From the sweet wafting of vanilla on Main Street, USA to the slow burning of wood in Spaceship Earth and the barrage of ocean breeze and orange groves in the various iterations of Soarin, Disney’s smell machines rely on some relatively simple technology to enhance the sensory experience of their park and make your memories that much stronger.
How do Disney’s scent machines work?
Put simply, Disney’s smellitizers involve positioning a scented substance (whether this is actual popcorn or an artificial scent) between a source of strong airflow (fan or pressurized air) and the audience, then turning the airflow on and off so it blows across the substance and toward the audience. This process works because of how chemicals become airborne and how we smell, explained below.
From the patent for the Soarin’ smellitizer system seen in the image above, a nozzle 62 may be located in proximity to the fan 55. The nozzle in FIG. 4 is connected to a reservoir 70 located upstream of the nozzle. Compressed air is supplied through a compressed air inlet 65. The flowing air draws a scent material 67 from the scent reservoir 70 and delivers it through the nozzle 62 to the region of the fan. The scented air then moves through the air plenum 58, which directs it out of the canopy and downward over the passenger.
The science behind the magic
Smells are caused by substances that are sufficiently volatile. Volatility doesn’t mean that the substances are evil or mean like Scar or Maleficent but rather, a volatile substance has a tendency to vaporize, or turn into a gaseous form. We are only able to smell things when the molecules that make them up are in gaseous form because only gases can reach the space in our skull where we detect smells. But how do substances that are not gases to begin with transform into gases?
Typically, substances transition from liquid into gas form, like when we boil liquid water and it turns into water vapor. Similarly, scented candles distribute scent by heating solid wax first into a liquid and then into a gas. But liquids are difficult to control in machinery, thus smellitizers are not likely to always use substances in liquid form. (Yes the image from the patent may look like liquid, but this has not been confirmed. Furthermore, having a different liquid container for each scent on Soarin’ may be inefficient compared to the methods described below)
Because we are still able to smell the scents of things like candles, soaps, and solid air fresheners even when they are in seemingly solid form, is there another way that smellitizers could achieve their desired effect? Yes! They could either rely on containers of chemicals already in gaseous form or on a process of transforming a solid into a gas called sublimation.
Sublimation requires very special conditions depending on the material in order for the molecules in a solid to have enough energy to become a gas. Heating a solid air freshener is one way to cause sublimation and distribute scent but I think it is unlikely that Disney uses nearly constant heat in all of its smellitizers if it can be avoided because of the high cost of supplying enough energy for such a process. Furthermore, regular life experience seems to indicate that solid air fresheners work pretty effectively even when not in a heated location. Thus, alternative materials or conditions need to be used to make a solid substance in a smellitizer smell.
The most likely explanation is that blowing cool air over the scented substance (typically composed of volatile organic compounds) with a powerful fan or compressed air tank lowers the air pressure above the scented substance by blowing away the molecules that were present before. The same process is at work when wind blowing over a puddle causes the puddle to evaporate more quickly. With fewer molecules present above the scented substance or puddle, more molecules can escape into the air. More molecules turning into gas form results in a higher likelihood that we will detect a smell.
How do we smell?
Chemicals from smell-producing objects travel through the air, into our nostrils (or through our mouth and to the back our throat), through our nasal cavity until they reach a section of the nasal cavity called the olfactory epithelium.
The olfactory epithelium is a membrane covered in mucus that traps the chemicals for smell and is littered with 40 million olfactory neurons. Each of these neurons has special proteins in their membranes which function like locks that are only opened by the proper smell molecule key.
After the molecule unlocks all the receptors that it can, the neurons with those receptors activate and send a signal to a different part of the sensory nervous system called the olfactory bulb, which is just a bundle of neurons.
In addition to sending the signal from the olfactory bulb straight to the olfactory cortex (where higher-order processing occurs), the signal is sent to both the amygdala, which is responsible for emotions, and the hippocampus, which is necessary for memory formation.
Why is smell so powerful for triggering memories and emotions?
The several neurons activated by a smell’s molecules are usually arranged in a particular spatial pattern in the olfactory bulb that is gradually (through repetition) associated with the object that caused the smell. This recognition is how a memory for a smell is formed, just like the activation patterns associated with an image of Mickey Mouse’s face in the visual cortex or Mickey’s voice in the auditory cortex are paired together over time.
Because we have more unique types of receptors for smells (at least 350!) than we do for sight, our memories for smells can be much more specific and also require less complicated integration of sensory information. This specificity may be one of the reasons why we can recall a more specific set of memories from a smell than from just an image (such as a photo of a perfume bottle or the word “rose” instead of the smell associated with each).
Additionally, there are fewer steps involved in the pattern recognition of smells (through the olfactory bulb then to the cortex) than the pattern recognition of sights or sounds (which must first go through a traffic control center called the thalamus). The sensory pathways for smell are much more integrated with the amygdala and hippocampus than other sensory pathways, which likely served our ancestors well in their survival: having a better memory for smells of predators and dangerous foods would prevent death.
Furthermore, smell memories are some of the best-preserved over time. If the first time a memory for a scent is formed occurs during childhood, positive emotions associated with nostalgia can make that memory even more powerful. This may explain why the faintest smell of a churro can bring me back to walking along the Rivers of America in New Orleans Square and why I burst into tears when the Disneyland 60th Anniversary fireworks were accompanied by gingerbread scented “snow” that reminded me of baking gingersnaps with my grandmother.
The importance of precision
What’s so special about Disney’s smellitizers is that the smells are timed precisely, released relatively discreetly and directly, dissipate quickly and can be used repeatedly for around 80 to 100 showings a day per theater. Imagine not smelling the dirt from Mt. Kilimanjaro until the Paris scene of Soarin’ – doesn’t really make you feel like you are transported to either locale, does it?
These kind of problems plagued a 1950s-era technology called Smell-O-Vision. Originally used in movie theaters, Smell-O-Vision quickly declined in popularity because the mechanism detracted from, rather than added to, the movie-watching experience. The fans used to dissipate the scents were loud, covering up the music and dialogue, and the scents took too long to reach audience noses so that the smells were not synced properly with the film.
Combining knowledge from chemistry, engineering, and neuroscience, Disney’s smellitizers make riding their attractions much more magical and realistic. From classics like the Haunted Mansion and Pirates of the Caribbean, to Soarin’ and Flight of Passage, the manufactured smells are powerful for helping families remember their vacation for years to come.
What scent (Disney or non-Disney) is the most powerful for you? For me, it’s the smell of oranges from Soarin’ Over California and the smell of fresh-cut grass from home.
Arshamian A, Iannilli E, Gerber JC, Willander J, Persson J, Seo H-S, Hummel T, & Larsson M. The functional neuroanatomy of odor evoked autobiographical memories cued by odors and words. Neuropsychologia 51 (2013), 123-131.