# A Review of Recent Literature on Audio-Based Pseudo-Haptics
## 2 The Review  
### Audio-Haptic Interactions  
Unlike visual-auditory and visual-haptic interactions, audio-haptic interactions remain significantly underexplored [33]. [PERSON] and [PERSON] [33] emphasized that auditory cues can effectively convey information about object size, properties, and texture, particularly through the sounds produced when interacting with the material. Prior to the COVID-19 pandemic, our own work focused on multimodal interactions, beginning with a series of experiments that examined the interactions between sound and visuals within virtual environments, and revealed that sound can have significant effects on both visual fidelity perception and task performance, albeit these effects are subjective [49]. This work was expanded to examine audio-haptic interactions, and more specifically, the effect of sound on haptic fidelity perception within the context of a virtual drilling task; that is, drilling to a pre-defined depth within a virtual block of wood using a virtual drill [50]. Results revealed that sound related to the task (i.e., contextual sound) led to higher haptic fidelity perception. However, a follow-up experiment that examined accuracy in a virtual drilling task found that neither contextual or non-contextual sound showed any significant difference in drilling accuracy, although accuracy was higher in the presence of sound (contextual or non-contextual) than no sound at all [50]. It was concluded that further work is necessary to account for the experimental shortcomings, including a lack of a dynamic sound stimulus (e.g., the drilling sound remained constant throughout the entire drilling process) [50]. [PERSON] et al. [51] conducted a study where they compared recorded sounds and sounds recreated by participants when interacting with different surfaces. Eighteen participants  
Figure 1: Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flow diagram summarizing the review process. were seated at a table and the realism of these sounds and their impact on participant perception tested. More specifically, eighteen participants engaged with three sound conditions: (i) recorded sound, (ii) sound generated by the participant as they interacted with the surface, and (iii) white noise to block ambient sounds. In all three conditions, the participants wore headphones. Black curtains and a foam board were used to eliminate visual cues from the texture. The task of the participants was to interact with a textured surface by dragging a tool across it. The tool, equipped with a position and force sensor, recorded both the sound and the user's motion during the interaction. The participants were then asked to rate 30 conditions (10 textures, each played three times in a random order). Results indicated that while sound alone (Condition i) affected participants' judgments of the roughness and hardness of the texture, the sound produced as the participant interacted with the textured surface (Condition ii) was most effective at capturing the surface texture's roughness and hardness compared to haptic cues alone (Condition iii), while slipperiness was primarily determined by haptic cues. As [PERSON] et al. [52] pointed out, physical interaction with real-world objects elicits haptic feedback, but also causes mechanical excitations that induce vibrations, often leading to audible sounds. They devised a method to synthesize realistic sound and vibrotactile stimuli from geometric representations and object material properties at three different scale levels (macro, meso, and micro) in a virtual environment. Micro-texture surfaces consisted of flat with either a glossy or matte texture, whereas as meso- and macro-texture surfaces had a single ridge, bump, sine wave, and sawtooth patterns. Vibrotactile actuators were used to provide the haptic feedback, which was generated by tracking the user's hand pose.