Can a Picture or a Scent Make You Eat Healthier? What Neuroscience Reveals About Vending Machine Nudge
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Written by: Abigail Ayodele Agbaze (linkedin.com/in/abigail-a-0491b2196)
Edited by: Fahad Hassan Shah
Half your day has been spent attending lectures. Your stomach rumbles, reminding you it is time to eat. You promised yourself that this semester you would eat healthier and avoid the infamous freshman fifteen. But when you reach the vending machine, you are greeted by rows of tempting, unhealthy snacks. With little time before your next lecture, you grab your favourite treat without much thought. Moments later, it is gone, and so is the promise you made to yourself.
But what if the vending machine itself could encourage healthier choices? What if subtle changes in the environment could nudge you toward better options without forcing you to give up choice? A 2025 study by Casiraghi et al. explores whether visual and scent-based nudges can subtly steer you (students) toward healthier snacks and how our brains and emotions respond.
The background
The increasing prevalence of overweight and obesity among university students has become a growing public health concern, particularly in certain regions. This raises an important question: how can everyday environments be designed to support healthier eating behaviours among students? One such environment is the vending machine. Widely available across university campuses, vending machines provide quick and convenient access to snacks and beverages. As the global vending market continues to expand, its role in shaping students' food choices is becoming increasingly significant.
However, the majority of products offered in vending machines are high in sugar and low in nutrients. Studies show that a large proportion of available snacks and beverages fall into unhealthy categories, making it difficult for students to make healthier choices. Given this, an important question emerges: what strategies can effectively promote healthier food choices within vending machine environments?
One promising approach is nudge theory, which involves subtly guiding people towards a specific behaviour in a natural, predictable way, without force, bans, or financial incentives, leaving all options freely available (Thaler & Sunstein, 2008). Because nudges work with our fast, automatic decision-making processes (often referred to as "System 1"), they reduce resistance compared to more restrictive interventions such as removing unhealthy options or imposing strict guidelines.
Despite their potential, vending machines remain relatively underexplored as a setting for nudge-based interventions. Traditional strategies such as nutritional labelling or restricting unhealthy options often require conscious effort and may be perceived as controlling. This highlights the need for more subtle, less intrusive approaches, creating an opportunity to explore sensory-based nudges such as visual and olfactory (smell) cues, which may influence behaviour more automatically.
While previous research in settings such as laboratories, cafeterias, food menus, and packaging design shows that sensory cues can strongly influence food choices, often without conscious awareness, it remains unclear which sensory cue is most effective in nudging students toward healthier options. It also remains unclear whether combining different sensory cues in a vending machine setting produces a stronger effect. Theories from neuroscience and psychology suggest that combining matching sensory cues (sight and smell) can enhance attention, engage emotions, and improve cognitive processing. However, most previous studies have focused only on final observable choices—did they choose the healthy snack?—without examining the underlying processes, such as brain activity, emotional responses, and attention, that drive these decisions.
Casiraghi et al. (2025) set out to answer two key questions:
First, can visual and olfactory nudges—alone or together—encourage students to choose healthier snacks from vending machines?
Second, what hidden emotional and cognitive processes drive those choices?
To find out, the researchers adopted a consumer neuroscience approach, using electroencephalography (EEG), skin conductance, and eye-tracking to peek inside students' brains and bodies as they observed then selected snacks. This approach allowed them to go beyond surface-level choices and uncover the hidden processes that traditional methods alone cannot capture.
Method
Setting the Stage
Eighty-eight students (64 female, 24 male) from IULM University participated. All were non-smokers with no food allergies or dietary restrictions. They were not told the purpose of the study beforehand, and they did not know they would receive a free healthy snack at the end, so that reward did not influence their choices. The shelves of the lab were arranged to replicate an actual campus vending machine. Every detail—from the dimensions, product arrangement, quantity, and positioning, to the pricing—mirrored the real machine students encounter daily.
Participants were fitted with EEG sensors (on the scalp) to measure cognitive engagement and motivational behaviour, skin conductance sensors (on fingers) to measure emotional arousal and relaxation, and eye-tracking glasses to track which healthy snacks they looked at and for how long. All equipment was worn in a backpack, allowing participants to move freely and interact naturally with the vending machine.
To immerse participants in the scenario, the researcher provided a brief: "Imagine a typical university day. It's mid-afternoon, you're tired, and you're walking past a familiar vending machine. You decide to take a break and approach it."
The Experiment
Participants were randomly assigned to one of four nudge groups:
Neutral (N): Just the vending machine, no nudge
Visual (V): A nature-themed image placed at eye level beside the machine
Olfactory (O): A jasmine scent diffused into the room 30 minutes before the session
Visual + Olfactory (VO): Both the image and the scent together
To prevent scent contamination, olfactory sessions were run on separate days from visual-only sessions.
Participants were guided into a dimly lit room where only the vending machine area was illuminated. They stood in front of the machine for 10 seconds and simply looked (observation phase). Then, without a time limit, they selected a snack to buy (choice phase). During both phases, the researchers recorded data across three levels of analysis: behavioural (which snack was chosen), neurophysiological (cognitive engagement, motivational behaviour, and emotional arousal), and attentional (where and how long participants looked at healthy snacks).
After the choice phase, participants completed a short questionnaire assessing BMI, hunger level, and general health. Statistical tests confirmed that these factors were balanced across all four groups and did not influence the nudge intervention.
Before the main experiment, a separate group of 100 participants, with no food allergies or dietary restrictions, randomly rated each snack's perceived healthiness on a Likert scale, indicating agreement from 1 (strongly disagree) to 6 (strongly agree). Snacks scoring above the median were classified as Healthy (M=12.74), and those below as Unhealthy (M=7.88). This reflected students' genuine perceptions of the products.
Data from EEG and skin conductance were processed with Matlab and the EEGLab toolbox; eye-tracking data was processed with Tobii Pro Lab; and all statistical analyses were performed using R statistical software.
Results
Behavioral Level
At the behavioural level, simply looking at what students actually chose, the findings were striking. In the neutral condition, where no nudge was present, only 14% of the selected snacks were healthy. However, when a single sensory nudge was introduced, healthy choices jumped significantly: 45% in the visual condition (nature image) and 41% in the olfactory condition (jasmine scent). Contrary to the researchers' expectations, the combined condition, featuring both the nature image and the jasmine scent together, did not lead to a significant increase in healthy choices, with only 36% of the selected snacks being healthy. This suggests that a simple, single nudge can effectively steer students toward better choices, while adding more sensory cues reduces their impact.
Neurophysiological Level
The neurophysiological data, what was happening in students' brains and bodies, helped explain why. Skin conductance, which measures emotional arousal, showed that during both the observation and choice phases, the olfactory and visual conditions each resulted in lower arousal compared to the neutral control group. This means students were more relaxed when a nudge was present. Increased relaxation is linked to better dietary control because it reduces stress and anxiety, factors known to contribute to unhealthy eating habits.
However, the combined condition (VO) did not lead to lower arousal than the single nudges; adding the picture to the scent did not make students any more relaxed than the scent alone.
Across all groups, arousal was significantly higher during the choice phase than during observation, as the act of making a decision is naturally more intense.
The EEG results showed that students were generally more motivated and emotionally engaged when actually choosing a snack than when just observing. But in the combined condition (scent + picture), their motivation dropped during choice. The researchers suggest this happened because the two sensory cues together overwhelmed their brains, causing mental fatigue and withdrawal. Overall, cognitive engagement was not affected by the nudges themselves, but choosing was more engaging than just observing.
Attentional Level
Attentional data from eye-tracking revealed that when healthy snacks are placed at eye level, students look at them more. But here is the catch: this only worked when a single nudge, either the nature picture or the jasmine scent, was present. When both nudges were combined, the eye-level advantage disappeared. Students' attention patterns looked just like the neutral condition, where no nudge was present at all. This suggests that combining sensory cues does not help; rather, it may actually distract people, overwhelming their brains and competing for attention, thereby pulling attention away from healthy options instead of toward them.
The Impact
Vending machine operators and policymakers can apply several key insights from this study to design more effective health-promoting interventions.
First, sensory nudges shape our cognition and emotions when it comes to food choices. Rather than relying solely on nutritional labels or restrictive policies, interventions can work with our automatic brain processes to gently guide behaviour. To promote healthier choices, interventions should target single, specific sensory cues such as a calming scent or a nature-themed image.
Second, excessive multisensory stimulation or complex decision environments can overwhelm consumers, leading to poorer food choices. When too many sensory inputs compete for attention, cognitive load increases, motivation drops, and the intended message gets lost. This suggests that simplicity is key: a calm, uncluttered environment supports better decision-making. Nudges that facilitate relaxation and calm, like the jasmine scent used in this study, are particularly effective, as a relaxed state is known to promote more deliberate and healthy choices.
Third, specific scents that align with the store and its products can enhance the effectiveness of eye-level placement. Placing healthy items centrally at eye level is a well-established strategy, but this study shows its impact can be amplified or diminished by the surrounding sensory context. When a congruent scent is present, eye-level placement becomes even more effective in guiding consumers toward healthier choices. For vending machine operators, this means thinking beyond shelf arrangement to consider the broader sensory environment.
Ultimately, implementing these insights has implications far beyond the vending machine. By nudging young people toward healthier eating habits, we can prevent, monitor, and reduce obesity among the future adult population. Healthier populations mean reduced public health spending and the opportunity to reinvest those resources into national growth. What begins as a subtle scent or a simple image can, over time, contribute to meaningful societal change.
References
Casiraghi, C., Chiarelli, S., Gifuni, G., Fici, A., Bilucaglia, M., Jacomuzzi, A. C., Micheletto, V., Zito, M., & Russo, V. (2025). How to nudge students toward healthier snacks? Consumer neuroscience insights on multisensory nudge interventions in university vending machines. PLOS One, 20(6). https://doi.org/10.1371/journal.pone.0325804
Thaler, R.H., & Sunstein, C.R. (2008). Nudge: Improving decisions about health, wealth, and happiness. Yale University Press.
Union College. (2018). New Snack Machine. https://www.union.edu/schaffer-library/new-snack-machine
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