## 2 Related Work
### Natural Interactions  
Natural interaction, where humans interact with machines in the same way as in human communication--through movements, gestures, or speech--is one of the possible solutions for intuitive interaction with 3D interfaces [14]. A natural user interface (NUI) allows users to interact with digital systems through intuitive, human-like actions, such as speech, hand gestures, and body movements that are similar to the way humans interact with the physical world. This approach moves away from traditional input devices such as keyboard, mouse, or touchpad [47]. Natural interactions are not necessarily 3D interactions, even though they are often used in 3D interfaces. We often associate the term NUI with natural interactions. They have the advantage that the user can use a wider range of basic skills when interacting than in conventional GUIs (e.g., UIs, which mainly rely on the mouse and keyboard for interaction) [48]. Much of the concept of natural interactions and interfaces is based on Microsoft's definitions and guidelines. [PERSON], a senior researcher at Microsoft, points out that NUI \"exploits skills that we have acquired through a lifetime of living in the world, which minimizes the cognitive load and therefore minimizes the distraction\" [49]. He also emphasizes that NUI should always be developed with the context of use in mind [49]. Gestures are seen as a technique that can provide more natural and creative ways of interacting with different software solutions. An important reason for this is the fact that hands are the primary choice for gestures compared to other body parts and serve as a natural means of communication between people [50]. In general, it is assumed that a UI becomes natural through the use of gestures as a means of interaction. However, when looking at the multi-touch gestures, e.g., on the Apple iPad [51], which are generally considered an example of natural interaction, it becomes clear that the reality is somewhat more complex. Some gestures on the iPad are natural and intuitive to the user, such as swiping left or right with one finger on the screen, which allows you to turn pages or move content from one side of the screen to the other, simulating the analog world. However, some gestures need to be learned, such as swiping left or right with four fingers to switch between applications. Such gestures are not intuitive for users and require additional learning, as it is not obvious how such an interaction should be performed. This requires an understanding of the relationship between the gesture and the action being performed [49]. By interaction types, NUIs can be divided into four groups: multi-touch (the use of hand gestures on the touch screen), voice (the use of speech), gaze (the use of visual interaction), and gestures (the use of body movements) [52]. Another new group of interfaces based on electrical biosignal sensing technologies can be added to this classification [53]. The emergence of multi-touch displays represents a promising form of natural interaction that offers a wide range of degrees of freedom beyond the expressive capabilities of a standard mouse. Unlike traditional 2D interaction models, touch-based NUIs go beyond flat surfaces by incorporating depth, enhancing immersion, and simulating the behavior of real 3D objects. This allows users to interact and navigate in fully spatial,multi-dimensional environments [54]. Touchscreen interactions are considered the most commonly used method for natural interactions as they are available on the most commonly used devices, such as smartphones and tablets. Voice user interfaces (VUIs) have experienced significant growth due to their ability to enable natural, hands-free interactions. They are usually supported by machine learning models for automatic speech recognition. However, they still face major challenges when it comes to accommodating the enormous diversity and complexity of human languages [55].