The effect of multisensory context and experience on flavor preference decisions in rats

Flavor is perceived through multiple senses, including gustation and olfaction. Previous studies have shown that different sensory qualities that make up flavor are integrated to inform perceptual judgements. Psychophysical work in humans further suggests a prominent role for congruency (i.e., the learnt correspondence between taste and odor components of flavor through eating experience) in shaping multisensory interactions underlying perceptual judgments of flavor. However, eating experience cannot be controlled in humans, and depending on the type of judgement, these studies yielded mixed findings. Here, we used rats to test how experimentally-controlled experience with specific flavor mixtures (OdorA+TasteA and OdorB +TasteB) from weaning to adulthood affects subsequent flavor preference judgements in a series of two-bottle preference tests. In unisensory conditions, animals made odor or taste preference decisions (i.e., OdorA versus OdorB and TasteA versus TasteB, respectively). In multisensory conditions, animals made identical decisions, but the addition of the other modality rendered one solution congruent; the other one incongruent (e.g., OdorA+TasteA versus OdorB+TasteA). The results show that animals effectively learned congruency associations between the taste and smell components of experienced flavor mixtures. Comparing unisensory and multisensory conditions revealed no systematic effect of congruency on the magnitude of flavor preference, but preferences were less variable in multisensory compared to unisensory conditions. Results from a second group of naïve animals further demonstrate that increased reliability of preference judgements in multisensory conditions was independent of experience.

The role of the mediodorsal thalamus in chemosensory preference and consummatory behavior in rats

Experience plays a pivotal role in determining our food preferences. Consuming food generates odor-taste associations that shape our perceptual judgements of chemosensory stimuli, such as their intensity, familiarity, and pleasantness. The process of making consummatory choices relies on a network of brain regions to integrate and process chemosensory information. The mediodorsal thalamus is a higher-order thalamic nucleus involved in many experience-dependent chemosensory behaviors, including olfactory attention, odor discrimination, and the hedonic perception of flavors. Recent research has shown that neurons in the mediodorsal thalamus represent the sensory and affective properties of experienced odors, tastes, and odor-taste mixtures. However, its role in guiding consummatory choices remains unclear. To investigate the influence of the mediodorsal thalamus in the consummatory choice for experienced odors, tastes, and odor-taste mixtures, we pharmacologically inactivated the mediodorsal thalamus during 2-bottle brief-access tasks. We found that inactivation altered the preference for specific odor-taste mixtures, significantly reduced consumption of the preferred taste and increased within-trial sampling of both chemosensory stimulus options. Our results show that the mediodorsal thalamus plays a crucial role in consummatory decisions related to chemosensory preference and attention.

Orthonasal olfactory influences on consumer food behaviour

It is often suggested in the popular press that food chains deliberately introduce enticing product aromas into (and in the immediate vicinity of) their premises in order to attract customers. However, despite the widespread use of odours in the field of sensory marketing, laboratory research suggests that their effectiveness in modulating people's food behaviours depends on a range of contextual factors. Given the evidence that has been published to date, only under a subset of conditions is there likely to be a measurable effect of the presence of ambient odours on people's food attitudes and choices. This narrative historical review summarizes the various ways in which food odours appear to bias people's food preferences (appetite) and food choices (food consumption and purchase). Emphasis is placed on those experimental studies that have been designed to investigate how the characteristics of the olfactory stimuli (e.g., the congruency between the olfactory cues and the foods, intensity and duration of exposure to odours, and taste properties of odours) modulate the effects of olfactory cues on food behaviour. The review also explores the moderating roles of individual differences, such as dietary restraint, Body Mass Index (BMI), genetic and cultural differences in odour sensitivity and perception. Ultimately, following a review of empirical studies on food-related olfaction, current approaches in scent marketing are discussed and a research agenda is proposed to help encourage further studies on the effective application of scents in promoting healthy foods.

Multisensory integration of orally-sourced gustatory and olfactory inputs to the posterior piriform cortex in awake rats

Flavour refers to the sensory experience of food, which is a combination of sensory inputs sourced from multiple modalities during consumption, including taste and odour. Previous work has demonstrated that orally-sourced taste and odour cues interact to determine perceptual judgements of flavour stimuli, although the underlying cellular- and circuit-level neural mechanisms remain unknown. We recently identified a region of the piriform olfactory cortex in rats that responds to both taste and odour stimuli. Here, we investigated how converging taste and odour inputs to this area interact to affect single neuron responsiveness ensemble coding of flavour identity. To accomplish this, we recorded spiking activity from ensembles of single neurons in the posterior piriform cortex (pPC) in awake, tasting rats while delivering taste solutions, odour solutions and taste + odour mixtures directly into the oral cavity. Our results show that taste and odour inputs evoke highly selective, temporally-overlapping responses in multisensory pPC neurons. Comparing responses to mixtures and their unisensory components revealed that taste and odour inputs interact in a non-linear manner to produce unique response patterns. Taste input enhances trial-by-trial decoding of odour identity from small ensembles of simultaneously recorded neurons. Together, these results demonstrate that taste and odour inputs to pPC interact in complex, non-linear ways to form amodal flavour representations that enhance identity coding. KEY POINTS: Experience of food involves taste and smell, although how information from these different senses is combined by the brain to create our sense of flavour remains unknown. We recorded from small groups of neurons in the olfactory cortex of awake rats while they consumed taste solutions, odour solutions and taste + odour mixtures. Taste and smell solutions evoke highly selective responses. When presented in a mixture, taste and smell inputs interacted to alter responses, resulting in activation of unique sets of neurons that could not be predicted by the component responses. Synergistic interactions increase discriminability of odour representations. The olfactory cortex uses taste and smell to create new information representing multisensory flavour identity.

Variables influencing conditioning-evoked hallucinations: overview and future applications

Hallucinations occur in the absence of sensory stimulation and result in vivid perceptual experiences of nonexistent events that manifest across a range of sensory modalities. Approaches from the field of experimental and cognitive psychology have leveraged the idea that associative learning experiences can evoke conditioning-induced hallucinations in both animals and humans. In this review, we describe classical and contemporary findings and highlight the variables eliciting these experiences. We also provide an overview of the neurobiological mechanisms, along with the associative and computational factors that may explain hallucinations that are generated by representation-mediated conditioning phenomena. Through the integration of animal and human research, significant advances into the psychobiology of hallucinations are possible, which may ultimately translate to more effective clinical applications.

Beyond aroma: A scoping review on the impact of chronic rhinosinusitis on retronasal olfaction

Background

Retronasal olfaction (RNO) refers to the perception of odorants inhaled through the mouth and carried through the nasopharynx to olfactory receptors within the olfactory cleft, enabling the perception of flavor. Although orthonasal olfactory dysfunction in chronic rhinosinusitis (CRS) has been widely described, the impact of CRS on RNO is less clear. In this study, we systematically review available literature to provide an update on RNO in the setting of CRS.

Methods

We systematically searched PubMed, Ovid Embase, Web of Science, and the Cochrane Library for studies examining RNO in patients with documented CRS. The primary outcome of interest was objective psychophysical measurement of olfaction, including characterization of RNO.

Results

We identified 404 unique references that underwent title and abstract review by two independent reviewers, with 52 articles undergoing full-text review, where 10 relevant studies underwent data extraction. Although outcome measures varied, all included studies demonstrated diminished RNO in patients with CRS. Of six studies evaluating the relationship between retronasal and orthonasal olfactory test scores in CRS patients two out of six (33%) demonstrated a correlation between both forms of olfaction and CRS, and two out of six studies (33%) found significantly lower orthonasal olfactory test scores compared to retronasal olfactory test scores. Two of three found significant improvement in RNO with treatment of underlying CRS. Of three studies examining patient reported outcome measures (PROMs) in CRS, two found significant associations between retronasal olfactory test scores and PROMs.

Conclusions

Based on the current literature, CRS patients appear to have diminished RNO, which may be associated with orthonasal olfactory dysfunction and decreased quality of life in this population. Higher level of evidence studies are required to further elucidate these relationships and the impact of medical and surgical CRS management on RNO.

Exploring Group Differences in the Crossmodal Correspondences

There has been a rapid growth of interest amongst researchers in the cross-modal correspondences in recent years. In part, this has resulted from the emerging realization of the important role that the correspondences can sometimes play in multisensory integration. In turn, this has led to an interest in the nature of any differences between individuals, or rather, between groups of individuals, in the strength and/or consensuality of cross-modal correspondences that may be observed in both neurotypically normal groups cross-culturally, developmentally, and across various special populations (including those who have lost a sense, as well as those with autistic tendencies). The hope is that our emerging understanding of such group differences may one day provide grounds for supporting the reality of the various different types of correspondence that have so far been proposed, namely structural, statistical, semantic, and hedonic (or emotionally mediated).

The Enhancement of the Perception of Saltiness by Odorants Selected from Chinese Douchi in Salt Solution

Douchi is a traditional fermented soya bean product that is popular for its smelled saltiness and unique flavor. In order to look for the relationship between smelled saltiness of volatiles and their saltiness-enhancing properties, gas chromatography-olfactometry/associated taste was used to select odorants associated with saltiness in Yongchuan Douchi. The enhancement effects of saltiness intensity by selected odorants were further verified by sensory evaluation analyses of 2-alternative forced-choice and odor-induced saltiness enhancement in a follow-up study. A total of 14 odorant compounds were selected for their odor-associated saltiness perception. The compounds of 2-ethyl-3,5-dimethyl pyrazine, 2,5-dimethyl pyrazine, dimethyl trisulfide, 3-(methylthio) propanol and 3-(methylthio) propanal could significantly enhance saltiness perception in salt solution. Among them, 2-ethyl-3,5-dimethyl pyrazine was reported for the first time to be able to improve the salty taste. The study suggested that salty food is an ideal material for selecting saltiness-enhancing odorants, which could provide more direct theoretical support for salt reduction in the food industry.

Visual cues associated with sweet taste increase short-term eating and grab attention in healthy volunteers

Most studies that examine responses to food cues use images of actual foods as stimuli. Since foods are rewarding in multiple ways, it then becomes difficult to try and partial out the role of the importance of different aspects of food reward. Here we aimed to evaluate the impact of novel visual cues specifically associated with the immediate sensory reward from a liked sweet taste. In the training phase, one visual cue (CSsweet) was associated with the experience of sweet taste (10%sucrose) and a second, control cue (CSneutral) with a neutral taste (artificial saliva) using a disguised training procedure. In Experiment 1, participants (n = 45) were given an ad libitum snack intake test 30 min post-training, either labelled with CSsweet or CSneutral. Total caloric consumption was significantly higher in the CSsweet (650 ± 47 kcal) than CSneutral (477 ± 45 kcal) condition, but ratings of liking for the snacks did not differ significantly between conditions. In Experiment 2, participants (n = 80) exhibited an overall attentional bias (22.1 ± 9.9 ms) for the CSsweet relative to CSneutral cue (assessed using a dot-probe task), however rated liking for the CSsweet did not change significantly after cue-sweet training. Likewise, measures of expected satiety for drinks labelled with CSsweet did not differ significantly from CSneutral. Overall these two experiments provide evidence that associations between neutral visual cues and the experience of a liked sweet taste leads to cue-potentiated eating in the presence of the CSsweet cue. With no evidence that cue-sweet training altered rated liking for the visual cues, and in keeping with extant literature on the dissociation of hedonic and rewarding properties of food rewards, we propose this potentiation effect to reflect increased incentive salience.

Odor-Taste-Texture Interactions as a Promising Strategy to Tackle Adolescent Overweight

The adolescence period is characterized by a considerable risk to weight gain due to the high consumption of food rich in sugar. A promising strategy to reduce sugar consumption may lie in exploiting the ability of our senses to interact to each other (cross-modal interactions). The aims were to investigate the cross-modal interactions and gustatory function in normal-weight and overweight adolescents. Fifty adolescents (25 overweight and 25 normal-weight) were involved. Subjects rated liking and attribute intensity in pudding samples obtained by adding vanilla aroma (0.1%; 0.3%), butter aroma (0.05%; 0.1%) or a thickener agent (1%; 1.5%) to a base formulation. The gustatory function was also measured through the “taste strips” methodology. Overweight adolescents were found to have a significantly (p < 0.001) worse ability to correctly identify all tastes. Cross-modal interactions occurred differently according to their body mass index, with a significant increase (p < 0.05) in sensory desirable characteristics (e.g., sweet and creaminess) due to aroma addition, especially in overweight subjects. Furthermore, butter aroma significantly increased hedonic responses only in overweight subjects. Tricking our senses in the way of perceiving sensory attributes could be a promising strategy to develop innovative food formulations with a reduced sugar amount, which will lead to a potential decrease in caloric intake and help to tackle the obesity epidemic.

What Is the Relationship between the Presence of Volatile Organic Compounds in Food and Drink Products and Multisensory Flavour Perception?

This narrative review examines the complex relationship that exists between the presence of specific configurations of volatile organic compounds (VOCs) in food and drink products and multisensory flavour perception. Advances in gas chromatography technology and mass spectrometry data analysis mean that it is easier than ever before to identify the unique chemical profile of a particular food or beverage item. Importantly, however, there is simply no one-to-one mapping between the presence of specific VOCs and the flavours that are perceived by the consumer. While the profile of VOCs in a particular product undoubtedly does tightly constrain the space of possible flavour experiences that a taster is likely to have, the gustatory and trigeminal components (i.e., sapid elements) in foods and beverages can also play a significant role in determining the actual flavour experience. Genetic differences add further variation to the range of multisensory flavour experiences that may be elicited by a given configuration of VOCs, while an individual’s prior tasting history has been shown to determine congruency relations (between olfaction and gustation) that, in turn, modulate the degree of oral referral, and ultimately flavour pleasantness, in the case of familiar foods and beverages.

Components Associated With Saltiness Potentiation in Frankfurters Made With Traditionally Brewed Soy Sauce

Salt is a critical ingredient in processed meat and poultry products because of its multiple functions that affect product quality and safety. Although salt is a functional ingredient in food products, sodium reduction continues to be an important topic within the food industry due to interests in reducing dietary sodium intake. Previous work has shown that soy sauce addition may potentiate saltiness perception in processed meats and thus allow for novel formulations with reduced sodium content. Two studies were conducted to further elucidate these effects. First, trained panel sensory char- acteristics, relevant quality parameters, and selected chemical profiles were determined comparing frankfurters containing flake salt and traditionally brewed soy sauce. Seven aqueous compounds were found to be more abundant (P &lt; 0.001) in the soy sauce – containing treatment, and 56 volatile compounds were identified. Principal component analysis of the sensory and selected chemical profiles led to the consideration that ethyl hexanoate (EHEX) may be a causative agent of the saltiness-potentiating phenomenon. Thus, a second study further evaluated concentrations of EHEX, revealing that trained sensory panelists perceived frankfurters containing EHEX as saltier (P &lt; 0.05) and these frankfurters had higher scores for fermented/sour aromatic score (P &lt; 0.05) than the control (Control: 100% NaCl from flake salt). This research demon- strated the ability of EHEX to potentiate saltiness in frankfurters with minimal effects on quality.

Multisensory interactions underlying flavor consumption in rats: the role of experience and unisensory component liking

The mechanisms by which taste and odor are combined in determining food choice behavior are poorly understood. Previous work in human subjects has yielded mixed results, potentially due to differences in task context across studies, and a lack of control over flavor experience. Here, we used rats as a model system to systematically investigate the role of experience and unisensory component liking in the multisensory interactions underlying consumption behavior. We demonstrate that taste–smell mixture consumption is best explained by a linear average of component liking. The observed pattern of results was not dependent on prior experience with specific taste–smell combinations, and unique for multisensory as opposed to unisensory mixture consumption. The results are discussed with respect to existing models of flavor integration, and a maximum-likelihood integration model previously described for multisensory judgments in other systems.

Configural memory of a blending aromatic mixture reflected in activation of the left orbital part of the inferior frontal gyrus

Blending aromatic mixtures components naturally fuse to form a unique odor - a configuration- qualitatively different from each component's odor. Repeated exposure to the components either in the mixture or separately, favors respectively, configural and elemental processings. The neural bases of such processes are still unknown. We examined the brain correlates of the experienced-induced configural processing of a well-known model of binary blending odor mixture, the aromatic pineapple blending (AB, ethyl maltol + ethyl isobutyrate). Before fMRI recording, half of the participants were repeatedly exposed to the mixture (AB, group Gmix), with the other half exposed to its separate components (A and B; Gcomp). During the fMRI recording, all participants were stimulated with the mixture (AB) and the components (A and B). Finally, participants rated the number of odors perceived for each stimulus. Gmix perceived the AB mixture as less complex than did Gcomp. While Gcomp perceived the mixture as more complex than its components, Gmix did not. These results show the presence of experience-induced configural or elemental processing of the AB mixture in each group. Contrasting the brain activity of Gcomp and Gmix, when stimulated with AB, revealed higher activation in the left orbital part of the inferior frontal gyrus. This result sheds light on this area's function, commonly found activated in olfactory studies, and closely connected with the lateral orbitofrontal cortex. We discuss the role of this area as a mediator of configural percepts between temporal and orbitofrontal areas involved in configural memory processes.

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.

Adaptive weighting of taste and odor cues during flavor choice

Colloquially referred to as "taste," flavor is in reality a thoroughly multisensory experience. Yet, a mechanistic understanding of the multisensory computations underlying flavor perception and food choice is lacking. Here, we used a multisensory flavor choice task in rats to test specific predictions of the statistically optimal integration framework, which has previously yielded much insight into cue integration in other multisensory systems. Our results confirm three key predictions of this framework in the unique context of flavor choice behavior, providing novel mechanistic insight into multisensory flavor processing.NEW & NOTEWORTHY The authors demonstrate that rats make choices about which flavor solution (i.e., taste-odor mixture) to consume by weighting the individual taste and odor components according to the reliability of the information they provide about which solution is the preferred one. A similar weighting operation underlies multisensory cue combination in other domains and offers novel insight into the computations underlying multisensory flavor perception and food choice behavior.

Characteristics of Olfactory Disorder With and Without Reported Flavor Loss

OBJECTIVES/HYPOTHESIS

Quality of life related to olfactory disorder (OD) depends on the perceived impairment. It is not known why some patients with OD report smell and flavor loss while others report smell loss only. In order to understand this, we compared the two clinical presentation forms in terms of demographics, clinical features, and orthonasal olfaction test results.

STUDY DESIGN

Observational, analytic, cross-sectional study.

METHODS

A total of 401 patients with measured orthonasal OD presenting at a tertiary referral center were divided in 2 groups according to their subjective reports (smell loss only = 129 patients vs. smell and flavor loss = 272 patients). Groups were compared in terms of demographic (age, sex), clinical features (duration of disease, type of onset, etiology, degree of impairment due to the disorder) and test results (taste and orthonasal olfaction).

RESULTS

Groups did not differ in terms of age, sex distribution, orthonasal olfactory, or taste function. Patients reporting smell and flavor loss were characterized by a mainly sudden onset of the disorder and a predominance of postinfectious olfactory loss. They also have a shorter disease duration and a higher disease impairment. For patients reporting smell loss only, disease duration is longer, they feel less impaired, the onset of the disorder is to a higher degree protracted and the main cause is idiopathic.

CONCLUSIONS

Patients with orthonasal OD reporting smell and flavor loss feel more impaired and present significant different clinical features compared to patients reporting smell loss only. Future studies measuring retronasal olfaction are necessary to fully understand flavor perception in OD.

LEVEL OF EVIDENCE

4 Laryngoscope, 130:2869-2873, 2020.

Impact of Bottle Aging on the Composition and Sensory Properties of Flavored Chardonnay and Shiraz Wines

Natural flavorings could potentially be used to enhance the intensity of wine aroma and flavor; albeit since flavor additives are not legally permitted winemaking aids, flavored wines would need to be labeled as wine products. In this study, changes in the composition and sensory profiles of flavored Chardonnay (n = 2) and Shiraz (n = 2) wines were compared at bottling, and then again after 12 months of bottle aging. Flavorings and flavored wines were also analyzed by gas chromatography-mass spectrometry (GC-MS) to determine the key constituents responsible for changes to aroma and flavor profiles. However, many of the volatile compounds identified in flavor additives were not detected at appreciably higher concentrations in flavored wines, which was attributed to the very small quantities of flavorings that were added to base wines. The sensory profiles of control and flavored wines were determined by descriptive analysis, and the addition of flavorings to base wines significantly influenced the perception of some sensory attributes. Flavored Chardonnay wines exhibited enhanced fruit aromas and flavors, while fruit and developed attributes were enhanced in flavored Shiraz wines. Differences in sensory profiles were less apparent in Chardonnay wines following bottle aging, but depending on the flavorings added, flavored Shiraz wines could still be discriminated from their corresponding control wines after bottle aging. Results from this study demonstrate the potential for flavor additives to be used to enhance desirable attributes and/or mitigate wine sensory deficiencies.

Experience Informs Consummatory Choices for Congruent and Incongruent Odor-Taste Mixtures in Rats

Experience is an essential factor informing food choice. Eating food generates enduring odor-taste associations that link an odor with a taste's quality and hedonic value (pleasantness/unpleasantness) and creates the perception of a congruent odor-taste combination. Previous human psychophysical experiments demonstrate that experience with odor-taste mixtures shapes perceptual judgments related to the intensity, familiarity, and pleasantness of chemosensory stimuli. However, how these perceptual judgments inform consummatory choice is less clear. Using rats as a model system and a 2-bottle brief-access task, we investigated how experience with palatable and unpalatable odor-taste mixtures influences consummatory choice related to odor-taste congruence and stimulus familiarity. We found that the association between an odor and a taste, not the odor's identity or its congruence with a taste, informs consummatory choice for odor-taste mixtures. Furthermore, we showed that the association between an odor and a taste, not odor neophobia, informs consummatory choice for odors dissolved in water. Our results provide further evidence that the association between an odor and a taste, after odor-taste mixture experience, is a fundamental feature guiding consummatory choice.

Individual Differences in Sweetness Ratings and Cross-Modal Aroma-Taste Interactions

Aroma-taste interactions, which are believed to occur due to previous coexposure (concurrent presence of aroma and taste), have been suggested as a strategy to aid sugar reduction in food and beverages. However, coexposures might be influenced by individual differences. We therefore hypothesized that aroma-taste interactions vary across individuals. The present study investigated how individual differences (gender, age, and sweet liker status) influenced the effect of aroma on sweetness intensity among young adults. An initial screening of five aromas, all congruent with sweet taste, for their sweetness enhancing effect was carried out using descriptive analysis. Among the aromas tested, vanilla was found most promising for its sweet enhancing effects and was therefore tested across three sucrose concentrations by 129 young adults. Among the subjects tested, females were found to be more susceptible to the sweetness enhancing effect of vanilla aroma than males. For males, the addition of vanilla aroma increased the sweet taste ratings significantly for the 22–25-year-olds, but not the 19–21-year-olds. Consumers were clustered according to their sweet liker status based on their liking for the samples. Although sweet taste ratings were found to vary with the sweet liker status, aroma enhanced the sweetness ratings similarly across clusters. These results call for more targeted product development in order to aid sugar reduction.

Retronasal olfactory function in patients with smell loss but subjectively normal flavor perception

OBJECTIVES

The human sense of smell constitutes the main part of flavor perception. Typically, patients with loss of olfactory function complain of diminished perception during eating and drinking. However, some patients with smell loss still report normal enjoyment of foods. The aim of the present study was to compare orthonasal and retronasal olfactory function in patients with non-sinonasal smell loss and subjectively normal flavor perception.

METHODS

Nineteen patients (mean age [range] 52.0 [8-83 years]) with self-reported olfactory impairment but subjective normal flavor perception were included. Olfactory performance was assessed using the Sniffin' Sticks (TDI) for orthonasal and the Candy Smell Test (CST) for retronasal function. Visual analogue scales were used for self-assessment of odor (SOP), taste (STP), and flavor perception (SFP), ranging from 0 (no perception) to 10 (excellent perception).

RESULTS

Mean (SD) SFP was 8.0 (1.8). Mean (SD) orthonasal TDI-score of all patients was 14.4 (5.3, range 6-25.3) with 11 patients classified as anosmic and eight as hyposmic. Mean/SD retronasal CST-score was 8.8 (2.7, range 3-13) within the range of anosmia/hyposmia. No correlation was found between SFP and the CST (P = .62).

CONCLUSION

The present results showed that despite claiming normal flavor perception, our patients were ortho- and retronasally dysosmic using standard tests for olfactory function. Although other explanations could be possible, we suggest that this subjective flavor perception might be due to unconscious memory recall from previously experienced cross-modal sensory interactions.

LEVEL OF EVIDENCE

4 Laryngoscope, 130:1629-1633, 2020.

Vanillin modifies affective responses to but not burning sensations from ethanol in mixtures

Vanillin may modulate perception of noxious oral stimuli via TRP receptor interactions; separately, vanillin has also been shown to have top-down influences on flavor perception. Here, we ask whether added vanillin decreases the perceived burn of ethanol either via peripheral or cognitive mechanisms. Participants rated the burn of ethanol with 0, 16, and 160 ppm vanillin. In studies 1 (n = 102) and 2 (n = 82), participants wore nose clips and rated the burn of 8% and 16% ethanol (study 1) or 32% and 48% ethanol (study 2). In study 3 (n = 65), participants were able to breathe freely and rated liking and perceptual qualities of 8% and 32% ethanol at each vanillin level. Vanillin showed no significant effect on ratings of burn or smoothness, but did increase perceived sweetness (p < .001) and liking (p = .004) in study 3. These data suggest vanillin does not modulate ethanol burn via TRP receptor mediated interactions, but may shift hedonic responses to ethanol via top-down processes.

Interactions of Lemon, Sucrose and Citric Acid in Enhancing Citrus, Sweet and Sour Flavors

Flavorants such as lemon extract that activate olfactory receptors may also evoke or enhance flavor qualities such as sour and sweet that are typically considered gustatory. Similarly, flavorants such as sucrose and citric acid that activate gustatory receptors may enhance flavors such as citrus that are typically considered olfactory. Here, we ask how lemon extract, sucrose, and citric acid, presented separately and together, affect sweet, sour, and citrus flavors. We accomplished this by testing, in the same 12 subjects, lemon extract and sucrose (Experiment 1), lemon extract and citric acid (Experiment 2), and lemon extract, sucrose, and citric acid (Experiment 3). Results showed that both lemon extract and citric acid increased the ratings of citrus and sour intensity. Lemon extract did not affect sweet, but citric acid did, mainly in Experiment 3. Sucrose systematically increased only sweet intensity and modulated the effect of lemon extract on sour. The most robust multiquality effect was the enhancement of sour by lemon extract. These outcomes suggest, first, a role played by experience with the statistical associations of gustatory and olfactory flavorants and, second, that lemon flavor is complex, having citrus and sour qualities that may not be fully separable in perception.

Experience-dependent c-Fos expression in the primary chemosensory cortices of the rat

Eating a new food is a unique event that guides future food choices. A key element for these choices is the perception of flavor (odor-taste associations), a multisensory process dependent upon taste and smell. The two primary cortical areas for taste and smell, gustatory cortex and piriform cortex, are thought to be crucial regions for processing and responding to odor-taste mixtures. To determine how previous experience impacts the primary chemosensory cortices, we compared the expression of the immediate early gene, c-Fos, between rats presented with a taste, an odor, or an odor-taste mixture for the first-time with rats that had many days of prior experience. Compared to rats with prior experience, we found that first-time sampling of all three chemosensory stimuli led to significantly greater c-Fos expression in gustatory cortex. In piriform cortex, only the novel chemosensory stimuli containing odors showed greater c-Fos expression. These results indicate that prior experience with taste, odor, or odor-taste stimuli habituates responses in the primary chemosensory cortices and adds further evidence supporting gustatory cortex as a fundamental node for the integration of gustatory and olfactory signals.

Multisensory flavor perception: The relationship between congruency, pleasantness, and odor referral to the mouth

Our hedonic response to a food is determined by its flavor, an inherently multisensory experience that extends beyond the mere addition of its odor and taste. While congruency is known to be important for multisensory processes in general, little is known about its specific role in flavor processing. The aim of the present study was to delineate the effects of odor-taste congruency on two central aspects of flavor: odor referral (or mislocalization) to the mouth, and pleasantness. We further aimed to test whether an eventual effect on pleasantness was mediated by odor referral. Aqueous solutions containing odors and tastes were prepared to create food-like stimuli with varying degrees of congruency, ranging from maximally incongruent to maximally congruent in nine steps. Thirty participants reported where they perceived the odors, and how much they liked the solutions. Congruency had a positive linear effect both on odor referral to the oral cavity and on pleasantness. However, the effect of congruency on pleasantness was not mediated by odor referral. These results indicate that as an odor-taste mixture approximates a mental representation of a familiar food, its components are increasingly merged into one perceptual object sensed in the mouth. In parallel, the mixture is evaluated as increasingly pleasant, which promotes consumption of familiar foods that have been determined through experience to be non-toxic. While the modulatory role of congruency on pleasantness and odor referral was confirmed, our results also indicate that these effects arise through distinct perceptual mechanisms.

Successful differential evaluative conditioning using simultaneous and trace conditioning procedures in the picture–picture paradigm

This paper describes a study designed to investigate the efficacy of two traditional classical conditioning procedures in generating evaluative conditioning (EC) in the picture–picture paradigm in human participants. Differential EC was found using both simultaneous and trace conditioning procedures. In addition, the use of a block–subblock (BSB) nonpaired control condition and full counterbalancing of conditioned stimulus–unconditioned stimulus (CS–UCS) pairings across participants indicated that the observed EC effects were the result of associative learning. Examination of whether successful conditioning could take place with or without conscious awareness of CS–UCS contingencies was inconclusive. The results provide evidence for EC as an associative process and also provide some insight into the possible conditioning parameters that might successfully generate EC.

Relative Contribution of Odour Intensity and Valence to Moral Decisions

Meta-analytic evidence showed that the chemical senses affect moral decisions. However, how odours impact on morality is currently unclear. Through a set of three studies, we assess whether and how odour intensity biases moral choices (Study 1a), its psychophysiological responses (Study 1b), as well as the behavioural and psychophysiological effects of odour valence on moral choices (Study 2). Study 1a suggests that the presence of an odour plays a role in shaping moral choice. Study 1b reveals that of two iso-pleasant versions of the same neutral odour, only the one presented sub-threshold (vs. supra-threshold) favours deontological moral choices, those based on the principle of not harming others even when such harm provides benefits. As expected, this odour intensity effect is tracked by skin conductance responses, whereas no difference in cardiac activity - proxy for the valence dimension - is revealed. Study 2 suggests that the same neutral odour presented sub-threshold increases deontological choices even when compared to iso-intense ambiguous odour, perceived as pleasant or unpleasant by half of the participants, respectively. Skin conductance responses, as expected, track odour pleasantness, but cardiac activity fails to do so. Results are discussed in the context of mechanisms alternative to disgust induction underlying moral choices.

Model cheese aroma perception is explained not only by in vivo aroma release but also by salivary composition and oral processing parameters

The aim of the present paper was to determine, from four model cheeses differing in fat content and firmness, the respective impacts ofin vivoaroma release, bolus rheology, chewing activity, mouth coating and salivary composition on dynamic aroma perception.

Single-neuron responses to intraoral delivery of odor solutions in primary olfactory and gustatory cortex

Smell plays a major role in our perception of food. Odorants released inside the mouth during consumption are combined with taste and texture qualities of a food to guide flavor preference learning and food choice behavior. Here, we built on recent physiological findings that implicated primary sensory cortex in multisensory flavor processing. Specifically, we used extracellular recordings in awake rats to characterize responses of single neurons in primary olfactory (OC) and gustatory cortex (GC) to intraoral delivery of odor solutions and compare odor responses to taste and plain water responses. The data reveal responses to olfactory, oral somatosensory, and gustatory qualities of intraoral stimuli in both OC and GC. Moreover, modality-specific responses overlap in time, indicating temporal convergence of multisensory, flavor-related inputs. The results extend previous work suggesting a role for primary OC in mediating influences of taste on smell that characterize flavor perception and point to an integral role for GC in olfactory processing.NEW & NOTEWORTHY Food perception is inherently multisensory, taking into account taste, smell, and texture qualities. However, the neural mechanisms underlying flavor perception remain unknown. Recording neural activity directly from the rat brain while animals consume multisensory flavor stimuli, we demonstrate that information about odor, taste, and mouthfeel of food converges on primary taste and smell cortex. The results suggest that processing of naturalistic, multisensory information involves an interacting network of primary sensory areas.

Odour Perception: An Object-Recognition Approach

Object recognition is a crucial component of both visual and auditory perception. It is also critical for olfaction. Most odours are composed of 10s or 100s of volatile components, yet they are perceived as unitary perceptual events against a continually shifting olfactory background (ie figure—ground segregation). We argue here that this occurs by rapid central adaptation to background odours combined with a pattern-matching system to recognise discrete sets of spatial and temporal olfactory features—an odour object. We present supporting neuropsychological, learning, and developmental evidence and then describe the neural circuitry which underpins this. The vagaries of an object-recognition approach are then discussed, with emphasis on the putative importance of memory, multimodal representations, and top—down processing.