## 2 Literature Review
Finally, our research studied the application of VRET in arachnophobia treatment, incorporating Arduino bio-sensors to collect real-time bio-data from subjects. Bio-data are integrated with the VRET system data and stored in SQL database for data mining and real-time VRET level adjustment is used to minimize over-exposer to the treatment [18]. Driving is an essential skill that facilitates independence and mobility of individuals in modern society and is often a requirement of employment. Being diagnosed with a driving phobia limits an individual's work options and creates issues associated with social interaction when mass transportation or transportation for hire is not available or unaffordable. According to emotional processing theory, successful exposure therapy leads to new and more neutral memory structures that overrule old memories that provoke and heighten anxiety [19]. In a VRET for driving phobia pilot study, 14 subjects with serious driving phobia were placed into a series of experimental conditions, including psychotherapeutic, medical examination, psychotherapy sessions, VRET sessions, and a final behavioral avoidance test (BAT) when driving in traffic. The therapy session for each subject required 10 days to complete the experiment. After 6 to 12 weeks, follow-up tracking of the subjects was performed to access the subjects' driving performance and evaluate the effectiveness of the treatment for each subject. The follow-up tracking indicated that 13 out of the 14 patients maintained successful treatment results [20]. Another VRET experiment for driving phobia used eight females who were willing to try VRET but unwilling participants used in vivo exposure. The VRET exposure environment consisted of eight sessions which gradually exposed participants to increasingly uncomfortable exposure over 50-minute intervals. Factors, such as mean mood, anxiety, cognitive evaluation, quality of life, sense of presence, subjective discomfort, and heart rate were recorded during the experiment. The result showed that the sense of presence decreased as the session progressed while subjects' subjective discomfort scores and heart rate increased. After the experiment, subjects were determined to be more confident with their driving ability. Six out of eight subjects were willing to conduct in vivo exposure after VRET [21]. A VRET experiment for driving phobia related to fear of driving in tunnels was conducted. In the virtual reality environment, the car passes through a tunnel with lighting adjusted to resemble natural daylight on entry and exit, with increasing darkness and increasing lightness upon exit. The sound of traffic was also included to enhance the realism of the simulations [22]. The above driving phobia VRET studies provide a solid basis for continued research. The numbers of subjects in these studies are generally too small to draw a decisive conclusion or provide suggestions for future VRET refinement. Moreover, most of the literature evaluated their VRET system based on subjects' driving performance, and few focused on the subjects' biological senses and system recorded data analysis. Therefore, this pre-test experiment will examine the feasibility of using biological sensors and system-data collection and analyses to measure subjects' driving performance to ensure the safety and effectiveness of VRET toward phobia treatment. Further, to ensure the VRET is scientifically conducted, collecting real-time bio-data of patients is vital during the ET sessions. Matured bio-sensor solutions, such as the Arduino micro-controller, can transmit bio-data to a remote computer or cloud database using an XBee wireless network [23].