# A Review of Recent Literature on Audio-Based Pseudo-Haptics
## 3 Discussion  
With the rapid advancement of technology, immersive technologies are experiencing unprecedented popularity. These technologies not only serve entertainment purposes but also find extensive applications in training in the form of immersive virtual learning environments (iVLEs) and serious games and virtual simulations in particular. With respect to iVLEs, a notable gap exists in their focus, with most emphasizing cognitive and affective skill development due to the challenge of simulating touch inherent in psychomotor skills, which requires specialized and cost-prohibitive haptic devices that are not widely accessible at the consumer-level. To address this limitation, the field of pseudo-haptics has emerged. Pseudo-haptics leverages alternative sensory modalities, primarily vision, to replicate the tactile experience without relying on physical haptic devices. This approach has been successfully applied across various domains [66] to provide, for example, sensations of weight, stiffness, roughness, reliefs, slipperiness, and stickiness [67; 68; 69]. Various reviews have considered visual-based pseudo-haptics, including [PERSON] and [PERSON] [70], who explored best design practices to develop haptic simulations for learning, [PERSON] and [PERSON] [71], who focused on haptic technology for mobile AR, [PERSON] et al. [72], who focused on haptic solutions in VR, and [PERSON] et al. [36], who focused on user representation in virtual environments. These specific reviews concluded that by manipulating visual cues, the users were able to perceive alteration in the sense of touch, such as changes in weight, force, friction, and stiffness. A similar conclusion was also reached by [PERSON] and [PERSON] [73], who examined haptics as an interaction modality. A thorough review is also provided by [PERSON] and [PERSON] [40], who discuss the design of visual-based pseudo-haptic applications for a variety of applications, including training, assistance, and entertainment. Although the majority of pseudo-haptics work has focused on visual cues, [PERSON] and [PERSON] [33] underscored the potential of inducing pseudo-haptics using sound or a combination of auditory and visual cues in their review published in 2019. Expanding on this insight, our narrative review delved into the existing literature exploring audio-based or audiovisual-based pseudo-haptics, analyzing 26 relevant studies. These studies were conducted across various levels of realism and across a range of platforms, including PC, AR, VR, and mixed reality (MR). A summary of the findings of our review is presented in Table 1. Overall, the results strongly support the efficacy of audio-based and audiovisual-based pseudo-haptics. The results also suggest that manipulating factors such as frequency, pitch, loudness, delay, and attenuation time can alter perceptions of weight, stiffness, roughness, dampness, force, and glossiness. Playing recorded audio representations of textures successfully conveyed the impression of different surfaces. Furthermore, several studies indicate that integrating sound and/or visual stimuli to simulate haptic sensations enhances immersion, realism, and overall performance. In their review, [PERSON] et al. [74] examined weight perception in VR using multimodal illusion, particularly visual-audio interaction. They found that auditory perception of weight included change of pitch, different sound of footsteps, loudness, and faster beat to increase force magnitude and lower frequency. Although [PERSON] et al. [74] focused on perceived weight changes, their overall findings align with the ones observed in this review. [PERSON] and [PERSON] [71] described how sound can influence gesture perception, indicating that users can learn gestures associated with specific sounds and kinesthetic force in AR.