Men are more likely to think of women as objects if they have looked at sexy pictures of females beforehand, psychologists said yesterday.

Researchers used brain scans to show that when straight men looked at pictures of women in bikinis, areas of the brain that normally light up in anticipation of using tools, like spanners and screwdrivers, were activated.

Scans of some of the men found that a part of the brain associated with empathy for other people's emotions and wishes shut down after looking at the pictures.

Susan Fiske, a psychologist at Princeton University in New Jersey, said the changes in brain activity suggest sexy images can shift the way men perceive women, turning them from people to interact with, to objects to act upon.

The finding confirms a long-suspected effect of sexy images on the way women are perceived, and one which persists in workplaces and the wider world today, Fiske said.

"When there are sexualised images in the workplace, it's hard for people not to think about their female colleagues in those terms. It spills over from the images to the workplace," she said.

Speaking at the American Association for the Advancement of Science meeting in Chicago yesterday, Fiske said the findings called into question the impact of sexualised images of women that might be pinned on workplace walls or sent around offices where there was a strong locker-room culture.

"I'm not saying there should be censorship, but people need to be aware of the associations people will have in their minds," Fiske said.

In the study, Fiske's team put straight men into an MRI brain scanner and showed them images of either clothed men and women, or more scantily clad men and women. When they took a memory test afterwards, the men best remembered images of bikini-clad women whose heads had been digitally removed.

The brain scans showed that when men saw the images of the women's bodies, activity increased in part of the brain called the premotor cortex, which is involved in urges to take action. The same area lights up before using power tools to do DIY. "It's as if they immediately thought to act on theses bodies," Fiske said.

In the final part of the study, Fiske asked the men to fill in a questionnaire that was used to assess how sexist they were. The brain scans showed that men who scored highest had very little activity in the prefrontal cortex and other brain regions that are involved with understanding another person's feelings and intentions. "They're reacting to these women as if they're not fully human," Fiske said.