# A Review of Recent Literature on Audio-Based Pseudo-Haptics
## 1 Introduction  
The technologies of video games, virtual worlds, and social networks have become collectively known as immersive technologies [1] and can blur the boundary between the physical and virtual worlds while immersing the user [2]. Although historically, the strongest demand for immersive technologies has come from the entertainment industry (video game players have generally been early adopters), immersive technologies have found wider applications in industries as diverse as health care, education, the military, and real estate [3]. A growing area of immersive technologies is education/training in the form of immersive virtual learning environments (iVLEs), which may be used as an umbrella term for innovations such as virtual simulations and serious games. These offer learners an engaging, cost-effective, and safe training environment. The use of iVLEs shifted from a \"backburner training tool to a first-choice strategy for ensuring individual, team, and system readiness\" as we moved to remote learning to facilitate lockdowns/stay-at-home orders during the COVID-19 pandemic [4]. There are many benefits to remote learning, including the removal of geographical boundaries, flexibility (for the educators and learners), and being a more environmentally friendly option (reduced driving to/from educational institutions), and thus it is likely that remote learning will continue to increase. According to Straits Research, the global virtual learning (e-learning) market was estimated at USD 215 billion in 2021 and is estimated to reach an expected value of USD 645 billion by 2030 at a compound annual growth rate (CAGR) of 13% during this period [5]. Within the umbrella of virtual learning, the global serious games market size was valued at USD9 billion in 2022 and is projected to reach USD 32.73 billion by 2030 (a CAGR of 18.41%) given the growing demand for interactive learning experiences [6]. Often with many iVLEs, particularly virtual simulations and serious games, the goal is to immerse the user into a scenario that faithfully recreates reality and responds to their actions accordingly. To accomplish this, knowledge of the human senses is imperative. The human senses have been defined as the physiological capacities that provide data for perception [7], allowing humans to establish relations with the physical world [8]. Going back over 2000 years, the philosopher [PERSON], who was one of the first to systematically examine the human senses, classified the five traditionally recognized and widely accepted senses as sight (vision), hearing (audition), smell (olfaction), taste (gustation), and touch (somatosensation) based on the physiological properties of humans along the biological (\"sensory\") receptors (specialized neurons) of the human body, and more specifically, the eyes, ears, nose, and hands, respectively, that respond to specific sensory information [8]. Detection of sensory information by sensory receptors results in a sensation, and the way that this sensory information is organized, interpreted, and consciously experienced is known as perception [9]. Although the five senses have become \"conventional wisdom,\" many scientists and philosophers have argued that this idea is outdated and inaccurate, and we now know that we can detect stimuli beyond these five traditional senses (e.g., temperature, pain, and balance, amongst others) [10]. However, while humans do perceive through other modalities beyond the five traditional senses, they are often considered extensions or derivatives of the primary senses rather than separate entities [11]. Of the five senses, it has been argued that sight is the most important and most complex. There exists much more research on sight than on the other sensory modalities [12], and the public believes that sight is the most important of the senses despite the limited empirical data to support this [13].