title: The Multisensory Mouth: An investigation into the motivational, affective, and cognitive mechanisms, driving oral behaviours
Creators: name: Hagan, R
Publisher: name: Liverpool John Moores University
Year: 2025

description: Consumer goods and healthcare companies face significant challenges in effectively marketing their products, particularly in sectors such as food and oral health, where sensory experiences such as taste and smell play a central role in shaping consumer perceptions and purchasing decisions (Purcarea, 2019). One important aspect of product success is understanding how sensory cues influence not only immediate product liking but also long-term preferences and consummatory behaviours (Sagha et al., 2022). However, sensory experiences are not standardised across consumer populations. While cultural factors influence acceptance of certain textures or aromas (Jeong &amp; Lee, 2021), individual differences in taste sensitivity and odour perception, for example, also significantly shape consumer responses to products (Carlson et al., 2018; Cliff &amp; Green, 1996), suggesting a more segmented approach to product development and marketing can be beneficial (Manrique &amp; Zald, 2006). Difficulties arise, however, in establishing research methodologies which effectively capture individual variations in product perception and enjoyment (Spence, 2015). Traditional consumer methods, such as, focus groups and questionnaires, have limitations not only in their susceptibility to cognitive biases and demand characteristics, that lead to socially desirable or consciously filtered responses, but also in the fact they disrupt natural, on-going behaviours. For example, asking someone to consciously reflect on how much they 'like' something while still consuming it can influence their natural responses (Boesveldt &amp; de Graaf, 2017). Moreover, these methods fail to capture spontaneous and automatic emotional responses to sensory stimuli, which can occur outside conscious perception and are central to understanding authentic consumer behaviour (Mastinu et al., 2022; Kaneko et al. 2018). 
To address these limitations, objective, real-time assessment techniques are needed, which capture unconscious emotional and physiological responses to a product’s sensory cues. For example, in the oral health sector, understanding how variations in taste sensitivity influence responses to menthol can help in the development of more appealing, segment targeted products. Similarly, physiological insights into how sensory cues influence food choices can guide the development of healthier food products while also helping to identify which sensory attributes resonate most strongly with different consumer segments (McCrickerd &amp; Forde, 2016). Therefore, the studies within this PhD use behavioural and physiological methods to increase understanding of 1) how sensory and perceptual differences influence product perception and liking and 2) which real-time measures of consumer experience are the best predictors of product enjoyment. Motivating individuals to purchase or consume certain foods is driven by a complex interplay of psychological and sensory factors. Understanding what drives this motivation is essential for both food manufacturers and marketers, who seek to align their products with consumer desires. However, measuring these motivations presents a significant challenge, as motivation itself is an internal psychological construct that cannot be directly observed. Whilst assessments of the motivational value of food rewards have largely relied on subjective rating scales (Chae et al., 2023; Morquecho-Campos, 2021; Proserpio et al., 2019; Ramaekers et al., 2014; Gaillet et al., 2013; Rolls &amp; Rolls, 1997), these often fail to capture implicit processes and are susceptible to biases (Chong et al., 2016). Behavioural measures, such as food selection, provide more objective insights but are susceptible to demand characteristics, which can subtly influence participants’ decisions and obscure genuine motivational effects. To address these limitations, effort-based measures, which quantify motivation by the effort exerted to obtain a reward, offer an objective alternative (Mela, 2006; Pool et al., 2016). Research in both animals and humans has demonstrated that measures like progressive ratio schedules (Zepeda-Ruiz et al., 2020; Velazquez-Sanchez et al., 2015), key pressing (Temple, 2016; Rogers &amp; Hardman, 2015), and grip-force dynamometers (Ziauddeen et al., 2014) can effectively capture changes in motivational state associated with sensory-specific satiety. Specifically, effort decreases for previously consumed foods, while remaining unchanged for novel ones. One of the central questions addressed in this thesis is whether exposure to ambient food odours produces a motivational priming or satiety effect, and how these effects can be objectively measured. Theories of incentive motivation, (e.g. Berridge &amp; Robinson 1998), distinguish between the mechanisms of 'wanting', a motivational drive to obtain a reward, and liking, the sensory pleasure derived from consumption of a food reward. While 'wanting' is often a non-conscious process driven by external cues, 'liking' represents a conscious hedonic experience felt during and immediately following consumption. Here, employing an effort-based measure of incentive motivation, specifically, a grip-force paradigm, (Study 1, Chapter 3) provides an objective assessment of how olfactory cues influence 'wanting' for congruent foods. The grip-force paradigm allows for the measurement of physical effort exerted to obtain a reward, providing a direct measure of motivation that is less vulnerable to cognitive biases than traditional self-report and food selection methods. This approach builds on earlier studies that have demonstrated the validity of effort-based tasks in assessing incentive motivation for food (Pessiglione et al., 2007; Ziauddeen et al., 2012), a finding which is replicated in study 2 (Chapter 4). These findings have important implications for food marketing and oral health strategies. For instance, the impact of odour cues, may depend not only on factors such as timing, intensity, or odour type, but also on the methods used to measure consumer responses. A deeper understanding of how to accurately measure consumer motivation for products, could ultimately help companies design more effective product designs and marketing strategies, increasing product selection and consumption. Beyond understanding how to measure and manipulate consumer motivation for products, it is also important to understand the individual variations in how people perceive products. In the food and personal care industry, aroma and fragrance are important predictors of consumer liking, and drivers of purchase (Milotic, 2003). Existing research suggests humans find it challenging to identify individual odours within even simple mixtures, with performance declining rapidly as the number of components increases beyond three (Le Berre et al, 2007; Laing &amp; Francis 1989) even with extensive training and experience (Livermore &amp; Laing 1996). Possibly due to perceptual phenomena such as odour blending (Le Berre et al, 2010), masking (Stevenson et al, 2007), and synergy (Thomas-Danguin et al, 2014). For instance, in odour blending, different smells fuse to form a unique composite scent, whilst in odour masking, stronger smells suppress weaker ones. However, while research on olfactory mixture perception has provided valuable insights into odour processing, the traditional approach of relying on single volatile mono-molecule odourants (Castro et al, 2021) such as vanillin (Chen et al., 2013) for understanding olfactory processing, may present limitations. This is because, odours encountered in natural settings are typically complex, multi-molecular mixtures that combine to form a unified percept (Thomas-Danguin et al, 2014), such as, roasted coffee (Grosch et al, 2000). As such, standard methods may not fully capture the complexity of natural odour experiences, potentially limiting the ecological validity and applicability of the findings to real-world olfactory perception. Comparable to the visual domain, where scene-analysis is processed through both local (analytical) and global (configural) perspectives, olfaction also relies on a balance between local and global processing to make sense of complex odour environments (Rokni et al, 2014). Whilst global processing enables us to perceive odour mixtures as unified, cohesive odour objects, capturing the overall character of a smell, local processing allows for the identification of individual components within a mixture (Thomas-Danguin, 2014), such as detecting the subtle hint of vanilla in a cup of coffee or the various fruity, earthy, or floral notes in wine. However, studies of perceptual scene analysis have predominantly focused on single sensory modalities, without exploring domain-general processing across senses. Evidence from other sensory domains suggests that individual differences in processing styles, such as biases for local versus global processing, can be influenced by both state and trait factors. For example, changes in affective state can influence processing style, with negative affect associated with enhanced local processing and positive affect with enhanced global processing (Gasper &amp; Clore, 2002; de Groot et al., 2015). Additionally, a stable bias for local processing has been observed in autistic individuals and those with higher levels of autistic traits (Neufeld et al., 2019; Happé &amp; Booth, 2008). As such, a further aim of this thesis (Study 3, Chapter 5) is to increase understanding of the cognitive processes underlying olfactory scene analysis by determining whether ability to identify odour objects against a complex background is predicted by a visual perceptual style. Understanding how these processing styles operate in olfaction, could provide valuable insights for consumer goods companies, supporting the design of targeted marketing strategies or the creation of product variations that appeal to specific consumer segments. Building on these individual differences in sensory processing, it is also important to consider how genetic differences in oral perception contribute to food preferences and consumption behaviours, which have important implications for food marketing in real-world settings. One example is the variation in sensitivity to the bitter compound 6-n-propylthiouracil (PROP), which categorises individuals as super-tasters, medium-tasters, or non-tasters based on their sensitivity to the bitter tasting compound, 6-n-propylthiouracil (PROP) (Bartoshuk et al., 2003; Bartoshuk et al., 1998; Delwiche et al., 2001). Super-tasters, who have a heightened sensitivity to bitterness, often exhibit stronger aversions to bitter foods, which can influence their overall dietary choices (Bartoshuk, 1991). These genetic differences not only affect the perception of bitter tastes but are also believed to extend to other oral sensations, such as astringency (Pickering &amp; Robert, 2006) and chemesthetic properties (Bartoshuk et al, 1993; Prescott &amp; Swain-Campbell, 2000; Prescott et al, 2004). As a result, individuals with varying taster statuses experience these oral sensations in markedly different ways, leading to a wide range of subjective food experiences. While some research has reported no associations between taster status and food preference (Dinehart et al., 2006; Yackinous &amp; Guinard, 2006; Jerzsa-Latta et al., 1990), indicating that personality traits, culture, and experience can also impact food choices (Tepper et al., 2009), several studies have highlighted the health-related implications of taster status, particularly in relation to body-mass index (BMI). For example, non-tasters have been found to have higher BMI compared to their super-taster counterparts. Such differences in taste sensitivity and their resulting preferences underscore the need for tailored approaches in understanding taste preferences and consumption behaviours. To date, a vast majority of consumer research on product liking has relied on subjective measures, such as self-report ratings and questionnaires (Lim, 2011; Cordonnier &amp; Delwiche, 2008; Meiselman &amp; Cardella, 2003). However implicit psychophysiological techniques, such as facial electromyography (EMG), offer a powerful and objective approach for understanding hedonic responses to oral stimuli during consumption. Facial EMG measures subtle muscle activities that occur in response to emotional stimuli, including the facial expressions associated with positive or negative reactions to food. By capturing involuntary facial reactions, such as the activity of the corrugator supercilii (associated with brow lowering) and zygomatic major muscles (associated with smiling or lip corner pulling), facial EMG allows for a more nuanced and accurate understanding of consumer response than subjective ratings can provide (Cacioppo et al., 1992; Dimberg et al., 1990). Specifically, increased activity in the corrugator supercilii has been found to be negatively correlated with perceived pleasantness, while activity in the zygomatic major muscle is positively correlated with positive emotional responses, such as enjoyment (Sato et al., 2020a). An advantage of facial EMG is that it continuously monitors these subtle facial muscle movements without requiring participants to consciously reflect on or interrupt their on-going behaviour, allowing researchers to capture real-time, spontaneous emotional reactions that are unconscious and automatic (Bell et al., 2018; Hebert et al., 2008). Therefore, a final aim of this thesis (study 4, chapter 6) is to investigate whether PROP Taster Status is predictive of subjective liking of threshold and suprathreshold concentrations of bitter, astringent and chemesthetic compounds, and determine whether facial EMG, can predict individual differences in dis/liking of these stimuli. The importance of this programme of research lies in its potential to bridge the gap between laboratory-based studies of sensory perception and real-world consumer behaviour. Traditional sensory testing methods, such as self-report questionnaires or basic taste tests, often fail to capture the complexity of consumer responses, relying heavily on conscious introspection and subjective assessments that can be influenced by biases or demand characteristics (Bell et al. 2018; Hebert et al. 2008). By employing objective measures of motivation and affective response, this thesis aims to increase understanding of how sensory cues influence food-related behaviours. This approach builds on and expands typical consumer and sensory testing by incorporating physiological measures, such as facial EMG, that offer real-time insights into unconscious emotional reactions. For the oral-care and food industries, insights into how sensory cues such as taste and smell shape consumer preferences can inform product development and marketing strategies, leading to more effective targeting of various consumer populations and the development of products that resonate with specific sensory profiles.