A scent can bring to mind a place you visited before, the moment you smell it. But when an odor serves as a cue for recalling something newly learned, does knowing that odor well also give you an advantage?
In September 2025, Mohammad Hamzeloo and colleagues at the University of Hildesheim in Germany investigated this question in three experiments. They focused on a task involving learning odor–shape pairs. Alongside odors that were already familiar, they examined what kinds of cues odors became after repeated smelling and familiarization.
Using an Odor to Select Its Paired Shape
In the experiments, participants smelled an odor while viewing a black-and-white abstract shape on a screen. They learned a pairing of “this odor with this shape” and later, when smelling the odor again, selected the corresponding shape from four alternatives. This was not a test of naming the odor itself, but a task of retrieving information associated with it.
The first experiment used eight familiar and eight less-familiar odors, selected using existing surveys and other sources. During learning, participants received feedback on whether their responses were correct, and incorrectly answered pairs were repeated until answered correctly. A 5-minute arithmetic task followed, before the actual test without feedback on the answers.
Among the 27 people included in the analysis, familiar odors led to more accurate shape selection and faster responses. However, what feels familiar differs from person to person. In the next experiment, the researchers therefore reselected odors according to each individual’s ratings.
What Counts as “Well Known” Varies from Person to Person
In the second experiment, 89 people were divided into three groups. For each person, high- and low-rated odors were selected using one of three criteria: “how familiar it is,” “how often you have smelled it before,” or “how confident you are that you can distinguish it from other odors.”
In every group, shape-selection accuracy was higher for highly rated odors. In the group asked directly about familiarity, the difference was approximately 10.7 percentage points. By contrast, in the group whose ratings concerned confidence in distinguishing odors, the difference in response speed was not statistically clear. Perceived ease of distinguishing odors and actual odor-discrimination ability also need to be kept separate here.
What Happens After Four Weeks of Familiarization?
Even if already-known odors have an advantage, that advantage might be helped by years of experience or the words an odor brings to mind. The third experiment examined whether increasing familiarity afterward would also make a difference.
The analysis included 36 people who practiced smelling odors and 21 who did not. The training group smelled 16 odors at home once a week for four weeks. This was attentive smelling practice, with participants rating eight characteristics, including familiarity, pleasantness, and intensity, each time. They did not learn any odor–shape pairs at this stage.
After completing the training, participants learned pairings of 32 odors and shapes in the laboratory. Half of the odors had been used in training; the others had not. Both sets included odors with initially high and low familiarity, making it possible to investigate separately whether smelling practice makes any odor easier to use as a cue.
The Difference Appeared for the Specific Odors Practiced
Within the training group, accuracy for initially less-familiar odors used in training was approximately 10.1 percentage points higher than for those not used. It was also approximately 9.7 percentage points higher than for less-familiar odors in the control group, which had not trained. These were differences between odors or groups under different conditions, not differences in scores before and after training.
For odors that were already familiar, however, no clear additional benefit from training was observed. For untrained odors too, there was no clear difference in performance between the training and control groups, so there was no evidence that the effect transferred to other odors. In comparisons with the control group, response speed also did not differ significantly; the benefits of training appeared particularly in accuracy.
Repeated training increased familiarity ratings, but pleasantness ratings did not change significantly. Getting to know an odor and coming to like it do not necessarily seem to progress in the same way.
How Should We Interpret the Experience of Getting to Know an Odor?
The authors consider the possibility that repeatedly paying attention to an odor makes its mental representation more accessible, making it easier to use as a cue associated with other information. Familiarity is also related, however, to how readily an odor can be put into words. The effect appeared even in experiments that did not ask participants to name odors, but the possibility that they silently verbalized them was not separated out.
The training here involved not only smelling but also thinking about and reporting perceptions. Because the control group had no alternative task involving comparable attention and time, exposure to odors cannot be fully separated from the effects of task engagement or expectations. Participants were also mainly young adults, so these results cannot be generalized to improvements in memory overall or to treatment effects.
As an example for thinking about the relationship between scent and experience, the article on perfumer Édouard Fléchier describes a habit of smelling raw materials every morning without fail. This experiment does not explain the reasons for Fléchier’s skill, but it offers a familiar point of connection when considering what repeated engagement with particular scents might mean.
Summary
When an odor acted as a memory cue, how well a person knew that odor mattered. This study also showed that even an initially less-familiar odor can, in some circumstances, make an association with newly learned information easier to retrieve after attentive familiarization.
It is also important that this change was established for the particular odors used in training. How useful an odor is as a cue may change with a person’s accumulated experience of each individual odor. Under specific experimental conditions, this study shows how that experience relates to learning and recalling new information.
References
Authors: Mohammad Hamzeloo, Luisa Bogenschütz, Ryan P. M. Hackländer, Christina Bermeitinger
Article title: Familiarity enhances the effectiveness of odors as cues in paired-associate memory
Journal: Memory & Cognition, 54(3), 959–979
First online publication and version-of-record publication: September 3, 2025 (issue: April 2026)
DOI: 10.3758/s13421-025-01790-1
Original full text: Publisher’s article page
Original study license: CC BY 4.0. The original Japanese article is an independent explanation of the research, not a republished translation of the paper. No figures or tables from the original study have been used.
