There are several main areas that scent-focused XR is tasked with addressing, the first of which being position tracking. In order to trigger appropriate smells at times that correspond with the storytelling in a virtual experience, it is important that the system is able to track where a user is in this digital environment, so that as they come upon scent-triggering elements, smell technologies are able to react in a way that corresponds to what is seen. Next is the production of odorants, which is ideally done through the establishment of a finite set of chemicals which can be mixed in order to produce a wide range of smells. Some researchers have compared this to the way “colors are mixed in a printer” (Eskeland). Storing these odors is also a big opportunity for innovation in the VR space. It is very important the interface be as non-obtrusive as possible, and still serve as an effective storage method for scents of different potencies, saturations, and odors. Last, and one of the most important pieces to this, is the delivery method: getting the smells to be perceived by the user in a way that takes into account habituation. Habituation is the desensitization to a particular stimulus after continual exposure to that stimulus; in other words, an odor will be sensed at a much more sensitive level when it is first introduced versus 30 minutes into the experience.
Scent-focused XR technologies began in the late 1990s with Myron Krueger, who was actually the scientist that coined the term “artificial reality”. He received a grant from the Defense Advanced Research Projects Agency to develop smells to be used in VR medical training simulations, hoping to add what he referred to as “telesmell” to the battlefield telemedicine (MIT Technology Review). His team began work on a headset that looked, at least structurally, like the equivalent of the standard head-mounted displays used for visual experiences, but for olfactory sensation. They did their own research into past attempts to curate scents and feed them into users’ sensory channels. They found that most odorant storage solutions “require that the compound is vaporized using heat or electrostatic methods” (Eskeland). There were also strides made in terms of developing a delivery mechanism, which consisted of an air flow to the user’s nose, in addition to a contraption to clean air input in order to completely change the scent being delivered, if needed. Though this research got very little attention outside of the military research space (since that was the application the team was funded to design for), it still set down the blueprint for olfactory VR research going forward. People in the XR world now knew that it was a viable area of focus in the field, and some saw its potential beyond the battlefield.
Using the work of Krueger’s team as a jumping-off point, Jas Brooks at the University of Chicago began researching the capabilities of stimulating the trigeminal nerve in the nose to simulate temperature change. Their goal was to trigger a haptic response- the sensation of temperature change through touch- through users’ sense of smell as opposed to complex, immensely power-consuming electronic components that were being used at the time, which had proven themselves ineffective relative to their high price point. The trigeminal nerve is primarily responsible for providing sensation to the face. Brooks’ team created a device that stimulates this region by pumping “thermal” scents through a vibrating mesh atomizer, which is essentially a filter that in turn emits the odorant as a fine spray (Brooks). To create a sensation of warmth, the device sprayed cayenne pepper tincture solution, paired with a visual experience that corresponded: a fire crackling inside the cabin of the participants’ VR world. Midway through the experience, the cabin door would burst open, triggering the release of eucalyptol from the headpiece that mimicked the sudden gust of cold air coming in from outside. The team recorded what research participants believed the temperature to be with and without the olfactory stimulants. Ultimately, they found that the effect of trigeminal stimulants on the reported temperature was statistically significant. People reported temperatures to be higher when their VR experience was paired with an olfactory sensation, though they weren’t actually perceiving any haptic feedback. This was a huge moment for olfactory VR- it meant that our sense of smell, paired with visuals-focused VR could actually trigger touch-based sensations as well, which is essential in creating immersive experiences.