What you smell is influenced by your other senses, study finds
Our sense of smell interacts with other senses, revealing surprising insights into how our brains process sensory information.
Our sense of smell interacts with other senses, revealing surprising insights into how our brains process sensory information. (CREDIT: Creative Commons)
A recent study published in the Journal of Neuroscience sheds light on how our sense of smell interacts with other senses, revealing surprising insights into how our brains process sensory information.
The study, conducted by researcher's at the Stockholm University Brain Imaging Centre (SUBIC), suggests that smell is not as primitive and reactive as previously thought but rather operates in a sophisticated and proactive manner.
The research, led by Stephen Pierzchajlo, a PhD student at the Department of Psychology, focused on a concept known as predictive coding, which posits that the brain's primary function is to predict future events based on incoming sensory input.
While previous studies have primarily explored predictive coding in the context of vision, this study aimed to investigate whether similar principles apply to other senses, particularly smell.
To explore this further, the researchers conducted a series of experiments, including two behavioral experiments and one using functional magnetic resonance imaging (fMRI) at the Stockholm University Brain Imaging Centre (SUBIC). The results revealed that smell is significantly more reliant on predictive cues compared to vision.
Pierzchajlo explains, "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."
One of the co-authors of the study, Professor Jonas Olofsson, highlights the importance of understanding how different senses interact, stating, "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."
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The study also revealed that unexpected odors activate both the olfactory and visual regions of the brain, suggesting a unique processing mechanism for smells.
Olofsson elaborates, "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."
Experiments into smell and its connection to other senses
In the experiments, participants were presented with spoken word cues, such as "lemon," followed by either a picture or a smell. They were then required to quickly determine whether the stimulus matched the cue or not. The results showed that expected stimuli led to quicker decisions, supporting the predictive coding theory.
Pierzchajlo emphasizes, "Overall, the expected pictures and smells led to quicker decisions, which fits well with predictive coding theory. We used the difference in response speed to compare the senses with each other – a bigger delay for unexpected stimuli means that the sense relies more on predictions."
This study represents the first part of Pierzchajlo's PhD research, offering valuable insights into the proactive nature of the human sense of smell. He concludes, "The human sense of smell is not reactive but proactive. It uses a unique brain strategy to process unexpected smells in order to understand what the smells are."
Study Methodology
Three experiments were conducted in the study, two behavioral experiments and one fMRI-experiment using the brain imaging method fMRI at Stockholm University Brain Imaging Centre (SUBIC).
Sixty-nine participants completed the first behavioral experiment. Fifty participants completed the second behavioral study.
For the fMRI-experiment, data for 15 participants were first collected and analyzed. Then, 32 healthy volunteers participated in the fMRI portion of the study.
In all three experiments, the researchers used a set of four familiar stimuli (lavender, lilac, lemon and pear) that were repeatedly presented as smells, pictures or spoken words, in order to achieve high and comparable accuracy rates and thus unbiased response-time assessments.
By unraveling the mysteries of smell processing, scientists are gaining a deeper understanding of the complexities of human perception.
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