Even "incidental" exposure to advertising on commercial websites may have a significant impact on consumers, new research has revealed.

A study by US academics due to be published in the June issue of the Journal of Consumer Research found that website banner ads influence surfers even if they are not aware of having seen them.

"Regardless of measured click-through rates, banner ads may still create a favourable attitude towards the ad due to repeated exposure," wtote Xiang Fang (Oklahoma State University), Surendra Singh (University of Kansas) and Rohini Ahluwalia (University of Minnesota).

"Effects of mere exposure are expected to grow in a marketplace where consumer attention is often focused elsewhere."

The researchers investigated whether "mere exposure effect", a condition in which people develop a positive perception of stimuli not presented to them on a noticeable level, was also applicable to incidental advertising.

In a series of experiments, they discovered that even if people could not recall the content of the ad, repeated exposure led to familiarity, which then led to positive feelings.

"Our research could have important theoretical and practical implications. Theoretically, it enhances our understanding of the process underlying the mere exposure effect," said the researchers.

"Practically, it provides some useful guidelines for advertisers to develop more accurate measures of banner ad effectiveness."

Participants had more positive evaluations towards the target banner ad as exposure frequency increased. Surprisingly, participants also showed high levels of tolerance for banner ads on which they were not directly focused.

According to the researchers, common wear-out effects were not apparent even after 20 exposures.

"Our results suggest that the fluency resulting from frequent passive exposure, and the consequent spontaneous affective reaction, provide a crucial link between exposure and positive impressions," wrote the authors.

"Such spontaneous affects influenced evaluative judgments through a more complex process, likely by colouring the interpretation of the fluency experience and the nature of resulting meta-cognitions relating fluency with liking."