiding instructions that described all operational steps for the microscope experiment was designed. Furthermore, this module could also record how learners manipulated the device while being tested. The experimental guidance process is shown in Figure 6. To facilitate learners knowing whether their operation processes were timeously correct, the guiding results were fed back via the UI in real-time. The “UI press” is green when the operation is correct and is white when the operation is incorrect.
3 System implementation
The system’s target groups are teachers and K-12 students. The teachers are comfortable in the knowledge, that they can use the non-immersive VR subsystem to demonstrate the structure and how to manipulate the instrument in a class. The students can use the system to understand the microscope’s structure and acquire the correct skills to complete virtual scientific experiments. The system provides a VR subsystem (including a non-immersive VR system and an immersive one) and an AR subsystem. The system allows learners to switch between the VR and AR subsystems according to requirements and conditions.
3.1 System structure
The VR/AR-based three-dimensional biological microscope simulation and operational guidance system was oriented toward secondary school education. The experimental system consisted of a VR-based and AR-based microscope experiment and contained two learning units: microscope structure and microscope operation. The system structure is shown in Figure 7. The learning materials included images of a physical biology microscope for recognition and 3D microscope models with standardized properties and operational specifications. The VR system was implemented using Unity3D the VRTK plug-in, and the AR system was implemented using Unity3D with the Vuforia SDK, and was compiled for mobile and tablet platforms or PCs. Unity3D was used to write script code for the digital scenes, interactive controls, and user interface. Since natural image recognition has been integrated into Vuforia SDK, we used it to construct images as markers to match to the corresponding 3D objects, detect the images, and then link the corresponding images to the database.
The realization of the VR-based microscope operation simulation was as follows: First, the topological motion interrelationships among the various components of the microscope were set. Second, the operating guidance was compiled according to the microscope’s standard operating procedures. The system supported automatic evaluation of whether the user's operation met the specifications. Specific experimental content included the simulation of microscope operation, observation, 3D user interfaces, and image observation in the display window. In the VR experiment, the immersive virtual reality device was used to interact with the microscope model. In the AR experiment, the mobile devices were used to operate the microscope and display a 3D object obtained from the VR model. The process sequence was as follows: First, using a mobile camera, learners took a photo of an image in a biological textbook. Then the photo was recognized. Finally, this triggered the display of AR content, including images and 3D models as overlays onto the screen. The system allows learners to switch to the VR subsystem for operating the 3D models in immersive scenes.
3.2 Outcome
The VR/AR-based three-dimensional simulation and operation guidance system is convenient for selecting an experimental subsystem using the UI shown in Figure 8a. Figure 8b and 8c show the UI and the VR-based microscope experimental subsystem’s operating scheme. The subsystem’s functions mainly include microscope recognition, operational guidance, image display, the interactive microscope, and the selection of slides. The models can be manipulated by rotating, zooming, and through investigation promote recognition of the structure and functions of the microscope, such as the objective lenses, coarse focus knob, and fine focus knob. The system provides operating guidance to alleviate learner’s cognitive burden. The main operations included mounting slides and operating the microscope to observe the slide image in different objective lenses.
Figure 8d and 8e show a few screenshots of the AR-based microscope operation experiment subsystem. Learners can operate the model and use the UI to control it, while simultaneously observing the results of the operation using the mobile device. The learners could select the microscope’s various components to master their nomenclature and functions. For learning the interactive operation, when observing the onion epidermal cell illustrated in Figure 8e, the power of the objective lenses can be dynamically switched (4×, 10×, 40×) by linking to the existing cell observation images. The mobile AR subsystem is flexible for students to use pre-class or after-school without being constrained by time and space.
4 Discussion and conclusions
The main objective of this study was to provide students with a new auxiliary learning method for a microscope experiment using VR/AR technology. The virtual experiments were tested on students from the perspective of learning effects, learning attitudes and usability, and were then discussed based on the experimental results. Finally, future research for improvements was formulated based on the information obtained from the experiment.
4.1 Experimental results and discussions
The experimental subjects were freshmen and senior junior-high school students, who operated the virtual experiments. During the experiment, changes in the students' learning attitudes were recorded. After the experiment, the students participating in the experiment were required to write out the microscope experiment’s operational steps. Figure 9 shows student participation in the experiment.
(1) Discussion of learning effects
The freshmen were divided into two groups during the first learning experiment. One group studied the content of the textbook and took the learning test, and then conducted the actual experiment and compared them. The other group initially used the mobile AR experiments to assist in learning from a textbook and recorded the learning effects then undertook the VR experiment and these learning results were tested and lastly, they conducted the real-life operational experiments to check the learning effect. The experimental environment settings for the senior and new students were similar.
According to the experimental results, in comparison with the traditional learning method, the AR-assisted learning method had a positive impact on the new students’ theoretical knowledge of new students’ the first experimental learning. After learning under the VR experimental conditions, basically, the students had mastered the operational process being taught. Compared with students who learned without VR support, the new students’ final practical operation experiment results were all satisfactory. For senior students, the auxiliary learning effects of AR were not significant, but after practicing under the VR experimental conditions, they could correctly operate the equipment and the learning effects were significantly better than those students without the VR learning experience.
The experimental results showed that VR/AR had a significant effect on assisting new students’ learning, and had a positive influence on helping the students to master experimental skills. After the students used the AR experiment to understand the experimental theoretical content of the textbook, the VR experiment effectively helped the students to learn independently the experimental method of operation and the learning effects were close to those of the actual experimental operation. For the senior students, the effects of AR-assisted learning were not significant, because they already had a grasp of the theoretical knowledge being tested.
(2) Discussion of learning attitudes
The students who used VR/AR-assisted learning had powers of concentration similar to the students without VR/AR-assisted learning, but autonomous learning requires more initiative and interest, and also promotes mutual learning and communication among students. Students who used AR-assisted learning thought that it helped them learn the theoretical aspects of microscope use and VR-assisted learning had a significant positive impact on the practical execution of the experiment.
4.2 Usability analysis of virtual experiment
Based on the reviews of students participating in the experiment, there are suggestions for improving the utility of an auxiliary experimental learning system based on VR/AR. The following were the opinions compiled:
(1) In the AR experiment, a video about the experiment could be added, which would assist students to preview and review the standard experimental process.
(2) The key operations in the experiment could be emphasized in the form of text using AR, combined with the operation in the AR experiment thus enhancing the learning memory of students.
(3) In VR experiments, the sense of experience would be closer to reality by adding some simulation content about biology laboratories in school. When an error occurred in the operation, a voice prompt could be combined with the operating guide for the error to be corrected timeously.
4.3 Conclusion
Virtual reality and augmented reality were combined to develop an operation simulation system for understanding a microscope’s structures and functions and mastering standard operating skills in secondary school biology education. The system provided a VR subsystem (including non-immersive and immersive VR systems) and an AR subsystem. This allowed learners to switch between the VR and AR subsystems according to their requirements and the device conditions. A 3D model of a microscope was built accurately and the relative motion among components was specified during the operational process. The microscope model components’ hierarchical and control interrelationships were reasonably specified using Unity3D for simulating interactive behavior. The operating guide was defined and compiled. The VR subsystem focused on simulating the interactive behavior of a microscope for learners to practice microscope manipulation in an immersive scenario. The experimental results demonstrate that the learning effect of experimental operation based on immersive VR is similar to the actual operation of a microscope. Wearable devices allow students in junior high school to foster positive emotions and motivate self-learning. The AR subsystem focused on assisting learners to understand the structure of a microscope and become familiar with the experimental procedures before entering the laboratory. The objective is simplicity and portability. From the analysis of the experimental results the mobile AR subsystem had a positive effect on students’ comprehension of theoretical subject matter, and without being constrained by time and space allowed for pre-class or after-school use. VR and AR are potential aided-learning tools for future educational experiences and learning environments across other K-12 educational contexts and in open-learning spaces. In the future, such simulations would be optimized to enhance their realism.
4.4 Improvements and future work
This research has great potential and utility to help students develop knowledge of and comprehend basic experimental theory and master basic experimental operations. Through empirical research, microscope experimental learning tools based on VR/AR should be improved. We also proposed several aspects where the research can be continued.
In terms of system design:
(1) To enrich the function of experiments based on VR and AR, it is necessary to emphasize the core content for students accurately to learn key and difficult content.
(2) The user interface of learning tools will be improved to make it easier for students to use.
In terms of experimental design:
(1) Two single variable control groups were added. One group studied under the AR experimental conditions, the other group studied under the VR experimental conditions, and analysis of the variances between these groups has already encouraged research into other differences and advantages of AR and VR in auxiliary experimental learning contexts.
(2) Measurement of the long-term learning effect of experimental learning based on VR/AR. Once the experimental groups complete the process, the students' theoretical knowledge and mastery of the actual experimental operation should be examined to test the long-term effectiveness of microscope experimental learning based on VR/AR.

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