Basic taste stimuli elicit unique responses in facial skin blood flow

Inducing Novel Sound-Taste Correspondences via an Associative Learning Task

The interest in crossmodal correspondences, including those involving sounds and involving tastes, has experienced rapid growth in recent years. However, the mechanisms underlying these correspondences are not well understood. In the present study (N = 302), we used an associative learning paradigm, based on previous literature using simple sounds with no consensual taste associations (i.e., square and triangle wave sounds at 200 Hz) and taste words (i.e., sweet and bitter), to test the influence of two potential mechanisms in establishing sound-taste correspondences and investigate whether either learning mechanism could give rise to new and long-lasting associations. Specifically, we examined an emotional mediation account (i.e., using sad and happy emoji facial expressions) and a transitive path (i.e., sound-taste correspondence being mediated by color, using red and black colored squares). The results revealed that the associative learning paradigm mapping the triangle wave tone with a happy emoji facial expression induced a novel crossmodal correspondence between this sound and the word sweet. Importantly, we found that this novel association was still present two months after the experimental learning paradigm. None of the other mappings, emotional or transitive, gave rise to any significant associations between sound and taste. These findings provide evidence that new crossmodal correspondences between sounds and tastes can be created by leveraging the affective connection between both dimensions, helping elucidate the mechanisms underlying these associations. Moreover, these findings reveal that these associations can last for several weeks after the experimental session through which they were induced.

Tasty vibes: Uncovering crossmodal correspondences between tactile vibrations and basic tastes

The interest in crossmodal correspondences individually involving the senses of touch and taste has grown rapidly in the last few decades. Several correspondences involving different tactile dimensions (e.g., hardness/softness, roughness/smoothness) have been uncovered, such as those between sweetness and softness and between roughness and sourness. However, a dimension that has been long overlooked, despite its pervasiveness and importance in everyday experiences, relates to tactile vibrations. The present study aimed to fill this gap and investigate crossmodal correspondences between basic tastes and vibrations. In the present study (N = 72), we uncovered these associations by having participants sample basic taste (i.e., sweet, salty, sour, bitter, umami) aqueous solutions and chose the frequency of vibrations, delivered via a consumer-grade subwoofer wristband on their dominant hand, that they most strongly associated with each taste. We found that sourness was most strongly associated with frequencies around 98 Hz, and that sweetness and umami were associated with frequencies around 77 Hz. These correspondences may, to different extents, be based on affective and semantic mechanisms. The findings have relevant implications for theoretical research on multisensory integration and perception and the potential future applications of these associations, through wearable technologies, to enhance eating experiences and promote healthier eating habits.

Predicting Perceived Hedonic Ratings through Facial Expressions of Different Drinks

Previous studies have established the utility of facial expressions as an objective assessment approach for determining the hedonics (overall pleasure) of food and beverages. This study endeavors to validate the conclusions drawn from preceding research, illustrating that facial expressions prompted by tastants possess the capacity to forecast the perceived hedonic ratings of these tastants. Facial expressions of 29 female participants, aged 18-55 years, were captured using a digital camera during their consumption of diverse concentrations of solutions representative of five basic tastes. Employing the widely employed facial expression analysis application FaceReader, the facial expressions were meticulously assessed, identifying seven emotions (surprise, happiness, scare, neutral, disgust, sadness, and anger) characterized by scores ranging from 0 to 1-a numerical manifestation of emotional intensity. Simultaneously, participants rated the hedonics of each solution, utilizing a scale spanning from -5 (extremely unpleasant) to +5 (extremely pleasant). Employing a multiple linear regression analysis, a predictive model for perceived hedonic ratings was devised. The model's efficacy was scrutinized by assessing emotion scores from 11 additional taste solutions, sampled from 20 other participants. The anticipated hedonic ratings demonstrated robust alignment and agreement with the observed ratings, underpinning the validity of earlier findings even when incorporating diverse software and taste stimuli across a varied participant base. We discuss some limitations and practical implications of our technique in predicting food and beverage hedonics using facial expressions.

Application of Augmented Reality in the Sensory Evaluation of Yogurts

Augmented reality (AR) applications in the food industry are considered innovative to enrich the interactions among consumers, food products, and context. The study aimed to investigate the effects of AR environments on the sensory responses of consumers towards different yogurts. AR HoloLens headsets were used to set up two AR environments: (1) AR coconut view (ARC) and (2) AR dairy view (ARD). Hedonic ratings, just-about-right (JAR), check-all-that-apply (CATA) attribute terms, emotional responses, purchase intent, and consumer purchasing behaviors of three types of yogurts (dairy-free coconut, dairy, and mixed) were measured under ARC, ARD, and sensory booths (SB). The results showed that the liking scores of dairy and mixed yogurts were generally higher than the coconut yogurt regardless of the environment. The interaction effect of yogurts and environments was statistically significant in terms of appearance, taste/flavor, sweetness, mouthfeel, aftertaste, and overall liking. JAR and penalty analysis revealed that consumers penalized the coconut yogurt for being “too much” in sourness, “too little” in sweetness, and “too thin” in mouthfeel. For the CATA analysis, attribute terms positively associated with overall liking (such as “sweet”, “smooth”, and “creamy”) were selected for dairy and mixed yogurts, whereas the attribute terms negatively associated with overall liking (such as “firm”, “heavy”, and “astringent”) were only selected for coconut yogurts. Regarding yogurt-consumption behaviors, the purchase intent of dairy and mixed yogurts was higher than that of the coconut yogurt, and taste and health were considered to be the most critical factors for yogurt consumption.

Taste Responses to Chocolate Pudding with Different Sucrose Concentrations through Physiological and Explicit Self-Reported Measures

The past few decades have seen significant methodological and theoretical change within sensory science, including in food sciences. The physiological reaction to the Autonomous Nervous System (ANS) provides insightful information in interpreting consumers’ sensory and affective reactions. In this regard, we investigated how explicit responses of liking and perceived intensity of sensory features (sweet, bitter, and astringency) and implicit objective physiological responses of Heart Rate (HR) and Galvanic Skin Response (GSR) are modulated when varying the sweetness (sucrose concentration with 38; 83; 119; 233 g/kg) level in a cocoa-based product (dark chocolate pudding) and their relationship. The demographic effects on responses were also investigated. Results showed the effects of the sucrose concentration levels on liking and perceived intensity of all the sensory characteristics and on HR responses, which highlighted a significant effect of the sucrose concentration level. As regards the relationship between variables, a significant positive effect was found for the sucrose concentration level 3, where an increase in HR leads to an increase in liking; for the perceived bitterness, a significant positive effect of HR for the sucrose concentration level 1; and for the perceived astringent, a significant positive effect of HR for the sucrose concentration level 2. While we found no significant main effect of gender on our dependent variables, the results highlight a significant main effect of age, increasing the adult population responses. The present research helps to understand better the relationship between explicit and implicit sensory study variables with foods. Furthermore, it has managerial applications for chocolate product developers. The level of sweetness that might be optimal to satisfy at the explicit level (liking) and the implicit level (HR or emotional valence) is identified.

Analysis of facial expressions in response to basic taste stimuli using artificial intelligence to predict perceived hedonic ratings

Taste stimuli can induce a variety of physiological reactions depending on the quality and/or hedonics (overall pleasure) of tastants, for which objective methods have long been desired. In this study, we used artificial intelligence (AI) technology to analyze facial expressions with the aim of assessing its utility as an objective method for the evaluation of food and beverage hedonics compared with conventional subjective (perceived) evaluation methods. The face of each participant (10 females; age range, 21–22 years) was photographed using a smartphone camera a few seconds after drinking 10 different solutions containing five basic tastes with different hedonic tones. Each image was then uploaded to an AI application to achieve outcomes for eight emotions (surprise, happiness, fear, neutral, disgust, sadness, anger, and embarrassment), with scores ranging from 0 to 100. For perceived evaluations, each participant also rated the hedonics of each solution from –10 (extremely unpleasant) to +10 (extremely pleasant). Based on these, we then conducted a multiple linear regression analysis to obtain a formula to predict perceived hedonic ratings. The applicability of the formula was examined by combining the emotion scores with another 11 taste solutions obtained from another 12 participants of both genders (age range, 22–59 years). The predicted hedonic ratings showed good correlation and concordance with the perceived ratings. To our knowledge, this is the first study to demonstrate a model that enables the prediction of hedonic ratings based on emotional facial expressions to food and beverage stimuli.

Silicon supplementation improves the nutritional and sensory characteristics of lentil seeds obtained from drought-stressed plants

BACKGROUND

Lentil is an important nutritionally rich pulse crop in the world. Despite having a prominent role in human health and nutrition, it is very unfortunate that global lentil production is adversely limited by drought stress, causing a huge decline in yield and productivity. Drought stress can also affect the nutritional profile of seeds. Silicon (Si) is an essential element for plants and a general component of the human diet found mainly in plant-based foods. This study investigated the effects of Si on nutritional and sensory properties of seeds obtained from lentil plants grown in an Si-supplied drought-stressed environment.

RESULTS

Significant enhancements in the concentration of nutrients (protein, carbohydrate, dietary fibre, Si) and antioxidants (ascorbate, phenol, flavonoids, total antioxidants) were found in seeds. Significant reductions in antinutrients (trypsin inhibitor, phytic acid, tannin) were also recorded. A novel sensory analysis was implemented in this study to evaluate the unconscious and conscious responses of consumers. Biometrics were integrated with a traditional sensory questionnaire to gather consumers responses. Significant positive correlations (R = 0.6-1) were observed between sensory responses and nutritional properties of seeds. Seeds from Si-treated drought-stressed plants showed higher acceptability scores among consumers.

CONCLUSION

The results demonstrated that Si supplementation can improve the nutritional and sensory properties of seeds. This study offers an innovative approach in sensory analysis coupled with biometrics to accurately assess a consumer's preference towards tested samples. In the future, the results of this study will help in making a predictive model for sensory traits and nutritional components in seeds using machine-learning modelling techniques. © 2020 Society of Chemical Industry.

Facial Blood Flow Responses to Dynamic Exercise

We reported previously that a static handgrip exercise evoked regional differences in the facial blood flow. The present study examined whether regional differences in facial blood flow are also evoked during dynamic exercise. Facial blood flow was measured by laser speckle flowgraphy during 15 min of cycling exercise at heart rates of 120 bpm, 140 bpm and 160 bpm in 12 subjects. The facial vascular conductance index was calculated from the blood flow and mean arterial pressure. The regional blood flow and conductance index values were determined in the forehead, eyelid, nose, cheek, ear and lip. One-way ANOVA and Tukey's post-hoc test were used to examine effects of exercise intensity and target regions. The blood flow and conductance index in skin areas increased significantly with the exercise intensity. The blood flow and conductance index in the lip increased significantly at 120 bpm and 140 bpm compared to the control, while the values in the lip at 160 bpm did not change from the control values. These results suggest that the blood flow in facial skin areas, not in the lip, responds similarly to dynamic exercise, in contrast to the responses to static exercise.

Automatic Facial Paralysis Assessment via Computational Image Analysis

Facial paralysis (FP) is a loss of facial movement due to nerve damage. Most existing diagnosis systems of FP are subjective, e.g., the House-Brackmann (HB) grading system, which highly depends on the skilled clinicians and lacks an automatic quantitative assessment. In this paper, we propose an efficient yet objective facial paralysis assessment approach via automatic computational image analysis. First, the facial blood flow of FP patients is measured by the technique of laser speckle contrast imaging to generate both RGB color images and blood flow images. Second, with an improved segmentation approach, the patient's face is divided into concerned regions to extract facial blood flow distribution characteristics. Finally, three HB score classifiers are employed to quantify the severity of FP patients. The proposed method has been validated on 80 FP patients, and quantitative results demonstrate that our method, achieving an accuracy of 97.14%, outperforms the state-of-the-art systems. Experimental evaluations also show that the proposed approach could yield objective and quantitative FP diagnosis results, which agree with those obtained by an experienced clinician.

Physiological Responses to Basic Tastes for Sensory Evaluation of Chocolate Using Biometric Techniques

Facial expressions are in reaction to basic tastes by the response to receptor stimulation. The objective of this study was to assess the autonomic nervous system responses to basic tastes in chocolates and to identify relationships between conscious and unconscious responses from participants. Panelists (n = 45) tasted five chocolates with either salt, citric acid, sugar, or monosodium glutamate, which generated four distinctive basic tastes plus bitter, using dark chocolate. An integrated camera system, coupled with the Bio-Sensory application, was used to capture infrared thermal images, videos, and sensory responses. Outputs were used to assess skin temperature (ST), facial expressions, and heart rate (HR) as physiological responses. Sensory responses and emotions elicited during the chocolate tasting were evaluated using the application. Results showed that the most liked was sweet chocolate (9.01), while the least liked was salty chocolate (3.61). There were significant differences for overall liking (p < 0.05) but none for HR (p = 0.75) and ST (p = 0.27). Sweet chocolate was inversely associated with angry, and salty chocolate positively associated with sad. Positive emotion-terms were associated with sweet samples and liking in self-reported responses. Findings of this study may be used to assess novel tastes of chocolate in the industry based on conscious and emotional responses more objectively.

Regional differences in facial skin blood flow responses to thermal stimulation

PURPOSE

The facial skin blood flow (SkBF) shows regional differences in the responses to a given stimulation. The facial SkBFs, especially in the eyelid and nose exhibit unique response to physiological and psychological stimuli, but the mechanisms inducing those regional differences remain unclear. To investigate whether the regional differences in the local control of vasomotion in facial vessels correspond to the regional differences in facial SkBF response, we monitored the relative change of facial SkBF to regional thermal stimulation. We hypothesized that heat stimulation dilates the cutaneous vessels in the eyelid, while cold stimulation constricts those in the nose, which was based on previous findings METHODS: A thermal stimulator was used to apply temperature increase (from 20 to 40 °C at 2 °C/min) and decrease (from 40 to 20 °C at 2°C/min) in a randomized order to the right eyelid, nose, right cheek, and forehead of 14 healthy young males. The facial SkBF was measured for 10 s using laser-speckle flowgraphy when temperatures of 20 °C, 30 °C, and 40 °C had been applied for 30 s in both trials.

RESULTS

The SkBF in the eyelid did not change significantly during any thermal stimulation, and the nasal SkBF did not decrease significantly during cold stimulation. The SkBFs in the cheek and forehead increased significantly with the applied temperature.

CONCLUSIONS

These findings indicate that a large regional variation exists in facial skin blood flow response to local heating or cooling and that the regional variation did not correspond to the unique SkBF responses in the previous studies.

Activity of frontal pole cortex reflecting hedonic tone of food and drink: fNIRS study in humans

Cognitive and hedonic aspects of taste have been studied using different neuroimaging techniques in humans. However, the methods used are unsuitable for easy monitoring of hedonics induced by intake of foods and beverages. Here we have tried to monitor changes in oxygenated hemoglobin (oxyHb) levels in the anterior prefrontal cortex (aPFC, frontopolar cortex, Brodmann area 10) in response to intake of hedonically different edibles in healthy adults. When subjects tasted sweet and bitter solutions freely without any particular instruction, cortical activation varied greatly among subjects and between the two stimuli, and no consistent results were obtained. Subjects then ate or drank preferred (hedonically positive) and disliked (hedonically negative) edibles. Although these stimuli differed among subjects, hedonically positive stimuli decreased oxyHb, whereas hedonically negative stimuli increased oxyHb, particularly in the ventral aPFC. When subjects tasted 4 kinds of jellies with different flavors and evaluated the degree of pleasantness, oxyHb level in the ventral region correlated negatively with pleasantness score. These results revealed that pleasant and unpleasant edibles tended to elicit decreased and increased oxyHb levels, respectively, within the ventral aPFC, suggesting that monitoring of oxyHb in this region may prove useful for objective evaluation of pleasantness of food and drink.

Transdermal optical imaging revealed different spatiotemporal patterns of facial cardiovascular activities

Human cardiovascular activities are important indicators of a variety of physiological and psychological activities in human neuroscience research. The present proof-of-concept study aimed to reveal the spatiotemporal patterns of cardiovascular activities from the dynamic changes in hemoglobin concentrations in the face. We first recorded the dynamics of facial transdermal blood flow using a digital video camera and the Electrocardiography (ECG) signals using an ECG system simultaneously. Then we decomposed the video imaging data extracted from different sub-regions of a face into independent components using group independent component analysis (group ICA). Finally, the ICA components that included cardiovascular activities were identified by correlating their magnitude spectrum to those obtained from the ECG. We found that cardiovascular activities were associated with five independent components reflecting different spatiotemporal dynamics of facial blood flow changes. The strongest strengths of these ICA components were observed in the bilateral forehead, the left chin, and the left cheek, respectively. Our findings suggest that the cardiovascular activities presented different dynamic properties within different facial sub-regions, respectively. More broadly, the present findings point to the potential of the transdermal optical imaging technology as a new neuroscience methodology to study human physiology and psychology, noninvasively and remotely in a contactless manner.

The interactions between different tastes on initiation of reflex swallow elicited by electrical stimulation in humans

The act of eating is a source of pleasure for people and is a major factor in maintaining a good quality of life. Several types of products for dysphagia patients are available to decrease aspiration of food that often accompanies daily food intake. The final goal of these products is to improve the ease of forming a food bolus and/or the safety of the swallowing process; however, tastes of products are not a major concern with initiation of swallowing. In the present study, we investigated the effect of bitter taste stimuli (quinine) and the combination of quinine and umami (monosodium glutamate: MSG) applied to the oropharynx on reflex swallows evoked by electrical stimulation to the oropharyngeal mucosa. Each of the distilled water (DW), quinine and quinine-MSG mixture solution (volume of each solutions, 100 µl) was applied 1 s prior to electrical stimulation. No swallow was evoked when each of the solutions was applied without electrical stimulation. The application of DW and lower concentration of quinine (<100 µM) did not affect the latency of reflex swallow, but 100 µM quinine application increased the latency of the reflex swallow. In addition, application of quinine-MSG mixture solution counteracted the increase in latency induced by quinine application alone. These findings suggest that MSG enhances the initiation of swallowing along with its well-known increase in appetite stimulation. Adding MSG might be effective when creating food to promote swallowing.

A novel objective sour taste evaluation method based on near-infrared spectroscopy

One of the most important themes in the development of foods and drinks is the accurate evaluation of taste properties. In general, a sensory evaluation system is frequently used for evaluating food and drink. This method, which is dependent on human senses, is highly sensitive but is influenced by the eating experience and food palatability of individuals, leading to subjective results. Therefore, a more effective method for objectively estimating taste properties is required. Here we show that salivary hemodynamic signals, as measured by near-infrared spectroscopy, are a useful objective indicator for evaluating sour taste stimulus. In addition, the hemodynamic responses of the parotid gland are closely correlated to the salivary secretion volume of the parotid gland in response to basic taste stimuli and respond to stimuli independently of the hedonic aspect. Moreover, we examined the hemodynamic responses to complex taste stimuli in food-based solutions and demonstrated for the first time that the complicated phenomenon of the "masking effect," which decreases taste intensity despite the additional taste components, can be successfully detected by near-infrared spectroscopy. In summary, this study is the first to demonstrate near-infrared spectroscopy as a novel tool for objectively evaluating complex sour taste properties in foods and drinks.

Palatability of tastes is associated with facial circulatory responses

To examine whether various types of taste stimuli in the oral cavity elicit unique changes in facial skin blood flow (SkBF) according to the palatability perceived by an individual, the facial SkBF was observed by laser speckle flowgraphy in 15 healthy subjects (11 males and 4 females) before and during the ingestion of bitter tea, chilli sauce, coffee, orange juice, soup, and a water control. The heart rate, mean arterial pressure (MAP), and SkBF in the index finger were recorded continuously. Subjects reported their subjective palatability and taste intensity scores after each stimulus. The vascular conductance indexes (CIs) in the face and finger were calculated as ratios of SkBF to MAP. CI in the eyelid increased significantly in response to chilli sauce, orange juice, and soup, whereas CIs in the forehead, nose, and cheek decreased in response to bitter tea. There was a significant correlation between the palatability scores and CI values in the eyelid when changes induced by chilli sauce were excluded. These results suggest that the facial circulatory response reflects the degree of palatability of a foodstuff.

Effect of a bitter bolus on oral, pharyngeal and esophageal transit of healthy subjects

CONTEXT

During swallowing, boluses stimulate sensory receptors of the oral, pharyngeal, laryngeal, and esophageal regions. Sweet and tasteless foods are more acceptable for swallowing than bitter foods. A bitter bolus is unpleasant for most subjects. Our hypothesis was that the ingestion of a bitter bolus might alter the oral behavior, pharyngeal and esophageal transit when compared to a sweet bolus.

OBJECTIVE

To evaluate whether the bitter taste of a liquid bolus causes alteration on oral, pharyngeal and/or esophageal transit in normal subjects in comparison with sweet bolus.'

METHOD

Scintigraphic evaluation of oral, pharyngeal and esophageal transit was performed in 43 asymptomatic subjects, 22 women and 21 men, ages 23-71 years, without problems with the ingestion of liquid and solid foods, and without digestive, cardiac or neurologic diseases. Each subject swallowed in random sequence and at room temperature 5 mL of a liquid bolus with bitter taste, prepared with 50 mL of water with 2 g of leaves of Peumus boldus, heated until boiling (boldus tea), and 5 mL of a liquid bolus with sweet taste, prepared with 50 mL of water with 3 g of sucrose, both labeled with 37 MBq of technetium phytate (Tc99m).

RESULTS

There was no difference between the bitter bolus and the sweet bolus in mouth, pharynx and esophageal transit and clearance duration and in the amount of residues.

CONCLUSION

A bitter bolus, considered an unpleasant bolus, does not alter the duration of oral, pharyngeal and esophageal phases of swallowing, when compared with a sweet bolus, considered a pleasant bolus.

Facial skin blood flow responses to irritant stimuli in the oral cavity

To investigate whether capsaicin and menthol stimuli elicit characteristic responses in facial skin blood flow (SkBF), we observed the facial SkBF response to low and high concentrations of capsaicin and menthol stimuli of 1-ml solution applied to the oral cavity for 20s in 17 healthy subjects. High concentration of capsaicin significantly increased the SkBF in all of the facial areas monitored. High concentration of menthol stimulus significantly decreased SkBF in the nose and increased that in the eyelid, and upper and lower lips. These results demonstrated that capsaicin and menthol stimuli in the oral cavity elicit characteristic responses in facial SkBF.

Regional differences in facial skin blood flow responses to the cold pressor and static handgrip tests

We have previously reported the unique regional responses of facial skin blood flow (SkBF) to oral application of the basic tastes without simultaneous systemic circulatory changes. In the present study, we determined whether a systemic circulatory challenge due to sympathetic activation induces regional differences in facial SkBF by observing the responses in facial SkBF and blood pressure to a 2-min cold pressor test (CPT) and static handgrip exercise (HG) by right hand in 20 healthy subjects. The CPT significantly increased SkBF in the forehead, eyelid, cheek, upper lip and lower lip by 6 ± 2 to 8 ± 2 % (mean ± SEM) as compared to resting baseline, with a significant simultaneous increase (13 ± 2 %) in mean arterial pressure (MAP), whereas it significantly decreased the SkBF in the nose by 5 ± 2 %. The HG significantly increased SkBF in the forehead, cheek and lower lip by 6 ± 3 to 10 ± 3 %, with a significant simultaneous increase in MAP (13 ± 2 %), while it induced no significant change in the other regions. Increases in SkBF were greater in the right than left cheek during CPT. These results demonstrate that a systemic circulatory challenge via sympathetic activation elicits regional differences in the facial SkBF response.