The group solicited responses to a carefully graded spectrum of emotions starting with strong facial expressions classified as 100 per cent intensity and morphing by 10 per cent increments from extreme joy or sadness, for example, to neutral. Each participant was asked to say whether the face expressed happiness, sadness, anger, disgust or fear.
“We arrived at the lowest intensity of expression needed for a person to start judging correctly the emotion it represented. We knew 100 per cent was unnecessary, but we wanted to know what the minimum would be. We found that it was mostly between 20 per cent and 30 per cent of the total content of the emotion concerned,” Gualtieri explained.
Having determined the intensity threshold required for participants to perceive these emotions, they then measured the time taken to reach a conclusion (response time). Lastly, they observed how this could be modified by the presence of pleasant and unpleasant smells.
“We showed how this effect results from all sensory modes. All five senses must interact so that human beings can adapt to their surroundings, communicate and survive. The article describes an example of this,” Gualtieri said. “The presence of a smell, whether or not I’m aware of it, will affect my visual processing and how I interpret visual stimuli as emotions.”
Individual judgments
Another novel aspect of the experiment was that each participant was allowed to decide whether smells were good or bad, rather than being required to use pre-defined categories. “Many studies of this kind use a methodology based on categories so that participants necessarily classify the smell of strawberries as pleasant and foot odour as bad. There are these ready-made labels. But we know from experience that it’s complicated, especially as far as smells are concerned, and the categories don’t always fit,” Gualtieri said.
He added, “Our analysis was based on the judgments of individual participants, on whether they found a smell pleasant or unpleasant. That was a major difference in the methodology we used, compared with the typical approach based on labels that assume a particular smell is always good or bad. This choice influenced our results significantly. We decided to conduct the entire procedure on the basis of the participants’ individual judgments of pleasantness or unpleasantness.”
The study sample comprised 20 women and 15 men. The participants did not know it was about the smell. They were told only that its purpose was to measure the speed at which they detected the emotions conveyed by facial expressions. “We didn’t say anything about smells. A very small amount of a certain substance [butyric acid, smelling of rancid butter; isoamyl acetate, with a strong banana-like odour; or lemongrass scent] was placed in the foam of the headset microphone they used as they were sitting in front of the screen. The participants themselves conducted the entire experimental session to identify emotions, and we measured the success rates and response times,” Gualtieri said.
After this part was completed, the researchers explained that the purpose of the study was to find out whether the judgment of the emotions conveyed by facial expressions was affected by smells. The participants then rated each smell for pleasantness using a dial with a scale.
Patricia Renovato Tobo, Scientific Manager at Natura Inovacao e Tecnologia de Produtos, a subsidiary of Natura Cosmeticos, and Carla Regina Barrichello, also affiliated with Natura, are the other co-authors of the article.
“The extent to which the hedonic valence of smells influences the emotional processing of visual stimuli had been highlighted in previous studies, but we knew several other factors could be involved. Our study showed the significant interaction between olfactory and visual stimuli, so that smells influence the identification of facial expressions and facial expressions influence the emotional response to smells,” Tobo said.