The smell of citrus promotes generosity, while dim rooms increase dishonesty and selfish behaviour, psychology researchers suggest in recent studies.

Chen-Bo Zhong, a psychologist at the University of Toronto, and his colleagues in the U.S. have conducted a series of small experiments designed to test how changes in an environment — differences in lighting or smell — can affect human behaviour.

In one experiment, participants were given $10 in change and 20 mathematical problems, and sent into either a room brightly lit with florescent lights or one with a third as many lights on.

The subjects were asked to complete as many of the problems as they could in five minutes and to keep 50 cents for each problem they solved. They were asked to put the rest of the change in an envelope when they were done.

Typically, the participants were able to complete seven problems in the time allowed, but since the test was anonymous, they could keep as much of the money as they wanted without getting caught.

While the tests had no names or numbers on them, the problems themselves revealed whether the participant had been in a brightly lit room or a dim one.

Dark offers anonymity

"What we found was that participants randomly assigned to the dimmer room … were more likely to lie or cheat compared with participants in the well-lit room," Zhong said.

Zhong said that the rooms with the dim lighting created a sense of anonymity, what he calls illusory anonymity.

"The idea is that when we experience darkness, we disregard what other people may still be able to see or hear or observe," he said. "The illusory sense of anonymity can license unethical behaviour."

In interviews with the participants after the experiments about what happened and what determined their behaviour, few of the participants even noticed the difference in lighting.

In a similar study, participants were asked to wear either a pair of sunglasses or a pair of glasses with clear lenses.

"What we found was that wearing a pair of sunglasses led to greater self-interested behaviour," said Zhong.

Zhong said the sunglasses didn't make the participants anonymous or less visible, of course, but still had an effect on their behaviour, making them less likely to see themselves from another person's perspective.

"We perceive ourselves to be anonymous even if the darkness only applies to ourselves, as in the case where we wear a pair of sunglasses or are in a room that is dim but not exactly dark," Zhong said.

Zhong likened the sunglasses experiment to toddlers playing peek-a-boo.

"This is almost like kids playing a hide-and-seek game who will close their eyes and think that other people won't be able to see them," he said.

Scents affect ethics

The subconscious changes in behaviour weren't limited to visual changes. Zhong conducted similar experiments that used the sense of smell.

Participants were randomly assigned to rooms, some sprayed with citrus-scented window cleaner. In some of the experiments, the participants played a game of trust with an anonymous partner, again involving money.

The way the game typically works is that one partner is given a sum of money and told to put some or all of the money in an envelope. He is told his anonymous partner will receive triple that amount and will give some of the money back. Of course, the second partner could just keep all the money.

In Zhong's experiment, the participants played the role of the second partner and were all told their partner had given them the full mount, $4, which was then tripled to $12.

The participants were free to anonymously return some or none of the money.

"What we found was that in the citrus-scented room, people were more likely to engage in good behaviours," Zhong said. "They were more likely to honour the trust that other people displayed."

Real-world questions

Zhong said that it would be interesting to see how the findings would translate to real-world situations.

"Based on the experiments we have conducted and the findings we've found, I think it's reasonable to speculate that people in a real environment, where they can smell these scents that are associated with purity and cleanliness, also may tend to be behave more ethically or socially," he said.

In another paper published prior to Zhong's, researchers found people eating cookies in a citrus scented room were less likely to leave crumbs behind than those in an unscented room.

Zhong said he wanted to take that finding to the next level, to explore the "metaphorical and psychological connections between physical cleanliness and moral purity."

English is full of metaphors relating cleanliness to moral behaviour, from "clean conscience" to "money laundering" to "dirty jokes."

In previous research, Zhong and his colleagues explored the connection between unethical behaviour and physical cleanliness, something Zhong called the Lady Macbeth effect, after the Shakespeare character who obsessively washed her hands because of her role in the murder of the king ("Out, damn spot. Out, I say!").

"We asked people to recall unethical behaviours they have done, like lying to parents or betraying their friends," Zhong said. Another group was asked about their prior ethical acts.

The participants were then asked to rate items on a list of products by how much they wanted them. The participants who were asked about their unethical behaviour were more likely than the other group to rate cleaning products higher than household products that have nothing to do with cleaning, such as CDs.

Zhong said these findings suggest that abstract concepts, such as morality, or even time, are connected to physical experience. We think "back" to the past and look "forward" to the future, for example.

"Human perception or cognition are not as abstract as we typically assume," Zhong said. "We don't simply store information in our brain. Instead, our cognition is much richer than that. For every abstract construct we associate physiological experience."

The metaphorical connections could even transcend language barriers, although Zhong said there hasn't been research to see if the behaviour is consistent across cultures.

"In Chinese, we refer to a pair of dirty hands, for example, to refer to someone who steals."