Trigeminal

Impression: The feeling (illusion) of temperature without the temperature physically changing.

Event: Experimental and demos/interactivity sessions at research conferences. 

Receiver: Participants that are invited to a temperature-controlled laboratory room and donned a VR headset with an olfactory display. 

Sensory elements: An olfactory (scent) interface affixed to the VR headset, as shown in Figure 3.17, delivers different scents alongside two scenes: scene (a) a patch of grass in a desert oasis (hot) and scene (b) a flower patch on an icy mountain (cold). The researchers evaluated the participants immersion into the scene by testing three different scents: (1) cooling: a eucalyptol scent, (2) warming: a capsaicin scent; and (3) baseline: alcohol (solvent). 

• In the additional demonstration experience, users started inside a cozy, heated cabin in a wooded, winter landscape, viewed through a VR headset. To enhance realism, the wearable device triggered warm sensations by intermittently atomizing a cayenne pepper tincture solution (rich in capsaicin) every 6 seconds. This mimics the warmth of the cabin's furnace. Suddenly, mountain winds blow open the door, cutting off power and extinguishing the furnace. The device then switches to atomizing eucalyptol every 12 seconds, simulating the chill from the now unheated cabin. The user needs to restore the cabin’s power and heat to combat this cold.

• Venturing outside, the drop in temperature prompts the device to atomize eucalyptol more frequently at 6-second intervals, intensifying the cold sensation. Upon discovering a backup generator, the user activates it, and it begins to emit heat and a smoky, rubbery scent. The device responds by adding bursts of warm scents every 12 seconds and a distinct rubbery fuel-like odour as the generator runs, increasing the immersion by simulating both the smell and the tactile sensation of heat.

• Once power is restored, the user returns to the cabin, where the furnace has been reignited. The device gradually reduces the emission of eucalyptol and resumes more frequent bursts of capsaicin, recreating the warming environment inside the cabin. This sequence not only enhances the VR experience with scents but also effectively integrates temperature sensations to elevate the realism of traditional smell displays.

Concepts: Semantic congruency and sensory corresponding cues, alongside temporal synchrony are key elements to enhance realism and immersion in a virtual environment augmented through temperature sensations elicited through scent. This research has shown the power of creating temperature illusions through scent. Moreover, works inspired by this work (i.e. Maki Ueda’s installation Smells for the Paris Agreement), showed that visuals are not needed to produce a strong effect, thus, giving more weight and attention to the sense of smell.

Enabling technology: A thermal display that does not utilise heat or cold but instead creates an illusion of temperature using scent. The warmth of a desert is achieved by emitting a capsaicin-based scent and (b) the coolness of an icy mountain by emitting eucalyptol. In addition to these chemical compounds, a key enabling technology to deliver capsaicin (and compounds with high vapor pressures more broadly) is the vibrating mesh transducer, a thin metal sheet with holes that act like tiny pumps when it vibrates, which in turn allows low-viscosity liquids to be aerosolized. Then, the compound associated to the temperature sensation desired simply needs to be routinely aerosolized to produce the illusion of temperature.