Measuring Physiological Responses in a VR Environment Using Empatica’s E4 and Faros 360
In various cognitive science studies, researchers are interested in physiological data under different conditions. Empatica’s E4 and Faros 360 are two commercially available and popular devices to obtain such data. E4 wristband measures blood volume pulse, inter-beat interval, electrodermal activity and temperature. Faros 360, positioned centrally on the chest, is a device recording heart rate measurements. Previous research  has shown that the data obtained with Faros is reliable, but the problem arises with the E4’s measurements due to the movements of the participants. We designed an experiment, where we measured physiological responses with Faros and E4 in a motion-controlled VR environment. We will use Faros measurements as a reference point and compare its data to E4 to determine its reliability. Our research question was: What is the data quality of E4 when measuring physiological signals in a motion-controlled VR environment?
We conducted a within-subject design to check for intra-individual realiabilty. Participants were exposed to two VR scenes while wearing both devices. The second scene was expected to elicit a high degree of arousal, whereas the first supposedly should lead to a milder response. After each scene, participants completed questionnaires reporting on their VR experience.
We anticipate differences in physiological parameters between the first and second scene. We expect the heart rate to be higher during the second and lower during the first scene compared to the baseline. We anticipate positive correlations between participants' experiences, as reported in questionnaires, and their physiological responses. Given that participants did not move their hands, we expect the results from E4 and Faros 360 to be similar. However, we expect the results obtained from Faros 360 to be more accurate.
The E4 on the participant's non-dominant hand required them not to move that hand. Despite this warning it turned out to be quite challenging for many of them to follow this instruction resulting in a potential motion artifact.
Even though we expect the E4 results to be as reliable as those from the Faros 360 in a controlled VR environment, we have concerns about its broader usability due to the requirement for not moving. Regarding further research, it would be interesting to conduct a similar experiment using different VR scenarios or longer movie clips to observe E4's measurements.
 T. Gruden, K. Stojmenova, J. Sodnik, and G. Jakus, “Assessing drivers’ physiological responses using consumer grade devices,” Applied Sciences, vol. 9, no. 24, p. 5353, 2019. doi:10.3390/app9245353