Negative Priming: Why Stock Photos Reduce Conversions

For many years, Jakob Nielsen has listed  “Anything that looks like an ad” as one of the top 10 mistakes in web design. But he and others aware of ‘Banner Blindness’ might be surprised by the significant negative effects of stock photos of people in the Behavioural Insights Team Update Report. In two large trials with thousands of visitors to government web sites, stock photos of people had negative effects on goals. The study authors were surprised by the effects, but we believe that people unconsciously avoid looking at the photos- and that this can be explained by psychological phenomena of attention and priming. Even without considering the psychological underpinnings, our message: use stock photos of people with great care.

Organ Donation study images

Organ Donation study images

The first example is the Behaviour Insight Team’s hugely successful Organ Donation study. In this 5 week trial, 8 design variants of a message to encourage registering for organ donation were presented to over 1 million people (approx. 135,000 saw each variant). Variants 2, 3 and 4 shown below showed a social norm message “Every day thousands of people who see this page decide to register” – only variant 3 included a stock photo image of people.

The social norms message had a positive effect, but in Variant 3, when the picture was displayed with the message, it not only counteracted the beneficial effect of the message, it had a significant negative effect, as shown in the orange bar below. Apparently, this result was the opposite of what the team expected.

Organ donation register sign-ups resulting from different messages

In the second trial,  the culprit was a carousel of images on the Stoptober website, where the goal was to increase sign-ups.  Variant 11, in orange below, increased sign-ups the most. It displayed a testimonial and a benefits message, without a carousel of images. The team found that all of the variants with a carousel had a negative effect – (for example, v8, v9, v24, v20 and so on) consistently reducing sign-ups by 0.5 percent compared to the Control.

“By removing the carousel while the campaign was still live, Public Health England and BIT were able to add 3,000 registrations to the campaign”  

Chart of results showing control

People May Avoid Looking at Stock Photos of Faces

We think that the images have negative effects in these BIT studies because fewer people actually looked at the image variants.  In usability tests, we often hear participants say “I didn’t even see that” about images.

Results from a large eye-tracking and quantitative study in 2009 support this idea that people don’t see the images.  In the Faces on Web Pages study, eye tracking participants appeared to avoid looking at a message accompanied by an image of a face, and all study participants were significantly less likely to click to successfully complete the task in the face-image condition. As in the BIT studies above, the authors also say they were surprised by the results.                

“We believe this may largely be due to the over-exposure many web users have had to faces in ads on the web. Some users may have simply learned to “tune out” faces.” from ‘Are People Drawn to Faces on Web Pages’ – CHI 2009

Inattentional Blindness and Negative Priming 

Inattentional blindness is the phenomenon of not seeing something unexpected that is in plain sight. Many know of it through Chabris and Simon’s famous ‘Invisible Gorilla’ experiment. A later study of inattentional blindness and priming published in the Journal of Vision, takes it further. It shows that negative priming (actively avoiding responding in a particular situation) appears to increase inattentional blindness later. So actively avoiding looking at ads on web pages in the past can cause people to avoid looking at stock photos – even on government web sites.

“Thus, attentional decisions not only modulate perception in the moment; they also continue to govern the contents of awareness down the line” –  Journal of Vision

These theories and results for negative priming and inattentional blindness lead us to suggest that web visitors are primed to ignore  – to be blind to – anything that looks even vaguely like an ad on non-retail sites. They’ve been negatively primed by previous experiences with ads. Stock images of people, in particular, will invoke this response. If you want people to convert, or click on a link on a government site,  stock photos of faces may harm rather than help.

Sources and additional studies: 

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