What if ad makers could tap directly into the part of the brain that’s in charge of deciding if a consumer wants to buy your product? No guesses—just science. Sounds like fiction, right?

Today, companies are turning to neuromarketing, a field in which marketers borrow neuroscience tactics to measure a consumer’s brain activity in response to certain images or messages, and craft campaigns accordingly. The best approaches ignore so-called stated preferences, or what consumers say they like, in favor of revealed preferences—the preferences, sometimes unconscious, that consumers can’t hide.

This Is Your Brain on Ads

Neuromarketers use several methods to assess how people feel about messages, ideas, images, and slogans. These approaches include traditional surveys, implicit-association tests (which measure how strongly people associate two concepts), and biometric scans. The two most successful methods, however, incorporate specialized technology to dig a little deeper into what’s actually going on in the brain.

For example, functional magnetic resonance imaging (fMRI) is a technique that uses MRI technology to measure the blood-oxygen levels in the brain, producing images that resemble a heat-sensor photograph. Scientists can see at a glance where the “warm” regions are and, therefore, where the most activity is concentrated. Based on that information, they can draw conclusions about what a consumer is thinking and feeling. Electroencephalography (EEG), another approach, uses electrodes placed strategically along the scalp to record the electrical signals brainwaves produce, allowing marketers to conduct a similar kind of analysis.

Recent studies have shown that, compared to surveys and more traditional methods of assessing consumer preferences, EEG and fMRI data from experiments with small control groups (fewer than 30 people) are better at predicting how the masses will respond to an ad. More importantly, however, tools such as EEG and fMRI map not what people think their reactions are (or the reactions they feel comfortable expressing to researchers), but their actual reactions, which often occur at the subconscious level.

A study by researchers who were affiliated with the Stanford Graduate School of Business and the California Institute of Technology, published in 2007, provides a classic example of how neuroimaging technology can uncover revealed preferences. The team performed fMRI scans on people while they tasted wines that they believed had come from different places and carried different price tags, but were in fact the exact same wines.

The brain scans showed that the subjects not only believed the more “expensive” wines were of higher quality, they also genuinely preferred drinking them. In other words, people’s beliefs easily fooled their own senses.

Similar tests can help determine how effective a given ad campaign may be, or how people might react to a specific product. In one experiment, for example, Hyundai equipped participants with electrode-studded EEG caps and asked them to stare at specific parts of a model car. Technicians monitored the electrical activity in the participants’ brains and stored the resulting data on a hard drive that subjects wore around their waists. After examining the data, the company indicated it would fine-tune the exterior of the model to fit consumers’ preferences.

Similarly, when PayPal (then part of eBay) launched a campaign to refresh the brand’s identity, it turned to neuromarketing company NeuroFocus to track the subconscious brain activity of a panel of consumers. An EEG revealed that words like “fast” resonated much more with consumers than words like “safe,” and that speed triggered positive feelings in frequent users. PayPal revamped its global image to reflect these findings, with campaigns that showed people enjoying the time they saved with faster payments. After updating the brand’s identity across the company’s email and web pages, response and click-through rates increased up to 400 percent.

Neuromarketing works for one reason: People don’t always know what they want or what exactly they like about something. What’s more, brains don’t lie, and they don’t get embarrassed. Sometimes, if you want to know whether an ad campaign or messaging plan will resonate, it’s best to go straight to the source.