Can Flower Images Help Us Notice a Fragrance as We Get Used to It?

When a floral fragrance is present, does looking at a picture of flowers make it easier to notice? In a 2020 study, people were more likely to report an odor, and responded faster, when viewing flower images than when viewing pictures of everyday objects.

However, those differences did not persist uniformly as people continued to smell the fragrance and became accustomed to it. The research used both behavior and EEG to investigate how visual cues interact with habituation to odor.

Does a matching image change how people become accustomed to a scent?

Continued exposure to the same smell can make it progressively harder to notice. In this study, habituation refers to changes in perception or responses during a sustained odor. The team wanted to know how the benefit of semantically matching images for odor detection might change over the course of continued exposure.

The researchers used a floral-green fragrance blend called New Day. It was diluted to 5% in propylene glycol and delivered beneath the nose at a constant flow rate using a dedicated device. A screen displayed pictures of flowers or everyday objects not directly related to the fragrance.

The first experiment measured reports of noticing the odor. The second examined how brain responses to images differed in the presence and absence of odor. The design therefore considered both directions of influence: vision on smell and smell on visual processing.

25 people reported whether an odor was present during two-minute exposures

Experiment 1 involved 25 adults who met the criteria of an olfactory screening test. They completed 10 blocks of 120 seconds of odor presentation, separated by one-minute breaks with clean air.

Each block included 10 flower-image presentations and 10 everyday-object presentations, each lasting 0.5 seconds. Participants used a mouse to answer as quickly as possible whether they had noticed an odor while viewing the immediately preceding image. The fragrance was not switched on and off with the images; it flowed throughout the block.

The analysis divided the 120 seconds into five 24-second windows and compared the proportion of “odor present” responses and the time taken to respond. Although the paper calls this proportion detection sensitivity, here it is the rate of detection reports while odor is actually present, not a sensitivity measure that also accounts for false alarms on odorless trials.

Flower images increased and accelerated reports of detecting fragrance

Overall, participants reported an odor more often with flower images than with everyday-object images (p < 0.001). Responses on correctly detected trials were also faster with flower images (p = 0.002).

With either image type, however, detection-report rates decreased during continued exposure. The difference between image conditions was largest in the early window, and there was no significant difference in the final 24 seconds (p = 0.28). Habituation to the odor continued even when flower images were present.

Response times showed an overall advantage for flower images, but there was no clear evidence that this advantage changed over time. The proportion of detections and the speed of successful detections did not change in the same way.

Another 25 people had their brain waves recorded while viewing images

Experiment 2 involved a separate group of 25 adults. This time, they completed 10 blocks with odor present for 145 seconds and five clean-air blocks while EEG was recorded with 129 electrodes. They also rated odor intensity at the beginning of each block and approximately every 30 seconds afterward.

Intensity ratings were higher in odor blocks than in clean-air blocks and declined over time. Although a difference remained through the final time point, it was larger early on, confirming that participants became accustomed to the sustained odor.

The EEG analysis was aligned not to odor onset but to the moment an image appeared. The researchers focused on a negative-going potential called N400 over frontal regions, 250–400 milliseconds after image onset. It was examined as an indicator of information processing involving meaning, attention, memory, and related functions.

The odor–image combination differed in the early N400

In the initial period of odor exposure, N400 varied with the combination of odor presence and image type. When odor was present, flower images produced a greater negative response than everyday-object images. In clean air, however, the difference between flower and object images was not significant.

The same significant combination effect was not found in later time windows. This suggests that as perception of a sustained odor weakens, its influence on brain responses to images also changes.

However, in this EEG experiment, flower images accounted for 25% of presentations and everyday objects for 75%, making flowers the rarer category. N400 differences could therefore involve presentation frequency or unexpectedness as well as semantic matching between image and odor. Experiment 1 presented the two image categories equally often; this frequency imbalance concerns interpretation of Experiment 2.

How much was established about the brain regions involved?

The researchers also analyzed the likely brain sources of the recorded electrical potentials. Several regions were identified as potential sources of the early N400, including the orbitofrontal cortex, insula, cingulate cortex, and parahippocampal gyrus.

However, these sources were estimated across all conditions together. When the odor-by-image interaction was tested separately in each region, none remained significant after correction for multiple comparisons. The findings therefore cannot identify the specific location where flower images helped odor detection.

Only one fragrance was used, and the images fell into the broad categories of flowers and everyday objects. Further research is needed to determine whether the same effects occur with other odors or images that individuals associate especially strongly with them. Experiment 1, in which odor was always present throughout each block, also cannot fully separate perceptual changes from a greater tendency to answer that an odor is present.

Summary

In the presence of a floral fragrance, participants were more likely to report detecting an odor, and responded faster, when viewing flower images rather than everyday objects. However, detection-report rates declined over time, and the difference between image conditions was no longer significant during the final 24 seconds.

In a separate experiment, the N400 difference associated with the odor–image combination appeared only early in exposure. Information from the eyes and nose interacts, but that relationship does not remain constant as a fragrance continues. The study shows why habituation matters to understanding fragrance experiences.

The study was supported by Unilever. The paper states that authors T. Giesbrecht and A. Thomas were company employees at the time of the study and did not conduct the experimental design or data analysis.

Reference

Fallon N, Giesbrecht T, Thomas A, Stancak A. (2020). A Behavioral and Electrophysiological Investigation of Effects of Visual Congruence on Olfactory Sensitivity During Habituation to Prolonged Odors. Chemical Senses, 45(9). Original paper.