Effect of interactive vs. passive virtual reality on pain threshold and tolerance

Study design

A within-subjects experimental study design was used to evaluate the effect of VR on the response to pain stimuli. The study was conducted at Qassim University’s female campus in Saudi Arabia in 2019 and was approved by the Subcommittee of Health Research Ethics, Deanship of Scientific Research at Qassim University.

Sample and sample size

The study included 53 female university students. The students were screened and excluded for the following conditions: migraine, neurological disorders, impaired vision, epilepsy, or motion sickness. Each participant signed an informed consent before enrollment. Exact estimates of effect size were unavailable; therefore, we calculated the required sample size based upon the assumption of a ‘medium’ effect size. Power analysis for three measurements, a power of 0.80, an alpha level of 0.05, and a medium effect size (F=0.25) was performed in G*Power [20]. G*Power is a free downloadable software; the user specifies the desired test and the input parameters (mentioned above), and the software will calculate the output parameters, including the required sample size and exact level of power. The minimum sample size required was 28. To ensure accurate estimates, we enrolled 53 participants [21].

Virtual reality equipment and conditions

The equipment used to administer the VR experience included the Acer Nitro 5 Gaming Laptop, Intel Core i5-7300HQ, GeForce GTX 1050 Ti, 15.6″ Full HD, 8 GB DDR4, 256 GB SSD, AN515-51-55WL and Oculus Rift + Touch Virtual Reality System. The VR headset was placed on the participant’s head for two rounds of assessment: VR interactive and VR passive. The interactive round included a game entitled ‘Summer Fun Land Maze Manor,’ which required the participant to solve a puzzle. The passive round included a video entitled ‘Epic Roller Coaster,’ which depicted a roller coaster ride with a 360° view of the environment. The passive game could be described as watching only and did not require any interaction by the participant.

Data collection

Participants completed a brief interview about demographic information, health status, and previous use of VR. Each participant completed a baseline assessment followed by two VR conditions: VR interactive condition and VR passive condition. To eliminate any order effects, the interactive and passive conditions were given in random order sequence, which had been established prior to the fieldwork using computer-generated sequencing. For the baseline assessment, each participant submerged her non-dominant hand into an ice bath at 5 °C (±1.5 °C) without wearing the VR headset. The ice bath was approximately 2 L in size and did not circulate. It contained a thermometer for continuous monitoring, and the temperature was maintained by either adding or removing chunks of ice. The participant’s hand did not touch any part of the container. The researcher started the timer when the hand entered the ice bath. When the participant gave the first verbal indication of pain, such as saying “Ah” or telling the researcher that the pain had started, the threshold time was recorded. The participant kept her hand in the ice bath and the timer continued. Tolerance was recorded at the point when the participant removed her hand from the ice bath. Once removed, the participant placed her hand in a warm heater for 30–45 s in order to normalize the hand temperature. There was a 5 min rest period between assessment rounds.

For the VR rounds, the participant wore the VR headset and received brief instructions to the game. The participant started the game, and after 30 s of playing, the participant’s non-dominant hand was submerged into the ice bath by the researcher. The same protocol as the baseline round was followed (i.e., threshold = first indication of pain; tolerance = removal of the hand from the ice bath). Heart rate was assessed with a finger monitor before and after the baseline assessment as well as after each of the VR rounds. Once the participant completed all the VR rounds, the researchers conducted a brief interview inquiring how immersed the participant felt during the VR (rated on 10-point scale), whether any side effects occurred, whether it was comfortable (rated on 10-point scale), and whether she would be interested in using it again in the future (yes/no). All assessments were completed in a single session that took approximately 20 min.

Data analysis

Descriptive statistics were used to characterize the data on demographic characteristics, VR experience, VR immersion, and VR comfortability (all collected before and/or after the experiment). Repeated measures ANOVA (within the general linear model command in SPSS) were conducted to evaluate pain threshold, pain tolerance, and heart rate. Overall F-tests indicated the significance for the comparison across baseline, VR interactive condition, and VR passive condition. Post-hoc analysis indicated the level of significance for the individual comparisons between conditions.

Interactive vs. passive VR

The finding that interactive VR conditions resulted in longer times for pain tolerance supports earlier studies’ findings [17, 18, 22, 23]. For the most part, the argument has been made that interactive VR conditions require the participant to engage with the game, which results in a more distracted state of mind. In the case of pain sensation, pain requires a person’s attention, and therefore by distracting the person’s attention, one can reduce the pain sensation. However, there are competing theories about the mechanism by which interactive VR is more effective than passive VR. In a recent review, Gupta et al. proposed that there are neurophysiologic mechanisms at work, and this theory has been supported by studies using VR and biofeedback in combination [24], [25], [26]. The question is whether the ability to manage pain can extend beyond the period that the person is wearing the VR device. If pain reduction only occurs in that fixed period, then the mechanism is likely distraction, but if the patient learns a skill during the VR exposure that he/she can employ beyond that VR experience to manage pain, then perhaps a new mechanism can be proposed.

Users’ experience

The overall results showed minimal side effects when using VR. The side effects noted were temporary dizziness and motion sickness. Earlier studies also showed that VR-based gaming provided an analgesic effect with minimal side effects [27]. Considering the benefits of pain tolerance, VR is potentially a more suitable analgesic for painful medical procedures than pharmaceutical interventions. Furthermore, the participants gave high ratings for their level of immersion as well as the comfortability of the headset. Comfortability has improved over time as the equipment has decreased in size and weight, and studies have reflected this through participant reports. This only bolsters the adaptability and potential application of VR both medically and non-medically.

Study strengths and limitations

The study strengths included using an experimental design in controlled conditions as well as using an objective assessment of pain tolerance (i.e., when the participant removed her hand from the water bath). However, the assessment for pain threshold may have been subject to bias because the participant had to verbally indicate to the researcher when the pain sensation began. The study was sufficiently powered, and the study sample size was comparable to those in earlier studies. The participants were female university students, which provided evidence of the VR effect in an adult population. However, the generalizability of study findings may be limited because the study did not include male participants. The university setting at Qassim University is segregated by gender, so it was not feasible for the female research team to recruit male participants.