The role of top-down processing in olfactory habituation

This thesis delves into the intriguing concept of habituation within the olfactory domain, which refers to the decreased response to odours over time. The process of adaptation leads to habituation, but the extent to which peripheral and central regions contribute to this mechanism remains uncertain. The thesis aims to investigate the contribution of central processes and cognitive effects to olfactory habituation, with the goal of mitigating receptor fatigue. To achieve this goal, a comprehensive series of studies were conducted. These studies involve controlled exposure to a range of odours, with concurrent monitoring of participants' responses throughout the exposure period. Chapter 5 of the thesis outlines a study focused on preventing olfactory peripheral adaptation by using imagined odours as a proxy for actual odours. Imagined odours do not stimulate olfactory receptors, so it was found that habituation to them may reflect the role of cognitive processes. Potential challenges associated with the adoption of imagined odours are thoroughly discussed. Moving on to Chapter 6, the study examines cognitive influences on olfactory habituation, specifically the impact of knowledge about edibility. These studies examine whether the edibility of an odour can influence the perceived intensity and pleasantness of the odour over time. These research employs intermittent presentation of stimuli and a 30-second interval between odour presentations to minimise receptor adaptation and emphasise central olfactory processes. The main findings of these research revealed that food stimuli are more resistant to olfactory habituation compared to nonfood ones. Finally, the study reported in Chapter 7 investigates how repeated presentations of the same food odour affect visual attention and preferences for congruent food products. The attentional bias towards food odours remained consistent over time, suggesting that food odours maintain their salience and continue to direct visual attention towards congruent visual products over time. However, despite the absence of olfactory habituation, repeated odour presentations lead to a reduction in preference for congruent products. In summary, this thesis ventures into the captivating realm of olfactory habituation, unravelling its multifaceted nature and shedding light on its intricate mechanisms. Investigation of the interplay between sensory adaptation, cognitive processes, and their cumulative impact on olfactory experiences has yielded valuable insights. As we journeyed through the chapters, we explored strategies such as employing imagined odors to minimize peripheral adaptation, revealing the cognitive underpinnings of habituation. We also discerned the nuanced effects of knowledge on edibility and the resilient nature of food-related stimuli. Additionally, our investigation into the interconnection of olfaction and visual attention revealed a persistent attentional bias. Yet, while habituation did not occur, preferences for congruent food products evolved. As we conclude this exploration, we are equipped with a deeper understanding of olfactory habituation's complexities, paving the way for innovative strategies to counter receptor fatigue and enrich olfactory encounters.