Multisensory flavor perception.

The perception of flavor is perhaps the most multisensory of our everyday experiences. The latest research by psychologists and cognitive neuroscientists increasingly reveals the complex multisensory interactions that give rise to the flavor experiences we all know and love, demonstrating how they rely on the integration of cues from all of the human senses. This Perspective explores the contributions of distinct senses to our perception of food and the growing realization that the same rules of multisensory integration that have been thoroughly explored in interactions between audition, vision, and touch may also explain the combination of the (admittedly harder to study) flavor senses. Academic advances are now spilling out into the real world, with chefs and food industry increasingly taking the latest scientific findings on board in their food design.

Motion perception in touch: resolving contradictory findings by varying probabilities of different trial types.

Representational momentum describes the typical overestimation of the final location of a moving stimulus in the direction of stimulus motion. While systematically observed in different sensory modalities, especially vision and audition, in touch, empirical findings indicate a mixed pattern of results, with some published studies suggesting the existence of the phenomenon, while others do not. In the present study, one possible moderating variable, the relative probabilities of different trial types, was explored in an attempt to resolve the seemingly contradictory findings in the literature. In some studies, only consistently moving target stimuli were presented and no representational momentum was observed, while other studies have included inconsistently moving target stimuli in the same experimental block, and observed representational momentum. Therefore, the present study was designed to systematically compare the localization of consistent target motion stimuli across two experimental blocks, for which either only consistent motion trials were presented, or else mixed with inconsistent target motion trials. The results indicate a strong influence of variations in the probability of different trial types on the occurrence of representational momentum. That is, representational momentum only occurred when both trial types (inconsistent and consistent target motion) were presented within one experimental block. The results are discussed in light of recent theoretical advancements in the literature, namely the speed prior account of motion perception.

Multisensory contributions to skin-cosmetic product interactions.

The human face is one of the most salient regions of the body surface. Ratings of facial attractiveness, as well as judgements of a person's age, are influenced by the appearance of facial skin (not to mention the presence/absence of wrinkles). Unsurprisingly, many consumers spend huge amounts of money on trying to protect, maintain, and/or enhance their facial appearance. As highlighted by the evidence presented in this narrative review, both the skin and the cosmetic products that many consumers use are fundamentally multisensory in nature. The complex interaction between the particular skin site stimulated and the multisensory attributes of the product (e.g., when it is applied) can exert a number of effects on an individual's mood, their emotions, as well as on their self-perception (and self-confidence), over-and-above any functional effects that the cream or lotion may have on the skin itself. In this narrative historical review, the literature on the multisensory perception of facial skin is summarized and critically evaluated. Multisensory interactions taking place between the cosmetic product, its packaging, as well as its use/application at the sensory, cognitive, and emotional levels are all discussed.

Le visage humain est l'une des régions les plus visibles de la surface du corps. L'apparence de la peau du visage (sans parler de la présence ou de l'absence de rides) influe sur l'évaluation de l'attrait du visage et sur le jugement de l'âge d'une personne. Il n'est donc pas surprenant que de nombreux consommateurs dépensent des sommes considérables pour essayer de protéger, d'entretenir et/ou d'améliorer l'apparence de leur visage. Comme le montrent les données présentées dans cette synthèse, la peau et les produits cosmétiques utilisés par de nombreux consommateurs sont fondamentalement multisensoriels par nature. L'interaction complexe entre le site cutané stimulé et les attributs multisensoriels du produit (par exemple, lorsqu'il est appliqué) peut exercer un certain nombre d'effets sur l'humeur et les émotions d'un individu, ainsi que sur la perception de soi (et la confiance en soi), au­delà de tout effet fonctionnel que la crème ou la lotion peut avoir sur la peau elle­même.

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.

Individual Differences in Chemosensory Perception Amongst Cancer Patients Undergoing Chemotherapy: A Narrative Review.

Chemotherapy is an aggressive form of treatment for cancer and its toxicity directly affects the eating behavior of many patients, usually by adversely affecting their sense of smell and/or taste. These sensory alterations often lead to serious nutritional deficiencies that can jeopardize the patient's recovery, and even continue to affect their lives once treatment has terminated. Importantly, however, not all patients suffer from such alterations to their chemical senses; and those who do, do not necessarily describe the side effects in quite the same way, nor suffer from them with equal intensity. The origin of these individual differences between cancer patients undergoing chemotherapy treatment has not, as yet, been studied in detail. This review is therefore designed to encourage future research that can help to address the perceptual/sensory problems (and the consequent malnutrition) identified amongst this group of patients in a more customized/personalized manner. In particular, by providing an overview of the possible causes of these large individual differences that have been reported in the literature. For this reason, in addition to the narrative bibliographic review, several possible strategies that could help to improve the chemosensory perception of food are proposed.

No self-advantage in recognizing photographs of one's own hand: experimental and meta-analytic evidence.

Visually recognising one's own body is important both for controlling movement and for one's sense of self. Twenty previous studies asked healthy adults to make rapid recognition judgements about photographs of their own and other peoples' hands. Some of these judgements involved explicit self-recognition: "Is this your hand or another person's?" while others assessed self-recognition implicitly, comparing performance for self and other hands in tasks unrelated to self-other discrimination (e.g., left-versus-right; match-to-sample). We report five experiments with three groups of participants performing left-versus-right (Experiment 1) and self-versus-other discrimination tasks (Experiments 2 to 5). No evidence was found for better performance with self than with other stimuli, but some evidence was found for a self-disadvantage in the explicit task. Manipulating stimulus duration as a proxy for task difficulty revealed strong response biases in the explicit self-recognition task. Rather than discriminating between self and other stimuli, participants seem to treat self-other discrimination tasks as self-detection tasks, raising their criterion and consistently responding 'not me' when the task is difficult. A meta-analysis of 21 studies revealed no overall self-advantage, and suggested a publication bias for reports showing self-advantages in implicit tasks. Although this may appear counter-intuitive, we suggest that there may be no self-advantage in hand recognition.

Top-down task-specific determinants of multisensory motor reaction time enhancements and sensory switch costs.

This study was designed to investigate the complex interplay between multisensory processing, top-down processes related to the task relevance of sensory signals, and sensory switching. Thirty-five adults completed either a speeded detection or a discrimination task using the same auditory and visual stimuli and experimental setup. The stimuli consisted of unisensory and multisensory presentations of the letters 'b' and 'd'. The multisensory stimuli were either congruent (e.g., the grapheme 'b' with the phoneme /b/) or incongruent (e.g., the grapheme 'b' with the phoneme /d/). In the detection task, the participants had to respond to all of the stimuli as rapidly as possible while, in the discrimination task, they only responded on those trials where one prespecified letter (either 'b' or 'd') was present. Incongruent multisensory stimuli resulted in faster responses as compared to unisensory stimuli in the detection task. In the discrimination task, only the dual-target congruent stimuli resulted in faster RTs, while the incongruent multisensory stimuli led to slower RTs than to unisensory stimuli; RTs were the slowest when the visual (rather than the auditory) signal was irrelevant, thus suggesting visual dominance. Switch costs were also observed when switching between unisensory target stimuli, while dual-target multisensory stimuli were less likely to be affected by sensory switching. Taken together, these findings suggest that multisensory motor enhancements and sensory switch costs are influenced by top-down modulations determined by task instructions, which can override the influence of prior learnt associations.

Responding to sounds from unseen locations: crossmodal attentional orienting in response to sounds presented from the rear.

To date, most of the research on spatial attention has focused on probing people's responses to stimuli presented in frontal space. That is, few researchers have attempted to assess what happens in the space that is currently unseen (essentially rear space). In a sense, then, 'out of sight' is, very much, 'out of mind'. In this review, we highlight what is presently known about the perception and processing of sensory stimuli (focusing on sounds) whose source is not currently visible. We briefly summarize known differences in the localizability of sounds presented from different locations in 3D space, and discuss the consequences for the crossmodal attentional and multisensory perceptual interactions taking place in various regions of space. The latest research now clearly shows that the kinds of crossmodal interactions that take place in rear space are very often different in kind from those that have been documented in frontal space. Developing a better understanding of how people respond to unseen sound sources in naturalistic environments by integrating findings emerging from multiple fields of research will likely lead to the design of better warning signals in the future. This review highlights the need for neuroscientists interested in spatial attention to spend more time researching what happens (in terms of the covert and overt crossmodal orienting of attention) in rear space.

The Mystery of "Metal Mouth" in Chemotherapy.

Of all the oral sensations that are experienced, "metallic" is one that is rarely reported in healthy participants. So why, then, do chemotherapy patients so frequently report that "metallic" sensations overpower and interfere with their enjoyment of food and drink? This side-effect of chemotherapy-often referred to (e.g., by patients) as "metal mouth"-can adversely affect their appetite, resulting in weight loss, which potentially endangers (or at the very least slows) their recovery. The etiology of "metal mouth" is poorly understood, and current management strategies are largely unevidenced. As a result, patients continue to suffer as a result of this poorly understood phenomenon. Here, we provide our perspective on the issue, outlining the evidence for a range of possible etiologies, and highlighting key research questions. We explore the evidence for "metallic" as a putative taste, and whether "metal mouth" might therefore be a form of phantageusia, perhaps similar to already-described "release-of-inhibition" phenomena. We comment on the possibility that "metal mouth" may simply be a direct effect of chemotherapy drugs. We present the novel theory that "metal mouth" may be linked to chemotherapy-induced sensitization of TRPV1. Finally, we discuss the evidence for retronasal olfaction of lipid oxidation products in the etiology of "metal mouth." This article seeks principally to guide much-needed future research which will hopefully one day provide a basis for the development of novel supportive therapies for future generations of patients undergoing chemotherapy.

Factors affecting flavor perception in space: Does the spacecraft environment influence food intake by astronauts?

The intention to send a crewed mission to Mars involves a huge amount of planning to ensure a safe and successful mission. Providing adequate amounts of food for the crew is a major task, but 20 years of feeding astronauts on the International Space Station (ISS) have resulted in a good knowledge base. A crucial observation from the ISS is that astronauts typically consume only 80% of their daily calorie requirements when in space. This is despite daily exercise regimes that keep energy usage at very similar levels to those found on Earth. This calorie deficit seems to have little effect on astronauts who spend up to 12 months on the ISS, but given that a mission to Mars would take 30 to 36 months to complete, there is concern that a calorie deficit over this period may lead to adverse effects in crew members. The key question is why astronauts undereat when they have a supply of food designed to fully deliver their nutritional needs. This review focuses on evidence from astronauts that foods taste different in space, compared to on Earth. The underlying hypothesis is that conditions in space may change the perceived flavor of the food, and this flavor change may, in turn, lead to underconsumption by astronauts. The key areas investigated in this review for their potential impact on food intake are the effects of food shelf life, physiological changes, noise, air and water quality on the perception of food flavor, as well as the link between food flavor and food intake.

The contradictory influence of velocity: representational momentum in the tactile modality.

Representational momentum (RM) is the term used to describe a systematic mislocalization of dynamic stimuli, a forward shift; that is, an overestimation of the location of a stimulus along its anticipated trajectory. In the present study, we investigate the effect of velocity on tactile RM, because two distinct and contrasting predictions can be made, based on different theoretical accounts. According to classical accounts of RM, based on numerous visual and auditory RM studies, an increase of the forward shift with increasing target velocity is predicted. In contrast, theoretical accounts explaining spatiotemporal tactile illusions such as the tau or cutaneous rabbit effect predict a decrease of the forward shift with increasing target velocity. In three experiments reported here, a tactile experimental setup modeled on existing RM setups was implemented. Participants indicated the last location of a sequence of three tactile stimuli, which either did or did not imply motion in a consistent direction toward the elbow/wrist. Velocity was manipulated by changing the interstimulus interval as well as the duration of the stimuli. The results reveal that increasing target velocity led to a decrease and even a reversal of the forward shift, resulting in a backward shift. This result is consistent with predictions based on the evidence from tactile spatiotemporal illusions. The theoretical implications of these results for RM are discussed. NEW & NOTEWORTHY This study tests two distinct predictions concerning the influence of velocity on the localization of dynamic tactile stimuli. We demonstrate for tactile stimuli that with increasing velocity, a misperception in the direction of anticipated motion (termed "representational momentum") turns into a misperception against the direction of motion. This result is in line with predictions based on tactile spatiotemporal illusions but challenges classical theoretical accounts of representational momentum based on evidence from vision and audition.

"What Smell?" Temporarily Loading Visual Attention Induces a Prolonged Loss of Olfactory Awareness.

The human sense of smell is highly sensitive, often conveying important biological signals. Yet anecdotal evidence suggests that we commonly fail to notice suprathreshold environmental olfactory stimuli. The determinants of olfactory awareness are, as yet, unknown. Here, we adapted the inattentional-blindness paradigm to test whether olfactory awareness is dependent on attention. Across three experiments, participants performed a visual search task with either a high or low perceptual load (a well-established attentional manipulation) while exposed to an ambient coffee aroma. Consistent with our hypothesis, results showed that task load modulated olfactory awareness: 42.5% fewer participants in the high- than in the low-load condition reported noticing the coffee aroma. Our final experiment demonstrates that because of unique characteristics of olfactory habituation, the consequences of inattentional anosmia can persist even once attention becomes available. These findings establish the phenomenon of inattentional anosmia and have applied implications for predicting when people may miss potentially important olfactory information.

On the Meaning(s) of Perceived Complexity in the Chemical Senses.

Complexity is a term that is often invoked by those writing appreciatively about the taste, aroma/bouquet, and/or flavor of food and drink. Typically, the term is used as though everyone knows what is being talked about. Rarely is any explanation given, and the discussion soon moves on to other topics. However, oftentimes it is not at all clear what, exactly, is being referred to. A number of possibilities are outlined here, including physical complexity at the level of individual molecules, at the level of combinations of molecules giving rise to a specific flavor profile (e.g., as in a glass of quality wine or a cup of specialty coffee), at the level of combinations of distinct ingredients/elements (e.g., as when composing a particularly intricate dish in a high-end restaurant, say, or when pairing food with wine), and/or the number of stimuli/steps involved in the process of creation. Of course, people might also be referring to some aspect of their perceptual experience, and one of the intriguing questions in this space concerns the nature of the relationship(s) between these different ways of conceptualizing complexity in the chemical senses. However, given that physical/chemical and perceived complexity so often diverge, we argue that it is the latter notion, or rather inferred complexity, that is the most relevant when it comes to the chemical senses. Finally, we look at the role of expertise and review the evidence suggesting that inferred complexity can emerge either from a unitary taste experience that is judged to be complex, or from a tasting experience having multiple individuable elements.

Multisensory enhancement elicited by unconscious visual stimuli.

The merging of information from different senses (i.e., multisensory integration) can facilitate information processing. Processing enhancements have been observed with signals that are irrelevant to the task at hand, and with cues that are non-predictive. Such findings are consistent with the notion that multiple sensory signals are sometimes integrated automatically. Multisensory enhancement has even been reported with stimuli that have been presented subliminally, though only with meaningful multisensory relations that have already been learned. The question of whether there exist cases where multisensory effects occur without either learning or awareness has, though, not been clearly established in the literature to date. Here, we present a case study of a patient with Posterior Cortical Atrophy, who was unable to consciously perceive visual stimuli with our task parameters, yet who nevertheless still exhibited signs of multisensory enhancement even with unlearned relations between audiovisual stimuli. In a simple speeded detection task, both response speed, and the variability of reaction times, decreased in a similar manner to controls for multisensory stimuli. These results are consistent with the view that the conscious perception of stimuli and prior learning are not always a prerequisite for multisensory integration to enhance human performance.

Sensitivity to auditory-tactile colocation in early infancy.

An ability to detect the common location of multisensory stimulation is essential for us to perceive a coherent environment, to represent the interface between the body and the external world, and to act on sensory information. Regarding the tactile environment "at hand", we need to represent somatosensory stimuli impinging on the skin surface in the same spatial reference frame as distal stimuli, such as those transduced by vision and audition. Across two experiments we investigated whether 6- (n = 14; Experiment 1) and 4-month-old (n = 14; Experiment 2) infants were sensitive to the colocation of tactile and auditory signals delivered to the hands. We recorded infants' visual preferences for spatially congruent and incongruent auditory-tactile events delivered to their hands. At 6 months, infants looked longer toward incongruent stimuli, whilst at 4 months infants looked longer toward congruent stimuli. Thus, even from 4 months of age, infants are sensitive to the colocation of simultaneously presented auditory and tactile stimuli. We conclude that 4- and 6-month-old infants can represent auditory and tactile stimuli in a common spatial frame of reference. We explain the age-wise shift in infants' preferences from congruent to incongruent in terms of an increased preference for novel crossmodal spatial relations based on the accumulation of experience. A comparison of looking preferences across the congruent and incongruent conditions with a unisensory control condition indicates that the ability to perceive auditory-tactile colocation is based on a crossmodal rather than a supramodal spatial code by 6 months of age at least.

Space-based bias of covert visual attention in complex regional pain syndrome.

See Legrain (doi:10.1093/awx188) for a scientific commentary on this article. Some patients with complex regional pain syndrome report that movements of the affected limb are slow, more effortful, and lack automaticity. These symptoms have been likened to the syndrome that sometimes follows brain injury called hemispatial neglect, in which patients exhibit attentional impairments and problems with movements affecting the contralesional side of the body and space. Psychophysical testing of patients with complex regional pain syndrome has found evidence for spatial biases when judging visual targets distanced at 2 m, but not in directions that indicate reduced attention to the affected side. In contrast, when judging visual or tactile stimuli presented on their own body surface, or pictures of hands and feet within arm's reach, patients with complex regional pain syndrome exhibited a bias away from the affected side. What is not yet known is whether patients with complex regional pain syndrome only have biased attention for bodily-specific information in the space within arm's reach, or whether they also show a bias for information that is not associated with the body, suggesting a more generalized attention deficit. Using a temporal order judgement task, we found that patients with complex regional pain syndrome processed visual stimuli more slowly on the affected side (relative to the unaffected side) when the lights were projected onto a blank surface (i.e. when no bodily information was visible), and when the lights were projected onto the dorsal surfaces of their uncrossed hands. However, with the arms crossed (such that the left and right lights projected onto the right and left hands, respectively), patients' responses were no different than controls. These results provide the first demonstration of a generalized attention bias away from the affected side of space in complex regional pain syndrome patients that is not specifically related to bodily information. They also suggest a separate and additional bias of visual attention away from the affected hand. The strength of attention bias was predicted by scores on a self-report measure of body perception distortion; but not by pain intensity, time since diagnosis, or affected body side (left or right). At an individual level, those patients whose upper limbs were most affected had a higher incidence of inattention than those whose lower limbs were most affected. However, at a group level, affected limb (upper or lower) did not predict bias magnitude; nor did three measures designed to assess possible asymmetries in the distribution of movements across space. It is concluded that inattention in near space in complex regional pain syndrome may arise in parallel with a distorted perception of the body.10.1093/brain/awx152_video1awx152media15495542665001.

Developmental changes in the perception of visuotactile simultaneity.

A simultaneity judgment (SJ) task was used to measure the developmental trajectory of visuotactile simultaneity perception in children (aged 7, 9, 11, and 13 years) and adults. Participants were presented with a visual flash in the center of a computer monitor and a tap on their right index finger (located 20° below the flash) with 13 possible stimulus onset asynchronies (SOAs). Participants reported whether the flash and tap were presented at the same time. Compared with the adult group, children aged 7 and 9 years made more simultaneous responses when the tap led by more than 300 ms and when the flash led by more than 200 ms, whereas they made fewer simultaneous responses at the 0 ms SOA. Model fitting demonstrated that the window of visuotactile simultaneity became narrower with development and reached adult-like levels between 9 and 11 years of age. Response errors decreased continuously until 11 years of age. The point of subjective simultaneity (PSS) was located on the tactile-leading side in all participants tested, indicating that 7-year olds (the youngest age tested) are adult-like on this measure. In summary, the perception of visuotactile simultaneity is not fully mature until 11 years of age. The protracted development of visuotactile simultaneity perception may be related to the need for crossmodal recalibration as the body grows and to the developmental improvements in the ability to optimally integrate visual and tactile signals.

Does the visual composition of a dish influence the perception of portion size and hedonic preference?

We report two experiments designed to assess how the plating (i.e., visual composition) of a dish influences people's hedonic preferences and their perception of portion size. In Experiment 1 (conducted online; N = 122), we examined whether varying the orientation of the food on the plate (either vertically stacked or horizontally arrayed) would affect people's ratings of liking (of the visual arrangement), willingness-to-pay for the dish, artistic value (how artistic the dish looks), and perceived portion size. Experiment 2 (N = 124) extended this research to a naturalistic dining context, demonstrating the influence of both plating arrangement (horizontal vs. vertical) and centrality (centred vs. offset plating) on the same ratings. In both experiments, the plate of food was rated as constituting a larger portion when the elements were arrayed-horizontally rather than stacked vertically. Additionally, the centrally-plated dessert was rated as a larger portion than the offset version of exactly the same dish. The food was also liked more and the participants/diners were willing to pay more for it when horizontally and/or centrally arranged. These results provide important guidelines for enhancing the visual arrangement of a dish, in order to increase enjoyment, and possibly also nudge consumers toward better food choices.

"A sweet smile": the modulatory role of emotion in how extrinsic factors influence taste evaluation.

It has recently been demonstrated that the reported tastes/flavours of food/beverages can be modulated by means of external visual and auditory stimuli such as typeface, shapes, and music. The present study was designed to assess the role of the emotional valence of the product-extrinsic stimuli in such crossmodal modulations of taste. Participants evaluated samples of mixed fruit juice whilst simultaneously being presented with auditory or visual stimuli having either positive or negative valence. The soundtracks had either been harmonised with consonant (positive valence) or dissonant (negative valence) musical intervals. The visual stimuli consisted of images of emotional faces from the International Affective Picture System (IAPS) with valence ratings matched to the soundtracks. Each juice sample was rated on two computer-based scales: One anchored with the words sour and sweet, while the other scale required hedonic ratings. Those participants who tasted the juice sample while presented with the positively-valenced stimuli rated the juice as tasting sweeter compared to negatively-valenced stimuli, regardless of whether the stimuli were visual or auditory. These results suggest that the emotional valence of food-extrinsic stimuli can play a role in shaping food flavour evaluation and liking.

A New Kind of Spatial Inattention Associated With Chronic Limb Pain?

Pathological limb pain patients show decreased attention to some stimuli on the painful limb and increased attention to others, a paradox that has dogged the field for over a decade. We hypothesized that pathological pain involves a spatial inattention confined to bodily representations. Patients showed inattention to the painful side for visual processing of body parts but not letters, tactile processing but not auditory, and body-part bisection tasks but not line bisection tasks. We propose the new term "somatospatial inattention" to describe bodily-specific spatial inattention associated with pathological limb pain.