Virtual reality
Virtual reality (VR) technology is evolving at a fast pace and its use as a professional training tool has drastically increased in the past decade.
VR is an immersive technology that simulates a user’s physical presence and allows for interaction within a computer-generated environment. It is usually achieved through the use of specialized hardware and software, such as head-mounted displays (HMDs) and motion tracking sensors (Sherman & Craig, 2002).
Virtual reality for training
VR can be used as a training tool in many different areas (Narciso et al., 2020). Among these areas, its use is particularly relevant to medical education (e.g. Mao et al., 2021), the military (Binsch et al., 2021) and the aerospatial domain (Pirker, 2022). In these areas, field practice is a crucial part of the initial training, when professionals need to learn, repeat, and perfect accurate technical gestures.
In the military or aerospatial fields, VR has the advantage to simulate dangerous situations without exposing trainees to real physical risk. It also makes it possible to repeat scenarios in a fully controlled environment without monopolizing large facilities that are expensive to set up and maintain. Finally, it allows the trainees to learn by themselves and repeat the lesson as long as they feel it necessary.
The efficiency of VR training has been very recently explored in the health domain, for novice or future surgeons. One study explored the performance of novice orthopedic surgeons following VR training or classical training consisting of a demonstration by a surgeon and a video of the surgery (Xin et al., 2018). Following VR training, novice surgeons had a significantly higher accuracy in performing the technical gesture than students who underwent classical training. Another research team explored VR training efficiency for novice surgeons (Barré et al., 2019).They focused on subjective reports of physical comfort and workload. Following VR training, novice surgeons reported less mental workload during real surgery and less postural discomfort than surgeons who did not undergo this training.
From these two medical studies, it can be extrapolated that VR training is efficient in improving manual skills and reducing mental workload when performing the task in real conditions.
However, some researchers found conflicting results on the topic of VR-related learning and mental workload. In a study focusing on students who had to follow a laboratory class, a classical video tutorial on PC was shown to improve knowledge retention better than a VR demo (Makransky et al., 2017). However, it is important to underline that even if the students could manipulate relevant laboratory tools in VR, the transfer test concerned only theoretical knowledge and not manual abilities. Moreover, learning was not tested with objective measurements, but assessed as learning beliefs in participants (i.e. how much the participant thought they had learnt). The authors also found an increase in mental workload during VR demos, as measured with EEG.
Altogether, the results reported above suggest that while VR training has advantages for motor and visuo-spatial learning, it is not beneficial for theoretical knowledge acquisition. This means that training goals should be in adequacy with VR benefits, and it appears that VR fits particularly well for learning the spatial organization of an environment and the motor sequence to perform a specific task. These latter characteristics make VR a very promising tool for procedural airplane pilots training, where learning the spatial layout of the cockpit and specific motor procedures to interact with it are crucial elements.
Advantages of VR training for pilots
VR training has several advantages over simulator training for airplane pilots. From a learning and pedagogical view-point, VR has the potential to provide a higher sense of immersion and presence, leading to a more realistic training experience for the pilot. Moreover, VR training allows providing immediate feedback to the pilot, enabling them to identify and correct mistakes in real time. Additionally, previous studies have shown that VR training can lead to greater visuo-spatial and procedural training gains than standard training tools(Alexander et al., 2005; Barré et al., 2019; Kozhevnikov & Garcia, 2011; Xin et al., 2018), allowing pilots to better learn and retain important skills.
VR training also has several advantages from a logistical and organizational viewpoint. It is significantly less expensive than simulators, making it a more accessible training option for pilots and training organizations. Similarly, VR systems are more portable than simulators. Finally, VR training can be conducted remotely, making it more convenient and accessible for pilots who may be unable to travel to a physical training location.
VR drawbacks and potential adverse effects
Although VR presents various advantages for airplane pilots training over more canonical tools (e.g. simulators), some adverse effects have hindered its adoption on a larger scale. When exposed to virtual environments, especially using head-mounted displays, one may experience discomfort going from eye strain to nausea and disorientation. These effects were initially thought to be similar to simulator sickness, but they actually differ, in particular in terms of ocular fatigue (Stanney et al., 1997), that would be greater for cybersickness, and causal mechanisms. This phenomenon is known as cybersickness.
Cybersickness can occur both in static and moving environments. In static environments (i.e. where the only movements are those of the participants, as for example when participants are seated and asked to look around), cybersickness is thought to be related to the time elapsing (lag) between the participants movements and the visual feedback displayed, and more specifically to the difference between the virtual and physical head pose (Palmisano et al., 2020). On the other hand, in moving environments (the most common example being rollercoaster simulated environment) the cause of cybersickness is thought to be the conflict between the vestibular (signaling an absence of motion) and the visual (signaling motion) feedback (K. Stanney et al., 2020). Importantly, pilots can face both static and moving environments during training (e.g. training on procedures to be performed at the gate, before taxiing vs. training on procedures to be performed in cruise phase).
The incidence rate of cybersickness varies between 60 and 95% of the general population at their first exposure, depending both on technology and stimulation experienced while in the virtual environment (K. M. Stanney et al., 2003; Yildirim, 2020). Moreover, contrary to motion sickness, with which it shares symptoms and possibly underpinning physiological causes, cybersickness incidence rate appears to be higher in the older population than in children (Arns & Cerney, 2005). An hypothesis to explain this greater susceptibility could be that the perceptual system in adults in more finely tuned to real motion than in children. The exposure time inducing sickness symptoms is usually shorter in a virtual environment than in transport systems (Cobb et al., 1999)and emerges within the first 10 minutes.
There exists a core of symptoms that are more frequently reported in association with cybersickness and that are those explored, for example, by the Simulator Sickness Questionnaire (SSQ) (Kennedy et al., 1993): visual fatigue (e.g. blurred vision, headache, dry eyes), disorientation (the loss of one’s sense of direction or of one’s position in relationship with the surroundings, a general state of confusion with regard to time and place) and nausea.
In the context of training of airplane pilots, the symptoms pertaining to vision are particularly important, due to the specific sight requirement that this population is subjected to in order to be declared fit for duty (Manual of Civil Aviation Medicine, 2012)
Specific risk for visual health
Even if a virtual environment looks “real” with a high-definition screen, the viewing condition through a headset is very different from natural viewing for the visual system. This is mainly due to the vergence-accommodation conflict. Vergence corresponds to the contraction of ocular muscles to rotate ocular globes toward the object the subject wants to look at. When looking at a close object (e.g. one’s nose), the eyes move inward (converge), while when looking at something farther away, they move away from each other.
Accommodation is defined as the contraction of ciliary muscles around the crystalline to form a sharp image onto the retina. This process is used to change the “focus” of the eyes, adapting it to the distance of the object one is looking at.
In natural viewing conditions, accommodation and convergence are coupled: an object that is nearby will require the eyes to converge and the crystalline to get rounder to put it into focus, the opposite will happen with an object farther away. However, because current headset technology is monofocal, these mechanisms are decorrelated in VR viewing. Eyes still converge in accordance with the virtual distance of the object, recreated by image disparities between the two eyes, but the accommodation distance remains always the same, corresponding to the distance to the virtual display screen (Frey et al., 2014; Kramida, 2016; Mon-Williams & Wann, 1998; Williams & Parrish, 1990).
Different studies have shown that visual fatigue following VR exposure can lead to an increase in the minimal distance of accommodation (Mohamed Elias et al., 2019; Szpak et al., 2019; Yoon et al., 2020), and to a lesser extent, an increase of the minimal distance of convergence (Mohamed Elias et al., 2019; Yoon et al., 2020).
More generally, the occurrence of visual symptoms has been reported to be as high as 60% in a sample observed by Mon-Williams and colleagues (Mon-Williams et al., 1993). The systematic presence of visual fatigue after VR exposure with HMD has been confirmed by a recent meta-analysis (Yuan et al., 2018) . Interestingly, the authors found a significant effect even when excluding studies performed before the year 2000 using older HMD systems. Moreover, visual fatigue seems one of the most difficult symptoms to avoid, as it has been shown that even after five immersion sessions, when other symptoms were reduced, probably due to habituation, eye strain was still the most reported symptom after each of the immersion sessions (Lampton et al., 2000).
Of note, these results have been obtained in young populations (19-39 y.o.), usually exposed to a short (all studies used scenarios not longer than 30 minutes) single (with the exclusion of the study by Lampton and colleagues (2000)) VR session. Thus, the effect on visual health and sight of longer or repeated exposures to VR is unknown, as it is unknown the effect that VR exposure may have on the sight of an older population. The main aim of the current study was thus to investigate the effect of repeated, longer exposures to VR, aimed at training piloting procedure, on the sight, and in particular on the near point of accommodation and the near point of convergence, of pilots within an age-range usually not included in VR study (40 to 60 years old).
Other cybersickness symptoms
Apart from visual symptoms, the other symptoms pertaining to cybersickness should be inquired to ensure the well-being of pilots exposed to VR training.
Concerning disorientation, it has been suggested that a predominance of disorientation symptoms over nausea-related symptoms is what differentiates cybersickness from simulator sickness and motion sickness (H. K. Kim et al., 2018; Y. Y. Kim et al., 2005; K. M. Stanney et al., 1997). One recent meta-analysis of VR studies using HMD reports that the disorientation subscale of the SSQ is the one showing the highest average value for post-exposure assessments (Saredakis et al., 2020).
As for nausea, a recent study using state-of-the-art technology and three out-of-the-shelf VR games showed that 43 out of 195 subjects (22%) somewhat or strongly agreed with the sentence “the experience was nauseating” (with 5% that strongly agreed) (Stone Iii, 2017). Other authors report a similar estimate of 25% of subjects reporting mild or severe nausea symptoms, using HMD and a static-environment visual stimulation(Moss et al., 2008). A slightly smaller proportion of 20% of subjects reported having nausea-related symptoms in one of the first studies concerning HMD VR (Mon-Williams et al., 1993). Another study, using two intentionally provocative roller-coaster rides simulation, found that all subjects (12 out of 12) reported being at least mildly nauseated, with 8 subjects quitting the immersion across the two rides (Davis et al., 2015).
Similar to the literature about visual symptoms, the studies reported in this paragraph used mainly single and short VR exposure and included only young adults (19 to 39 years old). The second aim of the current study is thus to assess the well-being of pilots drawn from an older population (40 to 60 years old) exposed to longer and repeated VR sessions in terms of cybersickness symptoms.