The idea that sex sells is as old as the hills, but its use in advertising has become increasingly unsubtle and gratuitous. There is evidence that both men and women find such advertising unethical and manipulative, so why does it continue to be used?

Perhaps men and even some women don't really mind this advertising after all, suggest Jaideep Sengupta and Darren W. Dahl.

They take a close look at previous research and find that negative views about gratuitous sex in ads are based on people having had time to consider the implications - very unlike the conditions under which people normally view ads.

"There's a strong case made that consumers typically process ads in an extremely low-involved cursory manner. Moreover, psychology research suggests that gender differences in processing sexual stimuli are based on people's innate, gut-level affective responses that are more likely to emerge under reduced cognitive capacity," they say.

The authors invoke these lower-level responses in three experiments to see how they affect opinions about sex in ads.

They place participants under a high cognitive load, requiring them to memorise a large-digit number and recall it after they have viewed two ads. Since their cognitive capacities are tied up in remembering the number, it's expected they will give more spontaneous responses to the ads.

One ad shows an explicit sexual image of a naked couple, the other a landscape, and the results confirm the authors suspicion: the men in the group clearly prefer the sexual image whether it is relevant to the product or not (in one experiment the images advertise condoms, while in the other two it's watches).

Women generally view the sexual ad more negatively even when it is relevant and advertising condoms.

The authors say this gender difference was in line with a body of literature that shows differences in male and female attitudes to sex.

"Under the socialisation perspective, because of repeated and powerful conditioning, attitudes toward sex per se get automatically transferred to sexual stimuli, such as erotic pictures. Evolutionary views offer a similar prediction: because men are designed by natural selection to be favourably inclined to casual, non-invested sex, they will exhibit a positive affect response to portrayals of casual sex," they say.

However, the authors consider that attitudes to sex are more important than gender when it comes to sex in advertising and they show this to be the case.

The third experiment involves women only, who apart from their views of the ad and picture are also asked to respond to questions about their attitudes towards sex. Women with more liberal views are found to take a more positive view of an ad with a sexual image, even when it is irrelevant to the product, than women with conservative views.

Although the authors do not disagree with the earlier findings that both men and women deem gratuitous sex ads unethical and manipulative, they point out that the responses are different when they are targeted at gut-level reactions.

"Consumers who have favourable affective reactions toward sexual stimuli should evaluate sex-based ads positively in comparison to non-sexual ads, whereas the reverse should be observed for those with relatively unfavourable affective reactions," they say.

"From a practical perspective, this carries obvious implications for managers wishing to understand when and why the use of sex appeals might be effective across gender-defined segments."