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Smelling with Your Brain: How Our Sense of Smell Relies on Predictions and Visual Cues

Our brains are constantly trying to predict what will happen next, and this is especially true when it comes to our sense of smell, according to a new study published in the Journal of Neuroscience. Researchers from Stockholm University have found that our ability to identify odors is heavily influenced by cues from other senses, particularly vision.

The study, led by Stephen Pierzchajlo, a PhD student at the Department of Psychology, consisted of three experiments designed to compare how our senses of smell, sight, and hearing process expected and unexpected stimuli. Participants were given spoken word cues, such as “lemon,” and then presented with either a picture or a smell. They had to quickly decide whether the picture or smell matched the cue.

“The main finding is that smelling was much more dependent on predictions than vision was. This is interesting because many people think that smell is primitive and reactive, when our research shows it is in fact quite sophisticated and proactive,” said Pierzchajlo.

The researchers discovered that when participants were presented with unexpected smells, both the olfactory and visual areas of the brain were activated, even though no visual cues were present. This suggests that our sense of smell engages the visual brain to help identify unexpected odors.

“The olfactory brain thus has a completely unique way of processing smells and it is about whether the smells are expected or not. The sense of smell warns us of smells that we had not expected, and engages the visual brain, perhaps to be able to see what it is that smells. It’s a smart function because we humans are so bad at recognizing smells if we don’t get clues,” explained Jonas Olofsson, professor at the Department of Psychology and co-author of the study.

The study’s findings challenge the notion that our sense of smell is a primitive and reactive sense. Instead, it appears to be a proactive sense that relies heavily on predictions and cues from other senses to identify odors.

“We have all experienced that we react to when an unexpected smell appears, for example when we enter someone’s flat and encounter a new smell. Our research shows that the sense of smell is highly influenced by the cues from other senses, while the sense of sight and hearing are affected to a much lesser extent,” said Olofsson.

The experiments involved a total of 166 participants, with 69 completing the first behavioral experiment, 50 completing the second, and 32 participating in the fMRI portion of the study. The researchers used a set of four familiar stimuli (lavender, lilac, lemon, and pear) presented as smells, pictures, or spoken words to ensure high and comparable accuracy rates and unbiased response-time assessments.

Pierzchajlo, who is currently working on his PhD, sees this study as the first concluded part of his research. “The human sense of smell is not a reactive, but a proactive sense. It uses a unique brain strategy to process unexpected smells in order to understand what the smells are,” he said.

This groundbreaking research sheds new light on how our brains process sensory information and highlights the importance of cues from other senses in identifying odors. As we continue to learn more about the complex workings of our brains, studies like this one will help us better understand how we perceive and interact with the world around us.



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