Experience dependent changes in odour-viscosity perception

The role of viscosity in flavor preference: plasticity and interactions with taste

The brain combines gustatory, olfactory, and somatosensory information to create our perception of flavor. Within the somatosensory modality, texture attributes such as viscosity appear to play an important role in flavor preference. However, research into the role of texture in flavor perception is relatively sparse, and the contribution of texture cues to hedonic evaluation of flavor remains largely unknown. Here, we used a rat model to investigate whether viscosity preferences can be manipulated through association with nutrient value, and how viscosity interacts with taste to inform preferences for taste + viscosity mixtures. To address these questions, we measured preferences for moderately viscous solutions prepared with xanthan gum using 2-bottle consumption tests. By experimentally exposing animals to viscous solutions with and without nutrient value, we demonstrate that viscosity preferences are susceptible to appetitive conditioning. By independently varying viscosity and taste content of solutions, we further show that taste and viscosity cues both contribute to preferences for taste + viscosity mixtures. How these 2 modalities are combined depended on relative palatability, with mixture preferences falling in between component preferences, suggesting that hedonic aspects of taste and texture inputs are centrally integrated. Together, these findings provide new insight into how texture aspects of flavor inform hedonic perception and impact food choice behavior.

Bioactive Carbohydrate Polymers-Between Myth and Reality

Polysaccharides are complex macromolecules long regarded as energetic storage resources or as components of plant and fungal cell walls. They have also been described as plant mucilages or microbial exopolysaccharides. The development of glycosciences has led to a partial and difficult deciphering of their other biological functions in living organisms. The objectives of glycobiochemistry and glycobiology are currently to correlate some structural features of polysaccharides with some biological responses in the producing organisms or in another one. In this context, the literature focusing on bioactive polysaccharides has increased exponentially during the last two decades, being sometimes very optimistic for some new applications of bioactive polysaccharides, notably in the medical field. Therefore, this review aims to examine bioactive polysaccharide, taking a critical look of the different biological activities reported by authors and the reality of the market. It focuses also on the chemical, biochemical, enzymatic, and physical modifications of these biopolymers to optimize their potential as bioactive agents.

In-mouth attributes driving perceived quality of Pinot noir wines: Sensory and chemical characterisation

We investigated perception of mouthfeel in Pinot noir wines and its physicochemical determinants. Seventeen wine professionals judged 18 Pinot noir wines via two tasting tasks, Descriptive Rating and Directed Sorting, the latter based on perception of in-mouth attributes. Selected chemical measures of the same 18 wines were determined. Sensory results demonstrated that mouthfeel attributes driving high quality were smoothness/silky/velvety, volume/fullness/roundness, overall body, and viscosity/mouth-coating, while the taste of bitterness and perceived tannin harshness drove low quality judgments. Perceived astringency and expressions of tannin (e.g., soft; harsh; fine) drove sorting behaviour of participants. Partial least squares regression (PLSR) was used to associate perceived in-mouth phenomena and chemical composition. The phenolic profile, in particular tannin concentration and structure, was the most important predictor of astringency and its sub-components. These results have important implications for wine producers aiming to enhance perceived quality in their Pinot noir wines.

Crossmodal Interactions Between Olfaction and Touch Affecting Well-Being and Perception of Cosmetic Creams

In the present series of studies, we investigated crossmodal perception of odor and texture. In four studies, participants tried two textures of face creams, one high viscosity (HV) and one low viscosity (LV), each with one of three levels of added odor (standard level, half of standard, or base [no added odor]), and then reported their levels of well-being. They also reported their perceptions of the face creams, including liking (global liking of the product, liking of its texture) and “objective” evaluations on just about right (JAR) scales (texture and visual appearance evaluations). In Study 1, women in France tried the creams on their hands, as they would when testing them in a store, and in Study 2, a second group of French women tried the creams on their faces, as they would at home. In Studies 3 and 4, these same two procedures were repeated in China. Results showed that both odor and texture had effects on well-being, liking, and JAR ratings, including interaction effects. Though effects varied by country and context (hand or face), the addition of odor to the creams generally increased reports of well-being, global liking and texture liking, in some cases affecting the “objective” evaluations of texture. This is one of the first investigations of crossmodal olfactory and tactile perception's impacts on well-being, and it reinforces previous literature showing the importance of olfaction on well-being.

Odor-Taste Interactions in Food Perception: Exposure Protocol Shows No Effects of Associative Learning

Repeated exposure can change the perceptual and hedonic features of flavor. Associative learning during which a flavor's odor component is affected by co-exposure with taste is thought to be central in this process. However, changes can also arise due to exposure to the odor in itself. The aim of this study was to dissociate effects of associative learning from effects of exposure without taste by repeatedly presenting one odor together with sucrose and a second odor alone. Sixty individuals attended two testing sessions separated by a 5-day Exposure Phase during which the stimuli were presented as flavorants in chewing gums that were chewed three times daily. Ratings of odor sweetness, odor pleasantness, odor intensity enhancement by taste, and odor referral to the mouth were collected at both sessions. Consistent with the notion that food preferences are modulated by exposure, odor pleasantness increased between the sessions independently of whether the odor (basil or orange flower) had been presented with or without sucrose. However, we found no evidence of associative learning in any of the tasks. In addition, exploratory equivalence tests suggested that these effects were either absent or insignificant in magnitude. Taken together, our results suggest that the hypothesized effects of associative learning are either smaller than previously thought or highly dependent on the experimental setting. Future studies are needed to evaluate the relative support for these explanations and, if experimental conditions can be identified that reliably produce such effects, to identify factors that regulate the formation of new odor-taste associations.

Effect of aroma perception on taste and mouthfeel dimensions of red wines: Correlation of sensory and chemical measurements

The present study was aimed at increasing the understanding of red wine mouthfeel by investigating the potential cross-modal effect of aroma and establishing relationships between sensory dimensions and chemical measurements. Investigations involved a set of 42 non-wooded red wines that were described with a novel application of a variant of the rate-all-that-apply sensory methodology ("rate-K attributes") by a group of Spanish wine experts under two conditions: (1) with no aroma perception (using nose clips) and (2) with aroma perception. In parallel, ethanol content, pH, titratable acidity, tannin activity, concentration of tannins, and spectroscopic measures of wines were determined. Results suggest that aroma does not play a main effect on taste or mouthfeel perception of red wines, except for oily mouthfeel, which was hypothesised to be masked by earthy aromas and enhanced by alcoholic nuances attributed to cognitive interactions. Independent and non-correlated mouthfeel dimensions such as dry/silky and sticky, grainy, prickly or oily were also identified. Tannin activity was shown to be highly positively correlated to dry on the palate, and tannin concentration with both overall dry and dry on the palate. A significant partial least squares regression model showed that tannin concentration and activity (positive contribution) as well as pH values (negative) were good predictors of the mouthfeel dimension mainly related to dry and sticky terms.

Odor Identification in Rats: Behavioral and Electrophysiological Evidence of Learned Olfactory-Auditory Associations

The ability to recognize and identify a smell is highly dependent on multisensory context and expectation, for example, hearing the name of the odor source. Here, we develop a novel auditory-odor association task in rats, wherein the animal learns that a specific auditory tone, when associated with a specific odor, predicts reward (Go signal), whereas the same tone associated with a different odor, or vice versa, is not (No-Go signal). The tone occurs prior to the onset of the odor, allowing physiological analyses of sensory-evoked local field potential (LFP) activity to each stimulus in primary auditory cortex and anterior piriform cortex (aPCX). In trained animals that have acquired the task, both auditory and subsequent olfactory cues activate β band oscillations in both the auditory cortex and PCX, suggesting multisensory integration. Naive animals show no such multisensory responses, suggesting the response is learned. In addition to the learned multisensory evoked responses, functional connectivity between auditory cortex and PCX, as assessed with spectral coherence and phase lag index (PLI), is enhanced. Importantly, both the multi-sensory evoked responses and the functional connectivity are context-dependent. In trained animals, the same auditory stimuli presented in the home cage evoke no responses in auditory cortex or PCX, and functional connectivity between the sensory cortices is reduced. Together, the results demonstrate how learning and context shape the expression of multisensory cortical processing. Given that odor identification impairment is associated with preclinical dementia in humans, the mechanisms suggested here may help develop experimental models to assess effects of neuropathology on behavior.

Perceptual and cognitive determinants of tactile disgust

Tactile cues are said to be potent elicitors of disgust and reliable markers of disease. Despite this, no previous study had explored what the full range of tactile properties are that cue disgust, nor how interpretation of these sensations influences disgust. To answer these questions, participants were asked to touch nine objects, selected to cover the range of tactile properties, and evaluate their sensory, affective, and risk-based characteristics (primarily how sick they thought the object would make them). Object contact was manipulated in four ways, with participants randomly allocated to corresponding groups-one that could see the objects (i.e., the control) and three that could not (i.e., the blind groups). To manipulate disease risk interpretation of the objects, labelling was used on the blind groups, with one receiving Disgust-Labels, one True-Labels and one no labels. Disgust was strongly associated with sticky and wet textures, and moderately with viscous, cold, and lumpy textures, suggesting adherence-to-skin may predict disgust. The participants in the disgust-labelled condition had the highest disgust ratings, and this was mediated by their increased sickness belief and fear of the objects. Object identification was poor when labels or visual cues were absent. Our findings suggest that tactile disgust may reflect a bottom-up sensory component-skin adhesion-moderated by judgements of disease-related threat.

Lessons of synaesthesia for consciousness: Learning from the exception, rather than the general

The question of whether the mechanisms underlying synaesthesia are similar to those ones underlying widespread cases of multisensory interactions tends to overshadow the question of whether their manifestations can be thought of as being continuous with one another. Here we focus on the conscious manifestations of synaesthesia and crossmodal correspondences and consider the dimensions along which these could be organised on a continuum. While synaesthesia and crossmodal correspondences may differ regarding the degree of vividness, frequency, specificity of the conscious manifestation, and control over its content, we demonstrate that these dimensions fail to lead to the expected continuous distribution. We suggest that the traditional distinction between conscious and non-conscious conditions might not be sufficient to separate synaesthesia from crossmodal correspondences, but highlight that the conscious manifestations that characterize synaesthesia remain exceptional and cannot be reconciled with other occasional occurrences of crossmodal mental imagery documented in the case of crossmodal correspondences.

Tactile roughness perception in the presence of olfactory and trigeminal stimulants

Previous research has shown that odorants consistently evoke associations with textures and their tactile properties like smoothness and roughness. Also, it has been observed that olfaction can modulate tactile perception. We therefore hypothesized that tactile roughness perception may be biased towards the somatosensory connotation of an ambient odorant. We performed two experiments to test this hypothesis. In the first experiment, we investigated the influence of ambient chemosensory stimuli with different roughness connotations on tactile roughness perception. In addition to a pleasant odor with a connotation of softness (PEA), we also included a trigeminal stimulant with a rough, sharp or prickly connotation (Ethanol). We expected that—compared to a No-odorant control condition—tactile texture perception would be biased towards smoothness in the presence of PEA and towards roughness in the presence of Ethanol. However, our results show no significant interaction between chemosensory stimulation and perceived tactile surface roughness. It could be argued that ambient odors may be less effective in stimulating crossmodal associations, since they are by definition extraneous to the tactile stimuli. In an attempt to optimize the conditions for sensory integration, we therefore performed a second experiment in which the olfactory and tactile stimuli were presented in synchrony and in close spatial proximity. In addition, we included pleasant (Lemon) and unpleasant (Indole) odorants that are known to have the ability to affect tactile perception. We expected that tactile stimuli would be perceived as less rough when simultaneously presented with Lemon or PEA (both associated with softness) than when presented with Ethanol or Indole (odors that can be associated with roughness). Again, we found no significant main effect of chemosensory condition on perceived tactile roughness. We discuss the limitations of this study and we present suggestions for future research.

Crossmodal correspondences between odors and contingent features: odors, musical notes, and geometrical shapes

Olfactory experiences represent a domain that is particularly rich in crossmodal associations. Whereas associations between odors and tastes, or other properties of their typical sources such as color or temperature, can be straightforwardly explained by associative learning, other matchings are much harder to explain in these terms, yet surprisingly are shared across individuals: The majority of people, for instance, associate certain odors and auditory features, such as pitch (Belkin, Martin, Kemp, & Gilbert, Psychological Science 8:340-342, 1997; Crisinel & Spence, Chemical Senses 37:151-158, 2012b) or geometrical shapes (Hanson-Vaux, Crisinel, & Spence, Chemical Senses 38:161-166, 2013; Seo, Arshamian, et al., Neuroscience Letters 478:175-178, 2010). If certain odors might indeed have been encountered while listening to certain pieces of music or seeing certain geometrical shapes, these encounters are very unlikely to have been statistically more relevant than others; for this reason, associative learning from regular exposure is ruled out, and thus alternative explanations in terms of metaphorical mappings are usually defended. Here we argue that these associations are not primarily conceptual or linguistic, but are grounded in structural perceptual or neurological determinants. These cases of crossmodal correspondences established between contingent environmental features can be explained as amodal, indirect, and transitive mappings across modalities. Surprising associations between odors and contingent sensory features can be investigated as genuine cases of crossmodal correspondences, akin to other widespread cases of functional correspondences that hold, for instance, between auditory and visual features, and can help reveal the structural determinants weighing on the acquisition of these crossmodal associations.

Object concepts in the chemical senses

This paper examines the applicability of the object concept to the chemical senses, by evaluating them against a set of criteria for object-hood. Taste and chemesthesis do not generate objects. Their parts, perceptible from birth, never combine. Orthonasal olfaction (sniffing) presents a strong case for generating objects. Odorants have many parts yet they are perceived as wholes, this process is based on learning, and there is figure-ground segregation. While flavors are multimodal representations bound together by learning, there is no functional need for flavor objects in the mouth. Rather, food identification occurs prior to ingestion using the eye and nose, with the latter retrieving multimodal flavor objects via sniffing (e.g., sweet smelling caramel). While there are differences in object perception between vision, audition, and orthonasal olfaction, the commonalities suggest that the brain has adopted the same basic solution when faced with extracting meaning from complex stimulus arrays.