Priming is one of the most significant—yet least visible—mechanisms explaining why OOH and DOOH often generate greater impact than “last-click” models reveal. When people first encounter a message in the public sphere, their brains are “pre-set” to notice it when that same message reappears on their mobile, in social media, or on a website. The effect is manifested as improved performance in other channels, not necessarily as a direct line item in the OOH report.

JCDecaux, in several projects with Lumen Research, has demonstrated how this priming effect works in practice and why it is becoming increasingly vital in a cookieless future.

What is priming in a marketing context?

In psychology, priming describes how an earlier exposure influences how we interpret and react to later stimuli, often without us being conscious of it. In marketing, this means:

• An initial contact with a brand (e.g., an OOH exposure) makes the brain faster and more inclined to notice, recognize, and react to the same brand later.

• The effect is not just about “liking” but primarily about mental availability—the brand feels familiar and is easier to choose when the need arises.

• When this first contact occurs through out-of-home advertising situated in people’s natural, everyday environment, it creates a visual memory that other channels can build upon.

JCDecaux x Lumen: Proof that OOH primes digital channels

JCDecaux UK commissioned Lumen Research to conduct an attention study titled “Primed and ready for the cookieless future” to test a clear hypothesis: if you expose people to a message on digital out-of-home (DOOH) first, does it increase their attention to the same message online? The study shows:

• Exposure in DOOH increased the likelihood of noticing subsequent digital ads with the same creative execution.

• The combination of OOH/DOOH and digital advertising can create an amplifying effect, where “2+2 equals 5,” compared to showing the same digital ads without visual priming. This is a concept further detailed by Mike Follett, MD of Lumen Research, for The Media Leader.

• The effect stems from visual recognition, not individual-based tracking. This makes priming a powerful tool in a world where third-party cookies are becoming less reliable due to browser blocking, stricter privacy legislation, and shifts like Google’s Privacy Sandbox.

The priming chain: From street to screen

A simplified journey looks like this:

1. First contact – Public screen: A consumer passes a DOOH screen in a transit hub and sees a brand campaign, clearly branded with a logo, color palette, and key message. The motif is registered both consciously and unconsciously.

2. Second contact – Private screen: Later that day, the person scrolls through social media or reads news online. When a banner or social ad with the same visual identity appears, it feels more relevant and is easier to notice. The Lumen study shows that this prior DOOH exposure increases the actual attention time spent on the digital ad.

3. Third contact – Search or retail: When the need arises and the consumer searches for the product, clicks an offer, or stands in front of the shelf, the brand is “top of mind.” This increases the likelihood that that specific brand is chosen.

Priming in a world without third-party cookies

As browsers like Safari and Firefox have long blocked third-party cookies by default, and Google moves toward more privacy-centric solutions in Chrome, the logic that long dominated digital advertising—”follow the person”—is becoming more expensive and less reliable. JCDecaux and Lumen suggest an alternative logic: follow the attention, not the individual.

OOH/DOOH creates broad reach and strong visual memory without using personal data. When the same creative is mirrored in digital channels, it captures attention because it feels familiar, not because the recipient is technically tracked.

What does the priming effect mean for ROI, ROAS, and ROMI?

Because the priming effect is largely realized in other channels, OOH risks being undervalued if one only looks at its own click data. With proper analysis, however, the connections are clear:

• ROI (Return on Investment): When OOH/DOOH is in the mix, total campaign ROI often improves because more digital contacts become effective.

• ROAS (Return on Ad Spend): Priming can cause search and social campaigns to achieve higher ROAS in areas or periods where the OOH campaign is active compared to areas without OOH support. In practice, part of “digital ROAS” is actually a result of visual priming from OOH/DOOH.

• ROMI (Return on Marketing Investment): When viewing marketing as a whole (brand + performance), OOH/DOOH becomes a central investment to raise the total ROMI.

How to use the priming effect in planning and measurement

1. Plan OOH/DOOH as the first contact: Define the role of OOH/DOOH as the “priming engine” in your strategy, aiming to create mental availability and a visual memory before a digital activation. Ensure creative consistency (logos, colors, key visuals).

2. Sync public and private screens: Run DOOH and digital campaigns in parallel rather than in sequence to amplify the priming effect between public and private screens. Use DOOH networks near key purchase situations (e.g., commute routes, retail hubs) and follow up with mobile and desktop in the same geographies.

3. Measure beyond the last click: Compare ROAS in digital channels in areas with and without OOH presence. Conduct A/B or geo-split studies to isolate the extra effect contributed by OOH priming. Integrate OOH/DOOH exposure into Marketing Mix Models (MMM) to capture both attention and sales impact.

Conclusion: OOH and DOOH should rarely be judged in isolation. A smart (D)OOH strategy is one of the most effective ways to make other channels perform better. When planning your next campaign, ask yourself: How can we use OOH/DOOH to prime the audience so that every subsequent digital contact is worth more? This is where the true power of out-of-home advertising lies.