The sense of smell is affected more by cues from other senses than the sense of sight and hearing, according to a new study published in the Journal of Neuroscience. This supports the theory that the brain’s main function is to predict what will happen next, reacting mainly to unexpected events. Previous research on this topic, known as predictive coding, has mainly focused on the ways in which the brain reacts to unexpected events.We observe, yet it remains unknown if our various senses, including smell, operate in similar ways. To delve deeper into the connection between smell and the processing of diverse sensory stimuli, a group of researchers conducted a study consisting of three experiments. This included two behavioral experiments and one experiment utilizing the brain imaging method fMRI at Stockholm University Brain Imaging Centre (SUBIC).
“The key discovery is that the sense of smell relies much more on predictions compared to vision. This finding is intriguing because many assume that smell is instinctual and reactive, whereas our research indicates that it is actually quite advanced and proactive,” explained Stephen.Pierzchajlo, a PhD student at the Department of Psychology, is the main author of the study. The study demonstrates the importance of accurate sensory cues in classifying different sensory impressions. “We have all experienced reacting to an unexpected smell, such as when we encounter a new smell in someone’s flat. Our research shows that the sense of smell is greatly influenced by cues from other senses, while the sense of sight and hearing are affected to a much lesser extent,” explains Jonas Olofsson, professor at the Department of Psychology and co-author of the study.
Researchers found that when the brain encounters unexpected odors, both the olfactory and visual areas of the brain become active, even when there are no visual cues present in the task.
This unique processing of smells by the olfactory brain is based on whether the smells are expected or not. The sense of smell alerts us to unexpected odors and activates the visual brain, possibly to help us identify the source of the smell. This function is intelligent because humans struggle to recognize smells without hints,” said Jonas Olofsson.
In the
In the experiments, participants were asked to listen to spoken word cues like “lemon,” and then they were given a picture or a smell. The participants had to quickly decide whether the picture or smell matched the cue, such as with a lemon picture or smell, or did not match, such as with a rose picture or smell.
“We found that in general, the expected pictures and smells resulted in faster decisions, which supports the predictive coding theory. We used the difference in response time to compare the senses with each other – a longer delay for unexpected stimuli indicates that the sense relies more on predictions,” explained Stephen Pierzchajlo.
This study is the first of its kind.Included in his PhD research was a statement from Stephen Pierzchajlo about the human sense of smell, emphasizing its proactive nature and unique brain strategy for processing unexpected smells. The study conducted three experiments, two behavioral and one using the fMRI brain imaging method at Stockholm University Brain Imaging Centre (SUBIC). A total of sixty-nine participants completed the first behavioral experiment, and fifty completed the second.The researchers initially gathered and analyzed data from 15 participants before involving 32 healthy volunteers in the fMRI part of the study. For all three experiments, the researchers used four familiar stimuli (lavender, lilac, lemon, and pear) presented as smells, pictures, or spoken words to ensure accurate and unbiased response-time assessments.
