The smell of coffee arrives as you watch a video of coffee being made. Creating this experience takes both a device that releases the scent at the right moment in the scene and a way of making that scent come across as recognizably coffee-like.
In a study published online in December 2024, Chuhong Wang and colleagues developed a device that switches between four scents in time with video and sound, and had 28 people try it. The aim was to build a mechanism for controlled scent delivery from a consistent direction and investigate how people perceived it during a viewing experience. The paper appeared in a 2025 journal issue.
Moving the bottles to a common outlet
Rather than being worn on the body, the device is placed near the viewer. Commercial spray bottles are arranged on a rail, and a motor moves the bottles to bring the desired scent to a common spraying position. An electromagnetic pressing mechanism then presses the spray head, and a fan carries the scent toward the viewer.
Four bottles contained commercially available, water-soluble fragrance materials corresponding to coffee, flowers, chocolate, and strawberry. A fifth bottle held water to flush the shared delivery pathway. The design switches between scents one at a time; it does not mix all four simultaneously to create a new scent.
When scent generators are placed in different locations, each scent may arrive from a different direction. This device uses one pressing mechanism, a fan, and a shared tube so that every scent arrives from the same direction. The aim is to spare viewers from having to turn their heads to find the scent.
Starting scent delivery 10 seconds before the image
After a spray was released, it took about 10 seconds for the measured concentration of volatile compounds to reach its maximum. Assuming that the concentration peak corresponded to the moment of strongest perceived intensity, the researchers set the device to begin releasing the scent 10 seconds before its subject appeared on screen.
This setting was not based on confirmation that everyone perceived the same intensity after 10 seconds. Instead, the device measurements served as a guide for presenting the scent in advance to align it with the video.
The experience used a roughly three-minute video with sound. It moved from a coffee shop to a garden with flowers, then to a scene of making a cake with chocolate and strawberries. In the final scene, the device released chocolate scent before switching to strawberry. Gaps between scenes also allowed time for switching.
Which scents did the 28 participants select?
The participants were 19 men and 9 women, most of them under 34 and recruited from a university community, including students. After taking an identification test using 12 odors, they watched the video from about 50 centimeters away from the device.
While watching, they selected what they smelled in each scene from coffee, flowers, chocolate, strawberry, and no scent, and rated its intensity on a 10-point scale. In all, 21 of the 28 participants correctly selected at least three of the four scents.
Flowers and chocolate were easier to select, while coffee remained challenging. According to the researchers, the coffee fragrance used had a sweet, vanilla-like character. In their post-experience responses, 12 participants also said the coffee scent was too sweet.
Even when the device correctly selects the “coffee bottle,” its contents may not closely match the smell of coffee that participants expect. Electronically selecting a scent and determining what people perceive that scent to be were separate challenges requiring adjustment.
The matching images and answer choices were present together in this test, and there was no comparison with a condition in which no scent was released. Correct answers alone therefore do not establish that participants identified the scents without relying on visual cues.
Enjoyment ratings and usability challenges
Ratings after the experience were generally high on the 10-point scales: comfort averaged about 8.4, and immersion and interest also averaged about 8.4. Many participants viewed the scented experience positively, but these were post-experience impressions. The scores did not demonstrate greater immersion than an unscented video through a comparison with a control condition.
Participants also identified specific areas for improvement. Some found the floral scent too strong, while others raised concerns about the device’s size and appearance, lingering scent in the room, and difficulty setting it up. Six said the motor that moved the bottles was too loud.
All fragrance materials were diluted with water at the same ratio in this study. However, equal dilution does not necessarily produce the same release of compounds or the same perceived intensity. The authors suggest that, beyond letting users choose preferred scents, a system should check each person’s perception before use and allow intensity adjustments.
Conclusion
This study demonstrated a device that moves bottles to spray from a common position, delivering multiple scents in sequence alongside video and sound. User evaluations revealed both positive reactions to the scented experience and areas for improvement, including fragrance selection, intensity, and operating noise.
The authors’ next priorities include choosing fragrance materials that represent scenes well, adjusting the amount sprayed, and making the device quieter. Their outlook also includes evaluation with a broader range of users and a system that uses AI to match scents to scenes. In technology that adds scent to video, designs that control the timing and direction of release need to be combined with evaluation of how people interpret the odors.
References
Wang, C., Daulton, E., & Covington, J. A. (published online in 2024; 2025 journal issue). Multi-scent olfactory display with visual and sound interaction. International Journal of Human-Computer Studies, 197, 103421. DOI: 10.1016/j.ijhcs.2024.103421 / Full original article.
The authors declare no financial competing interests or personal relationships that could have influenced the study. Original article: © 2024 The Author(s), CC BY 4.0.
