Science and society: Challenges for the sensory sciences from the food and wine industries

© 2003 Nature Publishing Group

PERSPECTIVES

of the neurophysiological and behaviouralresponses.

Under controlled conditions, humans canprovide direct measures of the intrinsic sensoryproperties of stimuli, such as the smell, tasteand feel of food or wine. Perception of theseproperties is altered by physiological factorssuch as nutritional deficiency, thirst, satiety,hormonal status, disease and age, as well as bythe testing conditions, level of training andinformation available to the subjects.

In addition to a product’s intrinsic sensoryproperties, a consumer’s decision to purchase aproduct is influenced by extrinsic propertiessuch as the price, appearance of the label,brand or colour of the product. The purchasedecision and subsequent determination ofoverall acceptability are also affected by a con-sumer’s expectation of the product, which isbased on factors such as previous experience,expert recommendation and brand familiarity.The circumstances surrounding consumptionof the product exert another layer of influenceon the consumer’s processing, perception andacceptance. Drinking an inexpensive winebeside the Loire River is usually far morepleasurable than consuming the same wine at home.

To make a product that is liked and pur-chased, the food, wine, flavour and fragranceindustries need to know the effect of composi-tion on a product’s sensory properties. Theyneed to understand how these sensations areperceived, how non-sensory factors modify theperception of sensory stimuli, and how overallpreference and purchase decisions are made.

What can sensory neuroscience do forproducers of commodities, such as wine, foodor fragrance, for which sensory properties areimportant? Almost anything that can belearned about factors that influence perceptioncan be used by these industries to increasetheir market share.

Human sensory scienceNarrowly defined, psychophysics is the studyof relationships between a stimulus and theresponse that it evokes. Different approachesare used for analytical (discrimination ordescriptive tests) and affective (hedonic)evaluations1, and the techniques used caninclude difference testing, sorting and rankingor rating procedures. Analytical evaluationinvolves discriminating between stimuli, ordescribing the nature and size of the differ-ences between stimuli. All external sources ofinformation, except those being tested, areexcluded to remove any bias or expectationthat might influence perception. For example,stimulus appearance has a large effect on theperception of taste and smell. Experiencedwine judges rated white wines that werecoloured to resemble rosé wines as beingsweeter than the uncoloured white wine2.By contrast, the sweetness ratings of naivesubjects were not influenced by wine colour.

In analytical tests, subjects are treated asanalytical instruments, so extensive training isconducted to minimize experimental noiseand increase sensitivity. For descriptive tests,subjects are trained to perform scaling tasks,rating intensity either at a single point or continuously over time. Training is also usedfor aligning concepts to increase consistencyof responses, for example, to discriminatesourness from bitterness or peach aromafrom citrus aroma.

In contrast to analytical tests, hedonic eval-uations of preference require that subjects beconsumers of the products being tested.Testingis sometimes done blind,but more valid resultscan be determined when the biases and factorsthat affect the consumer during purchase(such as price or label design) are included3.

When scientists describe their research tonon-scientists, the most common questionis ‘what is the practical value of your work?’The methods that are used to measureresponses to sensory stimuli in humansensory science and neuroscience researchhave great potential value to the food andwine industries, as well as promising toadvance our understanding of themechanisms by which sensations areperceived and processed.

Sensory and perceptual measures of taste,smell and touch are routinely obtained fromanimals. However, such measures reflect theintensity of the stimulus as well as its quality(for example, sucrose versus acid), similarityto other stimuli and/or preference, and cannotprovide the crucial details regarding the sens-ation that is actually perceived. Without thehuman description of such sensations, dataobtained from these types of experiments can-not be interpreted in terms of human sensoryexperience. For instance, noxious stimuli willreadily evoke cellular nociceptive responsesand nocifensive behaviours in animals,but we cannot know whether the animals actually experience ‘pain’ because they cannot describe their experiences. On the other hand, humans, who can verbally report anddescribe responses to stimuli, cannot usuallybe examined using the invasive neurosciencemethods used in animal studies. Therefore,responses obtained from animals need to becorrelated with human studies of similarstimuli to interpret the nature and significance

NATURE REVIEWS | NEUROSCIENCE VOLUME 4 | JULY 2003 | 599

Challenges for the sensory sciencesfrom the food and wine industries

Christopher T. Simons and Ann C. Noble

S C I E N C E A N D S O C I E T Y


600 | JULY 2003 | VOLUME 4 www.nature.com/reviews/neuro

P E R S P E C T I V E S

identified by external preference mapping8, inwhich the average preference ratings for eachcluster were regressed to a multi-dimensionalrepresentation of the wines’ flavour. This con-figuration of the wines is derived by principalcomponent analysis of descriptive analysisdata. In FIG. 2b, the loadings for the sensoryattributes and the wine factor scores for thefirst two principal components are plottedwith the consumer cluster preference scores.Clusters 1, 2 and 3 were fit by vector models,and the direction of the arrow indicates theirdirection of increased preference. Cluster 1disliked wines (D, S, F) that were high in floralaroma and low in butter aroma and caramelflavour. Cluster 2 preferred wines that werehigh in astringency and oak-associated notesand low in fruity character (wines A, J, B, G).Cluster 3 preferred wines such as D, S and Fthat were high in floral and fruity notes, andlow in oak-related ones.

Whereas the intrinsic sensory properties offoods and wines are important in consumeracceptance, at the time of purchase, the consumer can only evaluate extrinsic factorssuch as packaging, brand, price and labelappearance. Therefore, purchase decisions aremade on the appeal of these aspects alone or in

Affective sensory tests. Descriptive analysiscannot predict consumer preference. To deter-mine which products are preferred, targetconsumers need to be recruited for acceptancetests. In central location testing, consumersrate preferences for coded samples in a testingfacility. As a consequence, their responses arealmost exclusively based on the sensory properties of the stimulus. For example, 125consumers rated preference for the tenChardonnay wines described earlier undertwo conditions: first with the wines coded, andthen with the wines identified7. In both condi-tions, the judges could see, taste and smell thewines. The internal preference map8, con-structed by principal component analysis ofblind preference ratings, is shown in FIG. 2a,where each numbered square represents aconsumer. The scatter of the consumers showsgreat variation in preference. If the consumershad similar preferences, their responses wouldbe highly correlated and the loadings for theconsumers would be clustered in a small area.

Despite the apparent lack of agreementamong the consumers, cluster analysis of thesame blind preference ratings revealed fiveconsumer segments. The sensory propertiesof wines preferred by each segment were

Analytical sensory tests. The first type ofanalytical tests, difference tests, are used tomeasure small variations in subject sensitivitydue to treatment or subject condition. Thesetests also allow researchers to study the cogni-tive strategies that are used by subjects to detectdifferences4. Generally, tests to detect uni-dimensional sensory differences are relativelysimple (for example, ‘which sample is moresalty?’). Despite their simplicity, informationfrom these experiments has proven useful insensory neuroscience. For example, in rats,dorzolamide (a carbonic anhydrase anta-gonist) blocks the neural activity that is elicitedby carbonated water, indicating that this sensa-tion is of a chemogenic rather than a mech-anical (bursting bubbles) origin. To correlatethese findings with human sensation, dorzo-lamide was applied unilaterally to the tonguesof volunteers5. Subjects consistently chose theuntreated side as having a stronger ‘tingling’sensation. So, both human and animal datacorroborate the chemogenic hypothesis for thesensation that is elicited by carbonated water.

The second type of analytical test isdescriptive. In basic research, relationshipsbetween dose and response are determined fora specific sensation. However, in addition tointensity, the nature, composition and methodof stimulus presentation also determine itsspecific sensory characteristics and temporalproperties. For example, fructose is sweeterthan sucrose on an equal weight basis, andnon-carbohydrate sweeteners such as aspar-tame are even more potent. In addition, therate of sweetness onset (increase) and decay(decrease) varies between non-carbohydratesweeteners and sugars. Monitoring sweetnessintensity over time using time–intensitymethodology provides sweetness curves thathave been used in product formulation as wellas in modelling taste perception6.

The response to complex stimuli such asfood or wine is multidimensional. Therefore,scaling of many attributes is required to measure and describe differences amongproducts and to profile their flavours. Indescriptive analysis, the intensity of terms thathave been selected to characterize and dis-criminate among stimuli or products is ratedunder controlled conditions by trainedjudges. Descriptive analysis of ten commercialChardonnay wines revealed that the primaryvariation in flavour was a contrast betweenwines that were high in the intensity of oak,butter and vanilla notes and low in fruity and floral aromas, and wines that were high in fruity/floral notes and low in the oak-associated terms7. FIGURE 1 shows profiles ofthree ‘oaky’ wines (E, G and J) and two ‘fruity’wines (C and D).

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Figure 1 | Evaluation of aroma, taste and ‘flavour by mouth’. Mean intensities of aroma, taste andflavour-by-mouth attributes for five wines (C, D, E, G and J) rated on a nine-point category scale, where 1is low and 9 is high. Origin = 1; perimeter = 7. Means for a wine are connected to provide a profile. Datarepresent three repetitions for thirteen subjects7.



tion that is associated with fat ingestion13,food processing companies could develop fat replacers with sensory characteristics that more accurately reflect the sensationsperceived when ingesting whole-fat foods.

Combining molecular approaches withpowerful physiological and behavioural tools,

combination with previous knowledge aboutintrinsic factors. As a consequence, for con-sumer studies to provide valid results aboutpurchasing behaviour, the evaluations mustconsider factors other than the intrinsic sen-sory properties. In Yegge’s study7, one wine wasevaluated in duplicate under both conditions,but in the informed condition, the duplicatewines were identified by two different labels.More than 50 of the 125 consumers rated thiswine much more highly when it was identifiedas brand A rather than as brand B. In real pur-chasing situations, as these results illustrate,‘non-sensory’ attributes such as brand areweighted differently by different individuals.

Sensory neuroscienceThe techniques used in sensory science mea-sure the sensations that are experienced whenfoods or beverages are consumed.Although allof the senses contribute to the overall percep-tion of a given food or beverage, gustatory,olfactory and oral somatosensory stimuli havethe largest impact. The verbal response ofa subject in a sensory experiment reflects the unique perceptual construct that arises from stimuli that are processed more-or-lessseparately in the gustatory, olfactory andsomatosensory pathways. Specific patterns ofinformation from these three channels (as wellas visual input) converge at higher cortical centres9 to generate the unique flavour profileof a product.

The neural activity in each of the threesensory systems encodes important informa-tion about the physical characteristics of astimulus. Moreover, the encoded informationis continuously processed as it is conveyed to higher levels of the neuraxis, to providemeaning and relevancy to the information.

At the molecular level, technologicaladvances have allowed investigators to beginto identify the receptor proteins that generatethe stimulus-induced signals that are respon-sible for sensations of smell, taste or oral irri-tation. The identification of a large family of G-protein-coupled receptors10 that areexpressed by olfactory receptor cells has laid the foundation for further experimentsdetailing the structure–function relationshipsof the receptor– ligand complexes. Similarly,investigators in the fields of gustation andsomatosensation have identified receptorsthat transduce specific taste sensations11 orirritant sensations associated with spicyfoods12. The practical implications of thesetypes of study are vast. As further informationis accumulated, consumer industries mightexploit these findings to produce agonist andantagonist agents to elicit or block specificsensations. For instance, coating cruciferous

vegetables with an antagonist that is specificto bitter receptors might ameliorate the bitteraftertaste that is associated with many ofthese products, and which is often perceivedas undesirable. Similarly, by recognizing thatboth taste and somatosensory transductionmechanisms might underlie the oral sensa-


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Figure 2 | Preference mapping for wines. a | Internal preference map for (blind) preference ratings of 10wines by 125 consumers. Axes 1 and 2 account for 34% of the preference variation among consumers.The loadings for each consumer are shown by squares. The absence of clustering of consumers indicatestheir widely varying preferences7. b | External preference mapping of (blind) preference ratings of fiveconsumer segments. Axes 1 and 2 account for 85% of the variation among consumers. Factor scores forwines are indicated by letters; the loadings for the sensory terms are noted by blue circles. The averagecluster preference is denoted by a triangle and number. Clusters 1, 2 and 3 were fit by vector models: thearrow shows the direction of increasing preference for each segment. Cluster 1 disliked wines (D,S,F) thatwas high in floral aroma and lower in butter aroma and caramel flavour. Cluster 2 preferred wines that werehigh in astringency and oak-associated aroma notes, and low in peach and citrus aromas, apple flavour-by-mouth characters (A, B, G, J). Cluster 3, conversely, preferred wines D, S and F, which were high infloral and fruity notes, and low in oak-related ones7.




Satiety. Satiety has an important impact onthe acceptance and intake of food. Therefore,understanding its mechanism has immediatepragmatic value to the food industry.Important progress has been made in identify-ing the numerous elements that mediate satiety, including gastric stretch receptors,thermogenesis and various endocrinefactors32. Moreover, neurophysiological andfMRI studies have revealed that after satiation,tastant- and odorant-evoked responses aresuppressed in brain areas that are thought tobe associated with motivation and reinforce-ment16,33. Nevertheless, the mechanism bywhich many endocrine factors, especially satiety peptides, interface with neural substrates to influence the valence and moti-vational factors of foods is not clear.Knowledge of these vital details might givefood companies the necessary insight, forexample, to develop diet foods that have morecomprehensive satiating properties.

PROP status and perception. In taste tests,individuals vary widely in their sensitivity to 6-n-propyl thiouracil (PROP), as reflected inPROP threshold levels and reported intensityratings of suprathreshold PROP concentra-tions. The variation in PROP responses is presumed to have a genetic basis that explainsthe classification of individuals into threegroups: those that are insensitive (non-tasters), moderately sensitive (tasters) andacutely sensitive (supertasters)34. Physiologicaldissimilarities might partly explain the percep-tual differences noted among these groups.Although there is significant overlap, super-tasters are often reported to have a higher density of fungiform papillae and a largernumber of taste pores per papillae comparedwith tasters, who in turn have higher papillaedensities and taste-pore counts than non-tasters34. Despite these physiological differ-ences, the relationship of PROP sensitivity tothe perception of other tastants or oral irritants is not clear35, and the idea that PROPsensitivity influences preference for bitterproducts such as tea, coffee or grapefruit iscontroversial. Although the use of differentprotocols and scaling methods might explainsome of the inconsistencies in results36, it ispossible that brain imaging of humans that areclassified according to taster status could produce an unequivocal answer. Alternatively,recent studies have found that PROP avoid-ance in mice might be a polygenic trait37,providing the potential opportunity todevelop an animal model with differential sen-sitivity to PROP. Correlating behaviouralresponses with electrophysiological recordingsfrom various locations along the taste and

confirm or refute hypotheses derived fromanimal experiments. Carboxcylic acids ofvarying chain length that evoke identicalresponses in the rabbit olfactory bulb cannotbe discriminated by humans24,25. Similarly,lingual application of amiloride, an inhibitorof sodium transport, reduces both the perceived intensity of NaCl solutions inhumans26 and the firing rate that is evoked byNaCl in rat taste nerves27. Psychophysicalexperiments also provide crucial details aboutperceptual experience that are unavailableusing molecular and cellular approaches. Inthis regard, psychophysics is the only way tolink underlying neurobiological mechanismsto human perception. However, brain imag-ing techniques provide another avenue bywhich human perception can be studied,by identifying the brain regions that are activated during the perception of sensorystimuli28,29.When coupled with psychophysicalexperiments, these techniques can provide awealth of information regarding the corticalprocessing of sensory data that results in aparticular percept and the inherent reward orcost that is associated with consumption30.Functional magnetic resonance imaging(fMRI) has recently been used to show thatareas of the brain thought to be involved inthe affective/ hedonic component of olfactorystimuli might process stimulus intensity31.Similarly, positron emission tomography(PET) has been used to identify changes inbrain activity that follow the consumption ofchocolate to beyond satiety30. These studiesare limited by their temporal and spatial resolution as well as the need to limit extra-neous sources of stimulation. However, withcontinued improvement, brain imaging holdsgreat promise in its ability to unlock some of the fundamental questions of sensory neuroscience. If external biases can be incor-porated into the testing model, brain imagingtechniques might provide the food, beverageand consumer product industries with mech-anisms to identify the sensory, hedonic andaffective neural profiles that are associatedwith the consumption or use of a specificproduct.

Perplexing issuesMany questions that are fundamental tohuman sensory science and the food andwine industries can be addressed by usingneuroscientific techniques. The mechanismsunderlying many phenomena that areobserved in human sensory studies areunknown, but mechanistic neurobiologicalstudies might elucidate the neural correlatesthat are responsible for these puzzling observations.

such as electrophysiology and gene-targetedanimal models, provides the additionalcapacity that is necessary to determine howthe initial signal is transformed into a mean-ingful percept. Ensemble14 and chronic15

recordings from sensory neurons along theneuraxis have provided the power that isnecessary to determine how taste, olfactoryand somatosensory stimuli are coded.Moreover, these and similar techniques canbe used to study the cross-modal interac-tions that occur during consumption offoods and beverages. Recent studies haveidentified so-called ‘flavour neurons’ in theorbitofrontal cortex that respond to taste,olfactory and somatosensory stimuli16, andseveral groups have shown peripheral17,18

and central19 evidence for a modulatoryinfluence of trigeminal stimuli on gustatoryresponses. The ability to observe the pheno-typic consequences of over- and/or under-expression of particular genes in vivo has provided investigators with key insightsregarding the roles of particular proteins insensation and perception. For example, micelacking the gene that encodes vanilloidreceptor-1 (VR1) consume equal volumes ofwater and solutions containing the irritantcapsaicin20. Unexpected results from suchexperiments also provide insight into thenative role of the gene product. When thegene encoding α-gustducin, the G-proteinthat regulates bitter taste transduction, wasdeleted, mice showed reduced behaviouraland electrophysiological responses to bittersubstances21. That these animals did not loseall sensitivity to bitter compounds under-scores the complexity and inherent redun-dancy that is necessary to maintain adequategustatory performance. However, there wasalso a marked reduction in sensitivity tosolutions containing sweeteners, indicatingthat gustducin is also important in the transduction of sweet taste sensations.

Finally, the highest levels of neural processing can be studied using various techniques in both animals and humans.Because animals cannot describe the sensations they experience under various conditions, behavioural experiments must be designed so that the perceptions can beinferred. Moreover, the variable that is measured in behavioural experiments oftenreflects the integrated response to intensity,quality and preference, making inter-pretation of the results more difficult.Nevertheless, behavioural experiments intaste22,23 have provided a wealth of informa-tion regarding the neurobiological underpin-nings of aversion and other taste-relatedbehaviours. Psychophysical experiments can



brainstem trigeminal complex also increasesand decreases under similar stimulation pro-tocols45. Moreover, at the molecular level,desensitization of the capsaicin receptor,VR1,has been shown to be calcium dependent12

and probably to involve the phosphatase calcineurin46. Capsaicin-evoked sensitization,on the other hand, has been proposed tooccur either through increased sensitivity ofperipheral and/or central nociceptors, orthrough spatial recruitment44. Little is knownabout the mechanisms by which other irritants evoke sensitization or desensitiza-tion. Specific studies are needed to determinethe cellular and molecular mechanisms thatmediate the sensitizing and desensitizingproperties of these chemicals.

Taste–taste interactions. A number of tasteinteractions in which the presence of one tastant alters the perception of a second havebeen described. For instance, sweeteners areoften added to consumer products to maskbitter or sour tastes. Other examples includethe synergistic interactions that occur for some sweetener combinations47 and for mixtures of L-α-amino acids and 5’-mono-nucleotides48. Recently, the psychophysicalfinding that acids suppress sensations of salti-ness49 was explained by the ability of intra-cellular protons to reduce the influx of Na+

through specific channels expressed on theapical endings of taste receptor cells50. Furtherstudies are needed to explain the interactionsthat are observed psychophysically betweenvarious taste or odour compounds.

Cognitive interactionsTaste and smell. Descriptive analysis of codedsamples provides a representation of percep-tion of the sensory properties alone, withoutthe biasing influence of external factors. Thisoverall perception of flavour does not resultfrom a simple addition of the perceivedintensities of the separate stimuli. The terms‘cognitive interaction’ and ‘cognitive enhan-cement’ have been used to describe interac-tions that occur in perception of multimodalstimuli. In human sensory studies, interac-tions between aroma and taste have beenshown to occur when a model solution, wineor food is tasted, as well as when the taste andaroma stimuli are delivered simultaneouslybut separately51. For example, addition ofaspartame to red wine decreased astringencybut increased sweetness and retronasally perceived ‘berry-fruity flavour by mouth’52.Similarly, the addition of sugar to white wine (A.C.N., unpublished data) or a fruityflavoured beverage increased the intensity of ‘fruitiness’53. Increasing the concentration

trigeminal pathways in these animals couldmake it possible to determine the extent towhich PROP-related genetics influences theperception of tastes and trigeminal sensations.

Carry-over. In the interests of time andmoney, subjects participating in sensoryexperiments are often asked to make severalproduct evaluations during a single session.Many products produce substantial carry-overeffects that can alter the magnitude of sensa-tions being evaluated in later trials comparedwith single-trial evaluations. Various termshave been applied to these phenomenaincluding sensitization, carry-over, adaptation,habituation, desensitization, tachyphylaxisand fatigue; differences and similaritiesbetween these terms have been discussed pre-viously38. The ubiquity of these phenomenathroughout sensory science necessitates agreater understanding of their mechanisms.

The perceived bitterness of many bever-ages, including cider and beer, increases withsuccessive sips. A direct test of this pheno-menon using model solutions found thatdespite rinsing, stimulation with bitter-tastingcompounds increased the bitter intensity thatwas elicited by subsequent bitter compounds39,although the degree and susceptibility to sen-sitization seemed to be compound specific.For instance, previous evaluation of a caffeinesolution significantly increased the perceivedbitterness for subsequent bitter tastants inc-luding caffeine itself, denatonium, limonin,naringin, quinine and sucrose octacetate. By contrast, pre-stimulation with denatoniumonly increased the perceived bitterness thatwas elicited by subsequent stimulation withquinine and denatonium. Our current knowl-edge of taste transduction mechanisms cannotexplain these findings. Phenomenologicalstudies using animal models are needed toexplain the fundamental processes that under-lie sensitization. Determining whether andhow sequence effects alter cellular responses in studies of taste transduction and coding could provide industrial sensory professionals with the insight needed to minimize these confounding effects.

Astringency is a persistent, tactile sensa-tion that is experienced when consuming anumber of flavanoid phenol-containing bev-erages including cider, juice, tea and red wine.This ‘puckering’ sensation is thought to resultfrom the interaction of astringent com-pounds with salivary proteins40. Subjects withlow salivary flow rates have been shown toperceive astringency more intensely and for alonger duration than high-flow subjects, indi-cating that a higher flow of saliva is moreeffective at reducing friction by restoring oral

lubrication41. The intensity of astringencyincreases with repeated sips42 (FIG. 3) and isextremely difficult to remove with rinsing.Biophysical interactions of astringent com-pounds with oral surfaces have not beenstudied and might also contribute to the perception of astringency. Understanding themechanism(s) by which astringency is perceived and by which other sensations suchas sweetness affect its perception would bevaluable for sensory scientists working in thebeverage industry.

Food and beverages containing oral irri-tants are gaining in popularity. In humans,repeated application of capsaicinoids (cap-saicin, piperine), citric acid or concentratedNaCl elicits an irritant sensation that increasesin intensity. After a short (for example, 5 min)break in stimulation, re-application elicits anirritant sensation that is less intense than thatelicited by the original application. With con-tinued re-application, however, the perceivedirritant intensity increases. These phenomenahave been termed sensitization, desensitizationand stimulus-induced recovery (SIR), respec-tively43. In contrast to capsaicin, other irritants(mustard oil, nicotine, menthol) elicit an irri-tant sensation that only decreases acrosstrials44. For companies marketing consumeritems containing these chemicals, obtainingreliable product sensory information is there-fore quite difficult. A neural correlate for thesensory phenomena of sensitization, desensi-tization and SIR has been demonstratedusing neurophysiological techniques in ratsto show that chemonociceptor activity in the


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Figure 3 | Average astringency intensitycurves for two red wines over time. Arrowsdenote the times at which 10 ml of wine wassipped. Fifteen subjects sipped wines at 25 sintervals and swallowed 6 s after each sip, whilerating astringency continuously on anunstructured line scale anchored by the terms‘none’ (0) and ‘extremely high’ (10). Note theincrease in perceived astringency with repeatedsips. Data are from two repetitions. Modified, withpermission, from REF. 42 (2002) AmericanChemical Society.




genetics influence processing and perception,and contribute to the variation in individualresponses to an aroma or taste. The consumer’sresponse to sensory stimuli is modulated byvarious intrinsic and extrinsic factors, whichare affected by each individual’s experience andcultural biases. Despite recent technologicaladvances in neuroscience for studying percep-tion and cognition, an in-depth understandingof the formation of preferences and ultimatelyof consumer behaviour requires an extensivecollaboration of the sensory sciences withmany other disciplines, from anthropologyand sociology to economics.

Christopher T. Simons and Ann C. Noble are in theSection of Neurobiology, Physiology and Behavior

and Department of Viticulture and Enology,University of California,

Davis, California 95616, USA.e-mail: [email protected] or

[email protected]

doi:1038/nrn1139

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Expectation and experience. Purchase deci-sions are made after the consumer determineswhich product best meets his or her expecta-tions. The information that is used in formingproduct expectations is learned implicitly(without the consumer being aware of thelearning process) and explicitly from previousexperience58. Expectations are further influ-enced by extrinsic factors, such as price andbrand, as well as advertising, expert recom-mendations and situation.Wine for an impor-tant dinner must be good. Buying a wine ‘fordinner tonight’ has lower risk. (As a result, themost valid marketing information is obtainedin surveys in which the purchase choices aremade for specific scenarios.) Expectations can also modulate overall perception: whendifferences between the expectation and thesensory properties of the product are small,convergence occurs and the reported sensa-tions are closer to the expected perceptionthan to the product’s sensory properties59.

Neuroscience methods can be used to provide insight into how expectations affectperception of flavour. Neural imaging ofsubjects that are exposed to stimuli that matchtheir expectation to varying degrees mightindicate where the processing occurs. Forexample, after providing a description of thewine aroma or variety, wines that match the given definition to varying degrees couldbe presented. Similarly, imaging of winenovices and experts during evaluation ofwine could be done to examine the influenceof experience on perception. A more subtleexperiment could be conducted in whichwinemakers evaluate commercial wines, atleast one of which is their own. It would beinteresting to compare the neural profiles inresponse to familiar and unfamiliar wines.

Future outlookA more coherent appreciation of the ways inwhich sensory information is processed canhelp the food and wine industries to formu-late and market a successful product. Gilbertand Firestein noted ‘consumer product areas’in which advances in olfaction and gustationcould have an impact60. We agree with theircomments that there are immediate opportu-nities for the practical application of neuro-science in areas such as pest control. However,we are less convinced by their implied directlink from the genomic work to the market.They suggested that biologically based scentmarkers would be a marketing dream.Certainly neuroscience and human sensoryscience, working together, can make enor-mous advances in our understanding of howneural signals are processed to form a coher-ent percept. However, factors other than

of fruity essence has been found to increasesweetness intensity in beverages (A.C.N.,unpublished data), whereas the sweetness orsourness of flavoured solutions was increasedor decreased depending on the nature of theflavour essence54. Murphy and Cain coined the term ‘taste-referred olfaction’ to describethe phenomenon of odour affecting taste55.

Cognitive interaction might partly explainthe results of a sensory-instrumental study inwhich the perceived mintiness of chewinggum was rated continuously56. At the sametime, the concentrations of menthone in thenasal passage and of sucrose in the oral cavitywere monitored. The intensity of mintinessdecreased over time as the concentration ofsucrose diminished, even though a high con-centration of menthone was still present in thenasal passage. Fatigue, desensitization and/oradaptation to menthone probably occurred,but subjects continued to rate ‘mintiness’,which was presumably enhanced by or asso-ciated with the residual sweetness. The sub-jects (who did not rate sweetness separately)might have had a concept of mintiness thatincluded the sweet taste. The subjects’ responseoptions were limited to rating mintiness alone,although both mintiness and sweetness werechanging. Hence,‘dumping’(incorporating thechange in sweetness with the change in mint-iness)57 might also partly explain the results.

Taste–taste interactions, such as betweensweetness and sourness, might be explained inpart by competition at the taste receptor level,but it is not known whether higher processingcontributes to their mutual masking or suppression. By contrast, it is unlikely thattaste–odour interactions occur at the receptorlevel even in the case of compounds that elicittaste, smell and trigeminal sensations such asmenthol or menthone. At least in part, taste–aroma interactions are probably a function ofcognition,occurring at the cortical level16.

Although molecular biology studies haveproduced tremendous advances in ourunderstanding of olfaction, little is knownabout the way in which odour information isultimately encoded to produce a specificaroma perception. Less still is known abouthow meaningful associations between odoursand tastes might be encoded. Examining theneural mechanisms of learning and memorymight provide insight, and brain imaging orother neurobiological techniques might helpto clarify how multimodal information isprocessed. Neuroscience experiments can bedesigned to define what these cognitive phe-nomena represent and to determine theextent to which flavour perception resultsfrom cognitive enhancement, taste-referredolfaction and/or dumping.



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Online links

DATABASESThe following terms in this article are linked online to:LocusLink: http://www.ncbi.nlm.nih.gov/LocusLink/VR1Mouse Genome Informatics: http://www.informatics.jax.org/α-gustducin

FURTHER INFORMATIONEncyclopedia of Life Sciences: http://www.els.net/taste | olfactionAccess to this interactive links box is free online.

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Science and society: Challenges for the sensory sciences from the food and wine industries

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