The world is a busy place. Driving down the highway, there are cars on the road you need to track. There are also other less essential things calling for your attention like bumper stickers, billboards and signs from roadside stores. The web is also dense with information. Reading the news on your browser creates a competition between the story you are reading and other advertising on the site.
When people advertise, they must be making one of two assumptions about why that advertisement will work.
One assumption is that when you put something in the world, eventually people will look at it. When they look at it, then that provides the advertiser a channel for persuasion. This view is the basis of that annoying billboard that says, "Does advertising work? Just did!"
A second assumption is that even if people don't look at the ad specifically, they may be affected by the ad. I have written in the past about the mere exposure effect. Mere exposure (initially observed by Robert Zajonc) is the idea that when you encounter something once, it makes it easier to think about in the future. We generally like things we find easy to think about. That is why you tend to like a song more the second and third times you hear it than you did the first time. With advertising, seeing a brand logo may make you like the brand better just because the logo becomes more familiar.
However, there is also a downside to seeing an ad in a busy environment. Your eyes are constantly in motion. Your visual system makes decisions about what to look at based on what you are trying to do right now. I say that your visual system is making these decisions, because you are often unaware of what drives you to look at one thing rather than another.
When you are driving, for example, you must often direct your attention to the other cars on the road. As a result, you have to pull your attention away from competing objects like billboards.
A paper by Jane Raymond, Mark Fenske and Nader Tavassoli published in Psychological Science in 2003 suggests that when you pull your attention away from an object in favor of something else, that can affect how much you like that object.
In this work, they had people look at pairs of pictures placed side-by-side. Some of the pictures were made up of small squares, while others were made up of small circles. In some parts of the experiment, people had to identify which side had the picture made up of squares. In other parts of the study, people had to identify which side had the picture made up of circles. After each response, people were shown one of the pictures and were asked how cheerful it was.
The key result from these studies is that people found the items they selected to be more cheerful than the ones that they had to ignore. That is, just picking one item over another in an unrelated task made some of the objects feel more attractive.
What does this mean for you?
Because the world is a busy place, you will always have to choose something to look at. When you browse the web, you probably try to focus on the story you are reading at that moment or the video that is playing. If there are ads at the top or sides of the page that are distracting, then you go out of your way not to look at them. By actively ignoring those ads, you may actually cause yourself to like the products being advertised less well.