## 3 Materials and Methods
### Proposed AR System
#### 3.1.2 Interface Design  
Our prototype was crafted to enhance the accessibility and engagement of AR experiences by integrating audio feedback within an image-based application. This approach addresses the need for inclusive AR solutions in domains such as education and entertainment, where 3D object imposition onto real-world imagery is prevalent [25; 26].  
* Touchscreen Interaction-Based Audio Interface (TAI)  
Common AR applications often display virtual objects atop real-world elements, such as books or image markers, or on flat surfaces like tables or walls [1]. Sighted users typically interact with this digital overlay through AR-enabled devices like iPads and smartphones using touchscreen interaction (e.g., [26]). For individuals with visual impairments, however, discerning what is shown on the screen poses a significant challenge. Our system addresses this by presenting AR virtual objects overlaid on images, which users can interact with directly on the AR device's screen. Contact with specific objects triggers auditory information describing the item being touched--for instance, touching a virtual tree could produce the sound of rustling leaves, which stops when the user ceases contact.  
Moreover, virtual objects within AR are typically positioned in a 3D space, a concept that may be challenging to grasp via a 2D interface for some individuals, for example children with visual impairments. Previous studies have highlighted the necessity for tools and methods that facilitate the acquisition of spatial skills by children with visual impairments [19]. Our solution to this limitation involves audio modulation related to the proximity of the virtual objects; the sound volume increases as the object approaches the AR camera and decreases as it moves away. This method allows users to not only identify the virtual objects but also to comprehend their spatial positioning by correlating their location on the screen with the volume of the sound.  
The development of this AR feature was accomplished using the Unity 5.x and Vuforia SDKs 10.22. Figure 2 illustrates the configuration of the AR device and how users interact with virtual objects on the screen.  
Natural Interaction-Based Audio Interface (NAI)  
The advent of advanced AR Head-Mounted Displays (HMD), such as Microsoft HoloLens and Apple Vision Pro, has introduced a user interface that supports natural and intuitive interaction, allowing users to interact with digital objects directly, without the need for touchscreen interactions [27]. The growing use of AR content viewed through HMDs prompts a valuable exploration into how children with visual impairments can comprehend virtual objects without needing a tangible interface. Our approach enables users to physically touch the virtual objects, at which point they receive corresponding audio feedback and sound effects. For instance, when a user touches a representation of a house, they might hear sounds of people conversing within, thereby supporting the formation of a mental model of a spatial 3D world.  
For the implementation of this AR functionality, we utilized the Vuforia SDK and Unity, coupled with ManoMotion SDK 2.0 for advanced hand-tracking capabilities. Figure 3 illustrates the configuration of the AR device setup and a user interacting with virtual objects through direct hand movements.