# A Review of Recent Literature on Audio-Based Pseudo-Haptics
## 4 Conclusions  
This overview examined the recent use of haptics-based applications in virtual environments, with a specific emphasis on audio-based pseudo-haptics. Pseudo-haptics uses auditory and/or visual cues to simulate the perception of touch, a challenging sense to replicate in virtual environments without dedicated haptic devices. The manipulation of auditory cues has been shown throughout the literature to result in perceptual adjustments in haptic attributes such as material texture, weight, roughness, dampness, and stiffness. Consistent with decades of research into cross-modal phenomena in the physical world, the use of audio in the virtual world has been shown repeatedly to influence haptic perception.  
While the focus of much past pseudo-haptics research has been on the use of visuals, sound is a growing area of important research showing that other sensory inputs also influence our haptic perception. However, there is still considerable work to be done. Many questions remain as to how to best leverage sound to compensate for the loss or reduced fidelity of haptic stimulation. There is little work, for instance, on differences across different user populations (ages, genders, cultures, sensory abilities, and so on). Understanding these differences could help in designing more universally effective systems or allowing different parameters of personalization. Moreover, what are the optimal characteristics of audio cues (e.g., frequency, amplitude, temporal dynamics) that best enhance the perception of different aspects of pseudo-haptics? Identifying these parameters can aid in creating more realistic and convincing tactile illusions. We also know little about the critical timing thresholds for synchronizing audio cues with visual and proprioceptive feedback to maximize the illusion of haptic feedback. Furthermore, all of the studies presented took place over short time periods. How do users adapt to audio-based pseudo-haptics over extended periods, and what are the long-term effects on their sensory perception and motor skills? Longitudinal studies could reveal potential benefits or drawbacks of prolonged use.  
The surge in popularity of immersive technologies, particularly driven by the shift to virtual learning during the COVID-19 pandemic, has seen the widespread adoption of pseudo-haptics across diverse fields. In areas such as medical training, where the acquisition of tactile skills is paramount, pseudo-haptics has emerged as a valuable tool. While it cannot completely substitute for intricate haptic feedback, pseudo-haptics serves as a viable alternative when sophisticated haptic devices are unavailable.  
**Author Contributions:** Conceptualization, S.A., B.K., A.D. and K.C.; methodology, S.A., B.K., A.D. and K.C.; formal analysis, S.A., B.K., A.D. and K.C.; investigation, S.A., B.K., A.D. and K.C.; writing--original draft preparation, S.A. and B.K.; writing--review and editing, S.A., B.K., A.D. and K.C.; supervision, B.K. and A.D.; project administration, B.K. and A.D.; funding acquisition, B.K. and A.D. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC) in the form of a Discovery grant to [PERSON], the Ontario Tech University Research Excellence Chair to [PERSON], and through an Ontario Graduate Scholarship to [PERSON].  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflicts of interest.