Methodological contributions

Improving ecological validity

This PhD contributes to methodology in both neuroscience research and ET by using a combination of brain imaging and VR technology that not only promotes ecological validity but would also allow a participant or client to fully share the experience with a mental health professional. This was approached by combining mobile fNIRS with large IPT Octave. The choice of equipment was determined by priority to acquire good quality data and controllability of design without burdening participants with excessive uncomfortable equipment which might restrain natural movement and response, as well as potentially cause anxiety. The combination of these technologies immerses a user in a surrounding room-sized VR simulation that supports both natural locomotion and interaction with a simulation, in the space without losing the sight of one’s own body. This project demonstrated that this combination could be a useful tool for delivering VRET. Methodological contributions will inform the neuroscientific and VR community about the potential and advantages of combining wireless neuroimaging and large VR systems to bridge the gap between ecological validity and controllability of the design. This approach allows a more natural experience and response than previous combinations of VR and brain imaging used to evoke and measure fear inhibitory response and learning.

However, it should be noted, that this project compares its results to previous studies that employed non-consumer versions of HDMs. To date, there are no published peer-reviewed studies employing commercial wireless HMDs. Although currently, HTC Vive is available in a wireless version that allows untethered locomotion in VR, the design of the Vive HMD is not suitable to be combined with fNIRS without significantly destroying the headset in order to fit the prefrontal fNIRS set-up. As a part of this project,

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fNIRS was also tested with custom-adapted Oculus Rift (see appendix). Although it was possible to combine fNIRS with the HMD without losing the quality of simulation and fNIRS data, it came with the trade-off involving the comfort of wearing the technology. It is because some parts of Oculus Rift HMD were removed to fit fNIRS cap, however, those parts also support the placement of the HMD. Moreover, Oculus Rift currently is not available in the wireless version, therefore this project employed IPT technology.

Combining fNIRS with IPT

Although some previous studies employed brain imaging to investigate the impact of VRET on the brain activity, they used technologies that do not effectively balance the quality of measurement and naturalness of response. On the one hand, fMRI although it has a good spatial resolution, it restricts movement and therefore violates the naturalness of response. On the other hand, although current wireless EEG systems allow some locomotion, still they are significantly susceptible to motion artifacts and instrumental noise from VR devices, and they offer a low spatial resolution. Wireless fNIRS systems offer a compromise between fMRI and EEG. fNIRS is thought to impose a relatively less physical and psychological burden than fMRI, therefore, this technique could be advantageous for measuring neural responses during naturalistic tasks (Balardin et al., 2017), and also can be used in a vulnerable population, especially elders, infants or people with mental disorders (Cutini & Brigadoi, 2014; Irani et al., 2007). Moreover, fNIRS is more robust to motion artifacts and exogenous noise, therefore, provides a potentially better option for measurement in ecologically valid settings (Tuscan et al., 2013). However, it should be noted, that fNIRS due to the pressure imposed by optodes on the scalp might sometimes cause a risk to patients who suffer a migraine. In order to avoid the risk of potential headaches, participants wore the fNIRS device for maximum 30 minutes (including set up and data acquisition). Moreover, one participant who had a history of migraines was excluded from the study. In order to measure brain activity optodes must be secured and in proper contact with the scalp, therefore it is very difficult to minimise the pressure while maintaining a good signal. Although this project used standard NIRS optodes, the new developments in blunt-tip and flat-tip optode designs allow using more comfortable measurement, which perhaps would be more suitable to use in clinical applications.

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Employing wireless fNIRS within CAVE-like IPT VR offers a methodological advantage. Octave is a multisensory high-end VR laboratory which is larger than standard CAVE, therefore, it allows a more natural locomotion allowing for brain activity to be recorded in more naturalistic settings. The pilot study used an unprecedented combination of fNIRS and Octave to inform further research. Since these technologies were not combined before, the pilot study tested whether this endeavour is even achievable. The main concern was a possible signal interference between near-infrared light from Vicon tracking system and NIRSport. The pilot study assessed the signal-to-noise ratio to determine NIRS signal quality and demonstrated that peripheral devices in Octave did not significantly impact on the signal quality. However, this project found out that the level of movement might contaminate data with motion artifacts when combining fNIRS with IPT. This project proposed several resolutions to minimise motion artefacts and ensure signal quality such as reducing the level of motion. Especially leaning forward too excessively resulted in sudden spikes in the signal. While in the pilot study participants were allowed to move without any restrictions, during the two other studies they were advised about the level of motion. Additionally, improving the cap set-up, preparation and application reduced motion artifacts. For that reason the cap was upgraded with spring-loaded gromets, stiffing elements and a new retaining cap to allow better signal quality. This informs other researchers when combining fNIRS with VR for ecologically valid applications.

Combining psychophysiological monitoring with IPT

Several lessons regarding the usability of the equipment in VRET were learned during this project. Since the project was conceptualised, numerous test and efforts were made to set up and adapt psychophysiological monitoring devices. Especially several technical difficulties were encountered with HR and EDA monitors. Despite many adjustments and set-up modifications that were made after each study, unfortunately, this project demonstrated that the equipment was unsuitable for this kind of experiment. This outcome was particularly disappointing as psychophysiological data would be useful for hypothesis testing and validating the ability of VRET to trigger an emotional arousal within more ecologically valid settings.

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One of the most notable disadvantages of HR monitor – Zephyr Bioharness learned from this experiment was that the device is less usable in female participants. Due to the design of the Bioharness, it was very challenging to fit some female participants with the device due to the anatomy. Because most of the participants who took a part in the third study were females, most of the data was unusable, and therefore excluded from analysis. The validity and reliability of Bioharness were demonstrated in a few previous studies, however, one of the limitations of those studies was that the sample included only male participants (Hailstone & Kilding, 2011; Johnstone et al., 2012a, 2012b). Therefore a reasonable resolution must be found in order to make the Bioharness more usable for female participants. Moreover, because Bioharness is woven onto strap worn around the chest, it resulted in several sensor dislocations during data acquisition caused by the backpack worn for NIRS data recording device. Perhaps other types of multiple electrode-based wearable HR monitors would be more suited for this type of VRET research.

Although Edu-Logger Galvanic Skin Response (GSR/SCR) Sensor worked without issues during stationary tests, in the wireless mode there were several drops in Wi-Fi connection that resulted in a several failed transmissions and data loss. Unfortunately, despite several attempts to troubleshoot the issue, underlying problems could not be fixed. Moreover, no studieson reliability and accuracy of Edu-Logger GSR sensor were found. Although the sensor is a cost-effective solution for measuring EDA, the future studies should invest in a more reliable solution.