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The sense of smell remains one of the least understood of our senses. We know the human nose has at least 400 odour receptors, allowing us to discriminate upwards of a trillion odours (Bushdid et al., 2014). Once detected, odours can trigger powerful positive or negative emotional responses and associated memories (Kadohisa, 2013). We detect odours in two ways: by sniffing our environment (orthonasal perception) and detecting odours released in our mouth during eating and drinking (retronasal perception). When we experience the “taste” of strawberries, for example, we are experiencing odour compounds released in our mouth alongside actual taste stimuli and other detected qualities such as texture, temperature etc. The multisensory integration of these diverse senses generates strawberries' overall “flavour” (Spence, 2015; Stevenson, 2010). Moreover, once we have co-experienced taste and retronasal odour together, we experience the associated taste-like qualities when we subsequently sniff these odours, a form of olfactory synaesthesia (Spence, 2016). This transfer of taste-like characteristics to odours through learning is the focus of this project, as this puzzling phenomenon offers a unique opportunity to study the fundamental nature of perception. At present, we only partially understand the changes to odour perception by association with tastes. We have little knowledge of how these changes are encoded in the brain. Our evaluation of odours also has two dimensions: perception and hedonics. Consequently, participants come to like odours paired with a liked taste and dislike odours they have co-experienced with a disliked taste (Stevenson & Boakes, 2004; Stevenson et al., 1995). Crucially, there are known individual differences in taste liking, particularly for sweet tastes. This means that although odours that have been paired with the sweet taste of sucrose subsequently are rated as smelling sweeter universally, that change in odour sweetness is accompanied by increased liking for the odour for sweet likers but the opposite hedonic response for sweet dislikers. This implies a clear neural separation of encoding of perception and hedonics. But the neural basis of this remains unknown and is the focus of this project. REFERENCES Bushdid, C., Magnasco, M. O., Vosshall, L. B., & Keller, A. (2014). Humans Can Discriminate More than 1 Trillion Olfactory Stimuli. Science, 343(6177), 1370-1372. https://doi.org/doi:10.1126/science.1249168 Kadohisa, M. (2013). Effects of odor on emotion, with implications [Mini Review]. Frontiers in Systems Neuroscience, 7. https://doi.org/10.3389/fnsys.2013.00066 Spence, C. (2015). Multisensory Flavor Perception. Cell, 161(1), 24-35. https://doi.org/10.1016/J.CELL.2015.03.007 Spence, C. (2016). Oral referral: On the mislocalization of odours to the mouth. Food Quality and Preference, 50, 117-128. https://doi.org/https://doi.org/10.1016/j.foodqual.2016.02.006 Stevenson, R. (2010). The Psychology of Flavour. https://doi.org/10.1093/acprof:oso/9780199539352.001.0001 Stevenson, R. J., & Boakes, R. A. (2004). Sweet and Sour Smells: Learned Synesthesia Between the Senses of Taste and Smell. In The handbook of multisensory processes. (pp. 69-83). Boston Review. https://doi.org/10.7551/mitpress/3422.001.0001 Stevenson, R. J., Prescott, J., & Boakes, R. A. (1995). The acquisition of taste properties by odors. Learning and Motivation, 26(4), 433-455. https://doi.org/10.1016/S0023-9690(05)80006-2

A project on subjective colour experience

Pre-registered analysis protocols for this project. The site will also host the behavioural data and provide information on how to acess the neuroimaging datasets when they become available.