Against a background of black-tea aroma, noticing a change to lemon aroma may take a little longer. A 2021 study delivered either black-tea odor or odorless air, briefly switched to lemon or almond odor, and measured how quickly people responded.
The result was that responses to lemon were slower against a tea background, while the same delay was not clearly observed for almond. The researchers examined the hypothesis that familiar odor combinations are treated as a single unit, making changes in individual odors harder to notice.
Does a familiar combination change what we notice?
With familiar combinations such as lemon tea, we may perceive the aroma of a single drink rather than tea and lemon separately. This study asked whether that grouping also relates to the speed at which people detect a change in odor.
Almond odor was chosen for comparison because tea and lemon were expected to be a familiar combination, whereas tea and almond were expected to be less familiar. However, familiarity and how well the odors fit together as food were treated as separate judgments.
Replacing the tea stream with another odor for 300 milliseconds
Forty-nine people aged 20–28 in Japan participated. After excluding participants who could not perceive the target odors and other exclusions, reaction-time analyses included 44 people, 22 men and 22 women.
The background delivered to the nose was either odor from a commercial unsweetened black-tea beverage or odorless air. Food-grade flavorings were used for lemon and almond, diluted to approximately match their intensities.
In the tea condition, black-tea odor was presented for about 10 seconds per trial, with a switch to lemon or almond for just 300 milliseconds, or 0.3 seconds, during that period. A key feature was that the stream was briefly replaced, rather than flavoring being mixed into the tea odor simultaneously.
Participants held their breath during a cue and pressed a button as quickly as possible when they noticed a change in the odor environment. The procedure was designed to reduce breathing timing and the apparatus’s switching noise as potential cues. They experienced the four combinations of two backgrounds and two targets in varied order across two sets of 80 trials, for 160 trials in total.
A tea background delayed lemon detection
Reaction times to lemon odor were significantly longer when switching from tea than when switching from odorless air. For almond, the background difference was not clear. The interaction indicating that the background effect differed by target odor was also significant.
When the odors were rated separately, tea was judged weaker than lemon or almond, and lemon and almond did not differ significantly in intensity. However, these ratings were made individually after the main task. The researchers did not measure how intense the briefly presented lemon seemed at that moment against the tea background.
Nor did the results show that lemon was always harder to detect than almond. Reaction times for the two targets did not differ significantly within either background. The central finding was the effect of the background on responses to lemon.
Familiarity differed, but congruency did not clearly differ
A subset of the reaction-time participants also evaluated the odor combinations. Twenty-eight took part; after excluding three who could not perceive the tea, 25 were included in the analysis.
Because the apparatus could not deliver two odors simultaneously, it alternated 600 milliseconds of tea with 200 milliseconds of lemon or almond to produce a presentation perceived as a combination. Participants then rated how familiar the combination was and how well it fit together as food.
Tea and lemon were rated as more familiar than tea and almond. However, the combinations did not differ significantly in congruency. A well-known combination and one that seems to go well together were not the same measure.
For the individual odors, lemon received higher pleasantness and liking ratings, and pleasantness and liking were strongly correlated for both odors. Differences in individual-odor familiarity and perceived edibility were not clear. The researchers assessed these properties of the odors themselves to help interpret detection speed.
Experience-based grouping is one plausible explanation
The authors concluded that the findings were consistent with the hypothesis that boundaries between individual odors become less distinct in familiar combinations. Everyday food experience may influence how aromas are treated as a single unit.
However, participants’ actual frequency of drinking lemon tea was not measured, and this was not a training experiment that increased their experience of drinking it. Other explanations remain possible, including tea and lemon compounds acting on similar receptors or the background reducing the perceived intensity of lemon. The study did not measure brain activity or receptor responses.
The authors call for research on other food combinations, participants from different food cultures, and relationships with individual drinking frequency. Holding one’s breath to detect a brief switch also differs from actually drinking and tasting.
Summary
With black-tea odor in the background, responses to a briefly presented lemon odor were slower than with an odorless background. The same background effect was not clear for almond, and tea and lemon were rated as the more familiar combination.
Well-known aromas may be perceived as a whole rather than as individual elements. By examining the time it takes to notice a change, this study explored that possibility and offered a starting point for further tests linking experience with odor perception.
Kirin Holdings provided the main research funding, and coauthor Ayaka Hoshi was affiliated with the company at the time. Tatsu Kobayakawa disclosed research funding from the company, while Naomi Gotow declared no competing interests. The study also received JSPS KAKENHI support. The paper states that the company did not control interpretation of the results, writing, or publication.
References
Gotow N, Hoshi A, Kobayakawa T. Background stimulus delays detection of target stimulus in a familiar odor–odor combination. Scientific Reports. 2021;11:11987. Original article.
