Leaving a bad taste

Some emotion researchers suggest there are only a very small number of universal emotions: fear, anger, happiness, sadness, surprise, and disgust (see October, 2013: http://prescotttastematters.blogspot.com.au/2013/10/feeling-all-emotional.html). All other emotion terms, in this view, reflect these basic emotions. But even if you are inclined to believe that there are dozens, if not hundreds, of distinct emotional states, there remains one common indivisible emotion, disgust. Disgust sits alone in the cathedral of emotions, shunned even by dislike, guilty and worried. When talking about emotions elicited by foods, the uniqueness of disgust is rather …. unique, in that it is the only emotion that specifically implies a relationship to our sense of taste.

But, of course, foods are not supposed to disgust us, and fortunately most of us seldom come across examples of foods that do. Moreover, although our potential experience and expression disgust is innate, we need to learn what things should make us disgusted. It is a familiar enough scenario where a mother mimics the classic disgust face to a child about to eat something they have picked up from a footpath. With just a wrinkle of the nose, a baring of the upper teeth and a gaping mouth (and perhaps a “Yuk!”), the mother teaches the child a lesson about the potential dangers of otherwise edible items contaminated by …. who knows what, but certainly something that might cause disease. This common sense view is generally supported too by theoretical accounts of the evolutionary purpose of such a strong emotion which stress its role as disease-prevention mechanism [1].

Indeed, we could argue that disgust – despite the origins of the word – has little to do with taste or foods per se. Paul Rozin has characterized disgust as the emotional aspect of fear of contamination through, in the case of foods, consumption. Hence, food is just one of those things that we stick in out mouths that could potentially cause us harm via contamination. It is easy to show that food likes and dislikes show an inconsistent relationship to disgust. So, foods that are highly unpleasant, for example by being bitter, do not necessarily, or even often, induce feelings of disgust.  And, of course, it is possible for us to recognize that foods from other cultures could potentially taste great and be full of important nutrients, even if the idea of them caused a distinct shuddering of the spine.

We can see an illustration of this in the recent enthusiasm for insects as potential food sources in the future. A small, but growing, movement is examining how best to take advantage of the nutrients that insects can provide, and considering how best to deal with consumer responses to this [2]. Because of this interest, which is strong in Denmark, I was recently treated to a lunch provided by the Nordic Food Lab (www.nordicfoodlab.org), in which the menu contained a dish labeled “Peas and Bees”. The label was perfectly descriptive, and I managed to overcome my urge to say “thank you, I’m already full”. Those expecting little yellow and black highlights against the green background would have been disappointed, however, as only bee larvae were used.

Disgust doesn’t always require extreme foods or obvious contamination. Perfectly clean, everyday foods in perfectly clean bedpans will do it, as will being offered a glass of water into which a plastic model of a cockroach has been briefly dipped. In an earlier posting, I noted the extreme reactions to a choc-mint flavoured potato crisp (November, 2013: http://prescotttastematters.blogspot.com.au/2013/11/colour-me-minty.html). In many respects, this response to violation of expectations is a co-opting of so-called core disgust (that is, associated with ingestion of a potential contaminant) to cover a situation in which the unpredictability of the flavour could be a signal for possible danger.

A broadening of the disgust emotion to include those situations where contamination in the physical sense is not a risk is also evident. We talk, for example, about being disgusted by violence or by someone’s behavior or their appearance or their table manners. At least some of these reactions can be included under the term moral disgust. Rozin [3] suggests that the disgust emotion began life as an extension of our in-built responses to bitterness to which we added a cognitive appraisal of other (whether bitter or not) substances that we did not want to consume. This allows us to learn what to be disgusted by as a function of culture or violated expectations. Similarly, strong violations of beliefs, values or rules have become ‘attached’ to disgust. While we might just be using disgust as a metaphor in such situations, there is evidence that it is something more fundamental. Thus, in the same way that the classic disgust facial expression shares common features with facial expressions to unpalatably bitter foods, it can be shown that both core disgust and the moral disgust at being treated unfairly in a game activate a very similar set of facial muscles [4]. So, at least the expression of disgust appears to be highly similar.

A later study looked at associations between bitterness sensitivity, reflected in PROP taster status (May, 2013: http://prescotttastematters.blogspot.com.au/2013_05_01_archive.html), and different questionnaire scales of disgust sensitivity [5]. By distinguishing between different types of disgust: visceral (related to disease, bodily fluids and sexual activity) and moral, the study was able to show that those most sensitive to the bitterness of PROP (supertasters) were also significantly more sensitive to visceral disgust - that is, involving the possibility of contamination through ingestion or otherwise - but not moral disgust. It is possible therefore that the link between core disgust and moral disgust is merely semantic or metaphorical. An alternative explanation, however, is that (as suggested above) that across the two stages or jumps from bitterness responses to core disgust to moral disgust, the link between taste reactivity and moral disgust is weakened or lost.

In either case, examining the origins of moral disgust provides further opportunities to consider the possibility – raised in the previous two postings – that the source of many of our more complex emotional or personality traits can be found in quite fundamental early taste experiences.

                                                                                                                       

1.          Oaten, M.J., R.J. Stevenson, and T.I. Case, Disgust as a Disease-Avoidance Mechanism. PSYCHOL. BULL., 2009. 135(2): p. 303-321.

2.          Verbeke, W., Profiling consumers who are ready to adopt insects as a meat substitute in a Western society. Food Qual Pref, 2015. 39: p. 147-155.

3.          Rozin, P., From Oral to Moral. Science, 2009. 323: p. 1179-1180.

4.          Chapman, H.A., et al., In Bad Taste: Evidence for the Oral Origins of Moral Disgust. Science, 2009. 323: p. 1222-1226.

5.          Herz, R.S., PROP Taste Sensitivity is Related to Visceral but Not Moral Disgust. Chem. Percept., 2011. 4: p. 72-79.

Fear of frying

In my last post (July, 2014: A Taste of Emotion), I suggested the possibility that responses to tastes were linked to other emotional responses not merely by association to some third, common factor, but rather that variations in taste responsiveness might be the cause of different degrees of disinhibition (defined as inability to delay gratification) or how much we react to emotion-inducing stimuli of all kinds. Speculation is fine but how do we establish that one thing has caused another? Proving causal links between any two phenomena is always difficult, but we can ask what sort of evidence might make us take an idle speculation more seriously, even in the absence of absolute proof.

My own first question was whether we had any evidence that variation in taste preferences – apparently uniform at birth – emerges relatively early. If it does, then this can potentially be an influence on subsequent emotional development. This search sent me to the bowels of my dusty reprint archives (more strictly, the Endnote^tm program on my computer). The answer is that there is such evidence, at least when we consider sweetness preferences.

The strong preference for sweetness seen at birth starts to decline as the infant reaches the second half of their first year, such that some infants become relatively indifferent to sweetened water [1]. What does increase is variability in response to sweetness and a plausible hypothesis is that this is a consequence of differing exposures to a variety of foods, only some of which are sweet. And there is evidence for this. Infants fed sugar water prior to 6 months maintained a high preference for sweetness in water at 12 and 24 months. In effect, at 2 years of age, these infants were “sweet likers” (see: February, 2013: How sweet it is …. Or is it?). In contrast, those never fed sweet water did not show a strong desire to drink sweetened water over plain water [2]. Hence, one consequence of the practice of feeding infants sugar water is that is maintains the same high preference for sweetness that exists at birth into their second and third years.

Secondly, is there any evidence that taste experiences are linked to other emotions? Again, some of the “side effects’ of sweet tastes suggests that there might be. We know, for example, that sweet tastes can pacify an infant when they are receiving a painful hospital procedure [3]. The mechanism is not exactly certain but is likely to involve the activation of reward/pleasure pathways that inhibit pain. The reason that some mothers administer sugar water is presumably to help pacify their distressed infant. Through such pairings, the infant will learn to associate demands with reward – perhaps a precursor of later inability to inhibit immediate gratification.

But taste hedonics is not the only potential early influence on later emotions. One other obvious food-related candidate that may influence emotional development is food neophobia (FN). When seen in children, typically those aged 2 - 6 years, it is interpreted as an adaptive developmental stage that limits ingestion of unfamiliar, and therefore potentially dangerous, items that might be mistaken for food. It is thought to be mediated by the fear that unknown foods might taste unpleasant [4].

FN varies with a number of different factors (age and education, for example), and can be modified by experience with food variety. It also differs between cultures: in one study, consumers in New Zealand were shown to be on average more FN than a similar group from Japan. Dietary variety, or at least an attitude towards dietary variety, would seem to be the most logical reason for such differences. Nevertheless, FN is a strongly heritable trait [5] that persists into adulthood in substantial proportions of the population – up to 50% in some estimates. 

As in children, high FN adults have low dietary variety and show a reluctance to consider new foods – even if they are simply new versions of something already eaten.  They also dislike larger numbers of foods than their low FN neighbours. For the high FN individual, therefore, eating is associated with either boredom with the limited horizons of their diet or anxiety at the prospect of encountering something unfamiliar (or perhaps both) – in either case, food generates a relatively low level of pleasure compared to that experienced by the rest of us.

If basic tastes such as sweetness and bitterness elicit some of the very earliest post-partum emotions, then pleasure in our early years is clearly also heavily reliant on food. Rewards are often food based – the ice-cream or cake treat – and it is in these early years that children start to associate particular foods with other rewarding experiences, such as a trip to the well-known McDougalls Scottish burger ‘restaurant’ (Slogan: “It could be worse!”). Presumably for the highly FN child or adolescent, there is no such thing as being “pleasantly surprised” by food.

But there are many things about the FN experience that are unknown. How does the development of preferences for new foods develop in high FN individuals? Do high FN diets exclude whole categories of foods? One example might be very spicy or bitter foods, the consumption of which requires tolerance for initially unpleasant qualities (remember that FN is mediated by a fear that something with taste unpleasant). Rozin has suggested that the single most important question that can be asked of someone if you wish to know their food preferences is “what is your culture or ethnic group?”. It may be the follow-up question ought to involve measuring FN.

Strong evidence is lacking for an effect of FN beyond the food domain. However, more general personality traits such as sensation seeking are based on a broad enjoyment of novelty as well as “thrill seeking” in a variety of contexts. On another occasion, Rozin proposed that eating chilli might be a form of benign thrill seeking and so the question remains as to whether early failure to thrill seek with foods may predispose the individual to adopt similar approach when faced with novel experiences in general. 

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1. Schwartz, C., S. Issanchou, and S. Nicklaus, Developmental changes in the acceptance of the five basic tastes in the first year of life. Br J Nutr, 2009. 102(9): p. 1375-85.

2. Beauchamp, G.K. and M. Moran, Acceptance  of sweet and salty tastes in 2-year old children. Appetite, 1984. 5: p. 291-305.

3. Blass, E.M. and L.B. Hoffmeyer, Sucrose as an analgesic for newborn infants. Pediatrics, 1991. 87(2): p. 215-218.

4. Pliner, P., M. Pelchat, and M. Grabski, Reduction of neophobia in humans by exposure to novel foods. Appetite, 1993. 20: p. 111-123.

5. Knaapila, A., et al., Food neophobia shows heritable variation in humans. Physiol. Behav., 2007. 91: p. 573-578.

A taste of emotion

If you study perception, you tend not to be particularly concerned with the “secondary” emotions that sensory experiences might evoke (for a fuller discussion of this, see: http://www.expo.rai.it/eng/2014/07/08/taste-neuroscience-prescott/). Except if you study taste, in which case you can hardly avoid it. Emotional responses to tastes are, we can say with a reasonable degree of certainty, built into the fabric of the taste experience. Jacob Steiner’s famous photographs of newborns smiling or grimacing in response to sucrose and quinine [1], respectively, are if not exactly proof of this, then nevertheless compelling. The adaptive argument, too, is simple: tastes evoke emotions because this activates motivations to consume (calories, salt) or avoid (toxins) and hence promote survival. 

Our everyday language provides us with some hints that taste may find links with our emotions more broadly. Thus, unpleasant emotional experiences will leave a bitter taste in your mouth; we say that we can taste the fear, and of course sweetness is synonymous with all sorts of pleasant emotions.  The usual interpretation of such figures of speech is that we have co-opted tastes to help us describe emotions, perhaps because we tend to be poor at this.

But increasingly this does not seem to be the whole picture. A recently published study by Herbert and colleagues [2] examined the way in which autonomic nervous system responses - eye-blinks and changes in pupil diameter in response to startling bursts of white noise - are modified by emotion-inducing pictures. Importantly, though, they compared these responses in tasters and non-tasters of the bitter compound 6-n-propylthiouracil (PROP). This study was prompted by an earlier study in which PROP supertasters showed more intense self-reported emotional responses (anger, tension, sadness and fear; decreased mood and joy) than non-tasters or medium tasters after an anger-inducing film clip.

Herbert and colleagues found that startle responses were increased for pictures meant to elicit fear, anger, disgust, or pictures that were pleasant in content, relative to neutral pictures – but in the PROP-taster group only, and not the non-tasters. This suggests that the PROP tasters are hyper-responsive to both negative and positive emotions generally, not just to tastes.

Why would broad emotional responsiveness be linked to the ability to taste a particular bitter compound? Certainly, facial expressions to bitterness – the familiar grimace, nose-wrinkle and gape – has previously been thought to be the basis of the classic disgust facial response and perhaps even the origin of this basic emotion itself. Indeed, PROP super-tasters has been shown to be more responsive to the visceral – but not moral – aspects of disgust than are (medium) tasters and non-tasters, with taste sensitivity being positively correlated with degree of disgust [3].

But a common origin for disgust and bitterness dislike suggests something broader than the involvement of one particular bitter compound linked to a specific taste receptor (T2R38), one of perhaps 30 or more such bitter receptors. Two possibilities suggest themselves. The first is that responses to bitterness in general are reflective of an underlying overall emotional responsiveness, a relationship yet to be tested. In this sense, bitter substances are simply effective at eliciting emotions, in the same way as pictures of disgusting scenes or objects are effective. In addition, though, ratings of PROP intensity are often used as a proxy measure for taste responsiveness in general. PROP tasters also find sweet, salty sour and bitter tastes more intense than do PROP non-tasters (see for example, [4]).  This is more than likely due to the fact that increased numbers of taste buds underlie overall taste responsiveness, including (at least for those not ‘blind’ to it), PROP bitterness.

It has been hypothesized for some time that the pleasure given by sweetness is really no different than pleasure of any other sort, and that a common reward system in the brain underlies the popularity of sex, drugs and rock ‘n roll ….. and cake. But yet another broad link between taste and more general responsiveness to reward has been reported [5]. I have discussed the phenomenon of sweet liking and disliking previously (How sweet it is ... or is it?). The origins of this hedonic dimension are not well understood, but this study suggests that it may be linked to variations in overall disinhibition. Here, disinhibition was defined in terms of delay discounting – the idea of how much we value a given reward given now versus one that may be much larger, if we are willing to wait for it. So, if I say that I would rather have $10 now rather than $20 in a month, I am effectively discounting the later amount. In food terms, I can have one piece of chocolate now or three pieces in an hour. If you opt for the smaller reward now, you are unable to inhibit your need to satisfy your immediate desire. It turns out that such “discounters” are more likely to be sweet likers, that is, to prefer higher levels of sweetness. This then is another case of taste responses being seen in terms of more general responsiveness to reward.

An obvious interpretation is that, as mentioned above, pleasant tastes are merely part of an overall reward system that has adaptive value. However, there is an intriguing alternative explanation of why tastes might be so tied into other aspects of emotional life. If we start with the premise that tastes are responsible for some of the earliest emotions that we experience, it becomes possible to think about these early experiences having a large impact in shaping our broader emotional landscape. So, in this scenario, the fact you respond more positively to sweetness than I do becomes a major factor in whether or not you delay discount, not just for chocolates but in general for all reward. Similarly, sensitivity to bitterness – present at birth – has such a strong emotional impact that it influences the way you subsequently respond to all emotional stimuli. As a corollary, individual variations in taste sensitivity or hedonic value becomes a primary determinant of variations in our emotional responsiveness generally. 

Admittedly, this is a “chicken/egg” argument that may be impossible to determine but ….. the chronological primacy of taste hedonics does mean that we ought to consider the possibility that the taste of fear is not a way of helping us describe emotions but rather a clue to where our emotions originate.

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1. Steiner, J.E., et al., Comparative expression of hedonic impact: affective reactions to taste by human infants and other primates. . Neurosci. Biobehav. Rev., 2001. 25(1): p. 53-74.

2. Herbert, C., et al., Supertaster, super reactive: Oral sensitivity for bitter taste modulates emotional approach and avoidance behavior in the affective startle paradigm. Physiol Behav, 2014. 135C: p. 198-207.

3. Herz, R.S., PROP Taste Sensitivity is Related to Visceral but Not Moral Disgust. Chem. Percept., 2011. 4: p. 72-79.

4. Prescott, J., N. Ripandelli, and I. Wakeling, Intensity of tastes in binary mixtures in PROP non-tasters, medium-tasters and super-tasters. . Chem. Senses, 2001. 26: p. 993-1003.

5.    Weafer, J., A. Burkhardt, and H. de Wit, Sweet taste liking is associated with impulsive behaviors in humans. Front Behav Neurosci, 2014. 8: p. 228.

The subtext on context

“What’s the weirdest food you have encountered?”. I suppose that’s a reasonable question if you write about food preferences – we all are fascinated by the unusual. And it is why I opened Taste Matters [1] with a description of hakarl, the (to me) repulsive Icelandic dish made from rotten shark meat. My more general answer, though, is usually disappointing: any food – including what you ate for lunch today – can be weird, depending on whom you ask. If rotten shark meat is a delicacy, who’s to say that roast chicken, or oysters, or flat bread topped with tomato, cheese, and tiny fish won’t seem like odd things to eat.

It is all about context. As food consumers, our focus is naturally on the foods that we eat. Are they tasty, healthy, interesting and so on? But if you shift focus from the food to consumers themselves, it becomes apparent that all responses to foods – likes, dislikes, strangeness - are relative …. to something. Even the question of whether a taste is strong or weak is only partly based in the food itself. Is your coffee very sweet? That’s merely a function of how much sugar you normally add to it – in other words, your memory of how sweet coffee should be. Is the dish too spicy? Probably not, if it is similar to what you normally eat. Your accumulated memories of what you have eaten, and in particular most recently eaten, provide an internal context against which a food or flavour can be said to be weak or strong, and hence pleasant or unpleasant.

Similarly, our past experiences with foods and the combinations of tastes, aromas, textures and colours that typically occur lead to expectations prior to eating. Violating these expectations can lead to a variety of outcomes, depending on the context. At a purely perceptual level, it is easy to demonstrate that a lime-flavoured drink will be identified most often as berry-flavoured if it is coloured red. On the other hand, a colourless drink will be judged as less intense in flavour. We tend to trust our eyes more than our ability to identify flavours. Such demonstrations can be a source of embarrassment when this is done with wine enthusiasts, who will talk at length about the cherry, blackberry and tobacco notes of a white wine to which red food colouring has been added. 

Confounding expectations is not always a bad thing. A favourite traveller’s tale concerns the tiny restaurant found in a back alley of a small town off the beaten track in an exotic location. The seating was fruit crates, the waiter spoke only the local language, and the kitchen wasn’t large enough for two people. The food, however, was sensational and produced an enduring memory of a great meal experience. Of course, we can have great meal experiences at Michelin-starred restaurants in major cities, but it is the surprise element – the wonderful flavours despite the context – that provide both the additional pleasure, and a way of locking it into our memory. Moreover, our surprise meal transported to a different context – say, a plush restaurant with formal service – is far less likely to be memorable precisely because our expectations for fine food were met exactly. Consumer scientist Herb Meiselman showed some years ago that the pleasantness of the same meal would be judged quite differently served in different contexts such as a restaurant, a canteen or in a hospital setting [2].

Part of the enjoyment of our exotic-location meal derives, of course, from the idea of authenticity. The food takes on an added pleasure if we feel that we are experiencing what the locals experience. This is such a common pursuit these days that authenticity – real or perceived - becomes a selling point and sometimes also a way of subtly pushing us towards particular food choices. What’s more appealing: long noodles with meat sauce or tagliatelle a la Bolognese? One is just a meal but the other is an ethnic meal (unless you are from Bologna, of course). And what would you rather drink with it? Even if you can afford to order a nice Burgundy, doesn’t the idea of the unknown local red wine – the owner’s selection – draw your interest just that much more? A great wine versus a wine experience.

The influence of a context doesn’t have to be subtle. Most people can convince themselves about the added appeal of a meal in a restaurant in which a few cultural stereotypes are on display over the same meal cooked at home or in a generic restaurant environment. Rude waiter – check. Brass fittings – check. Edith Piaf soundtrack – check. Yes, this is not a steak, chips and wilted lettuce leaf, it’s a genuine steak frites. Sophisticated and worldly diners might expect themselves to be immune from such obvious influences: their focus is on the food, the technique, the playful presentation. But the cues to context that set up expectations are not necessarily open to conscious inspection. One study, for example, examined the impact of playing French or German style background music on alternate days in the wine section of a supermarket [3]. Despite the fact that when questioned, consumers were unaware of the type of music being played, German and French wines were more often purchased on days when German and French music, respectively, was played. The researchers’ quite plausible explanation is that the music activated other, unconscious, nationality-based associations that nudged the consumers towards the purchase of a wine that was congruent – that is, a good fit – with those associations.

This idea helps explain too how wonderful food or wine in one context totally fails to impress when removed to a different context. Sitting in the sun, watching the ocean, a piece of grilled fish on the plate and a glass of local wine in hand seems a perfect combination. Remove the sun, ocean and carefree thoughts, however, and the same wine seems like a very odd purchase to have brought home from holidays. These important contextual cues are now being explicitly utilized by some chefs who have recognized that eating is a multisensory experience, the pleasure of which is enhanced by an environment that stimulates our senses and activates memories of past experiences. A well-known example of this is apparent in a dish entitled “The Sounds of the Sea”, created by British chef Heston Blumenthal [4]. The diner listens to the sound of waves on the shore (via an iPod hidden in a conch shell) to accentuate the visual presentation of seafood on a tapioca-based ‘sandy beach’, with a vegetable and seafood based foam as the rolling waves. The result is a multisensory immersion in sights, sounds, odours, textures and tastes with contributions from memories and emotions that evoke warm feelings of nostalgia for days on the seashore. 

An ethnic theme in a restaurant may influence our food selection and enjoyment, but our actual culture is really the key context through which food preferences are formed and foods are interpreted. Around 30 years ago, food psychologist Paul Rozin and his wife, food writer Elizabeth Rozin, formulated the idea of culturally-based flavour principles by asking two important questions [5]. The first of these was whether each culture’s cuisine could be defined in a list of key ingredients and cooking styles that distinguished it from all other cuisines. Essentially, what they wanted to know was what made Italian food Italian or Greek food Greek and, for example, if we ate a chicken dish each from Italy, Spain and Greece, what would be the essential features that would allow us to know their origins.  After all, each of these cuisines uses olive oil, garlic and tomato in their cooking, so they are in many ways similar. But we can still see differences between them in the use of different herbs and spices such as oregano, basil, rosemary, chilli, paprika, saffron, thyme, parsley, fennel and so on. Even when there is overlap in the types of spices used, there will be different combinations and emphases in the cultures for different dishes. Of course, when cultures are geographically more remote, or the history of influences is dramatically different, the differences in flavour principles become more obvious. 

Secondly, the Rozins asked whether flavour principles might have some purpose, other than being merely a matter of convenience is using whatever ingredients were locally available. They proposed that flavour principles actually performed a vital, biologically important function (apart from making chicken more interesting to eat). They recognized that all of us tend to be rather wary of incorporating new foods into our diet – the scientific term is food neophobia – an evolutionary hangover from our time in the wild where new plants could as often be poisonous as nutritious. But given that even in more modern times, the environment is not always friendly to food sources, and it pays to be flexible and be able to incorporate new sources of proteins and plant foods in the diet. Cooking in a familiar way, with familiar ingredients, converts a potential source of neophobia into a recognizable dish that is more likely to be accepted than rejected as unfamiliar.

The members of each culture learn that the flavour is the acceptable context for the various ingredients that provide sources of protein – whether it be chicken, fish, insects, rotten shark, tripe – and other nutrients. And this learning takes place even before we are born. Research over the past two decades has shown that flavours are passed from a mother’s diet into the amniotic fluid surrounding a foetus. Importantly, this provides exposure to, and hence familiarity with, these flavours that can be seen in the preferences of the baby at the time of weaning. Foetal exposure to the flavour of a vegetable such as carrot will mean that carrot flavour is more readily accepted even when the infant is 2 years old. Of course, what the mother is doing is inadvertently passing of culturally-based food knowledge: the flavour principles of the mother’s diet become those of the infant. The culture of food thus is transmitted from generation to generation - but how such transmission will survive globalization of foods is unclear.

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1. Prescott, J., Taste Matters. Why we like the foods we do. 2012, London: Reaktion Books.
2. Edwards, J.S., et al., The influence of eating location on the acceptability of identically prepared foods. Food Qual Pref, 2003. 14: p. 647-652.
3. North, A.C., D.J. Hargreaves, and J. McKendrick, The influence of in-store music on wine selections. J Appl Psychol., 1999. 84(2): p. 271-276.
4. Blumenthal, H., The Big Fat Duck Cookbook 2008, London: Bloomsbury.
5. Rozin, E. and P. Rozin, Culinary themes and variations. Nat. Hist., 1981. 90(2): p. 6-14.

Nose-ology of smelling

Just how important is our sense of smell? None of us wants to lose any of our senses, but ranking them in order of importance will for many people put smell into the lower half of the list. This is certainly reflected, for example, in compensation payouts where the lost of an eye, or partial deafness, is weighed far more heavily than total smell loss. Such figures are worked out in a world in which survival no longer depends on sniffing out our daily meal. But I wonder if, in the developed world at least, old ideas about the importance of smell have not kept pace with our recent obsessions – both nutrition and flavor related – with food.

It has been obvious for some time that the key to flavour characteristics is a food’s aromas. The OED, for example, notes that the word flavour in English, thought to date from the late 14^th/early 15^th century, originally referred only to a fragrance or aroma. A figure of 80% is often quoted as the contribution that odours make to food flavours. This is not based on actual data, but is rather an attempt to convey smell’s importance. Less quantitative, but more to the point, is the fact that with our sense of taste alone we are generally unable to identify foods and beverages – as we often witness when the sense of smell is disabled by nasal congestion. From the point of view of flavour, a food without an odour is no more than a nutritional supplement.

Knowing this, you might think then that our sense of taste is the one to loose (if we had a choice) and wanted to continue to enjoy food. It is fortunate, however, that total taste loss is relatively rare since when it occurs its effects are reported to be at least as, if not more, devastating to food enjoyment as is smell loss. 

In contrast, major smell loss is relatively common and is associated with a wide variety of social and health problems, including loss of enjoyment of food leading to altered eating patterns, depression, and increased concerns about hygiene and household safety. Interestingly, while the acquisition of a sensory loss of any type might be expected to produce such effects, it has been reported that individuals who have never had a sense of smell also report many of these problems [1]. Compared to healthy controls, a group of such congenital anosmics reported more household accidents, increased concerns about social interactions, and higher depression scores. Their eating behavior was, however, similar to that of the normosmic controls. This suggests that dietary changes following smell loss are primarily due to a lack of interest in foods as a result of their sudden ‘tastelessness’ or attempts to overcome this problem by, for example, boosting flavor using salt or sugar or other detectible qualities.

Smell loss is also common as we age, although it appears that this often goes unnoticed because of its gradual onset, while eating patterns are preserved due to habit. In fact, suddenly acquired total smell loss does not always produce a dramatic impact on food choices. As with aging, this may reflect the preeminent role of habit in the diet of some individuals. However, first hand reports of those suffering anosmia acquired as a result of head injury or nasal disease include examples of individuals who say that they can recall food flavours and essentially “fill in the gaps” left by the lack of food odour.

The ability to generate such olfactory imagery has been somewhat contentious, but there is now good evidence that some people can generate mental images of odours, even if they tend to be more fleeting and weaker than visual images. So-called good olfactory imagers – based on self-report – actually sniff when imaging odours, and their sniffs are larger (more air inhaled) when imaging good than bad odours, exactly what is found with sniffs in response to a physically present odour [2]. Imagined odours have recently been reported to enhance the ability of a food picture to induce salivation, and to influence the actual amount consumed of a palatable food [3]*. An earlier study found that imagined odours enhanced a physically present congruent taste in the same way an actual odour would [4].

So, olfactory imagery can have tangible effects and this is important since olfactory cues are very powerful engagers of food wanting and craving.  Variations in being able to image a food flavor may therefore be crucial to understanding why some individuals succumb to food-related cues by overeating. 

In addition, though, why only some people are able to generate olfactory images and indeed why it is possible to use these to compensate for actual smell loss highlights how surprisingly little we still know about the nature of the information about smell that we store in memory. We know that odour memories seem to be more emotionally laden than other sensory memories. They are also poorly linked to language – no one has the same difficulty identifying a melon by sight as they do in naming it based only on its odour. 

In a recently published theoretical review, Koster and colleagues [5] propose a model of the sense of smell that attempts to account for the apparently odd ways that smells are encoded. These authors point to the fact that, generally, we are mostly unaware of the odours around us – indeed, for most of us, most of the time, our environment is odourless. After a brief period of perception, even novel odours recede out of consciousness due to adaptation. However, this does not mean that that the odour is not encoded. Koster and co argue that odours are ignored without consequence because the encoding is implicit – odours link to events and places incidentally, without conscious effort. The meaning of the odour is supplied by the context in which it was originally experienced. They argue, too, that not only is there no point in asking questions about our ability to identify odours, but that attaching a name to an odour necessarily weakens the link between the odour and its initial context. It is only when an odour is experienced in an unusual context or when expectations about odours are violated do we need to conscious pay attention to them since this may signal something potentially important to survival.

All this may seem odd: that our sense of smell is more about ignoring odours than paying attention to them. However, as Koster et al. note, sensory signals are meant to tell us something important about the world. Information that indicates only that the status quo is in place tells us nothing, while attempting to consciously take in and process such information would be overwhelming. 

Surely though this doesn’t apply to food? We think about food enjoyment in terms of attending to the myriad odours and flavours that make up our diet. But, do we actually do this? A meal at a gastronomy temple may encourage a focus on individual flavours and odours, but did you really pay attention at breakfast today? And exactly what was the quality of peas-ness of your peas last night? On the other hand, if there was an odd flavour lurking in your greens, you can be assured that this will register and possibly help you avoid consuming something nasty.

* This article is notable for one other thing: introducing the worst neologism in recent memory ….. smellizing.

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1. Croy, I., et al., Learning about the functions of the olfactory system from people without a sense of smell. PLoS One, 2012. 7(3): p. e33365.

2. Bensafi, M., S. Pouliot, and N. Sobel, Odorant-specific patterns of sniffing during imagery distingusih 'bad' and 'good' olfactory imagers. Chem. Senses, 2005. 30: p. 521-529.

3. Krishna, A., M. Morrin, and E. Sayin, Smellizing Cookies and Salivating: A Focus on Olfactory Imagery. J. Cons. Res., 2014. 40: p. DOI: 10.1086/674664.

4. Djordjevic, J., R.J. Zatorre, and M. Jones-Gotman, Effects of Perceived and Imagined Odors on Taste Detection. Chem. Senses, 2004. 29: p. 199-208.

5. Koster, E.P., P. Moller, and J. Mojet, A "Misfit" Theory of Spontaneous Conscious Odor Perception (MITSCOP): reflections on the role and function of odor memory in everyday life. Front Psychol, 2014. 5: p. 1-12.

Unaware eating

When was your last memorable meal: last anniversary, birthday, or other special occasion? What about dinner last night at home? While you may actually be able to remember what you ate last night, the details about quantities and how much time you spent eating are likely to be sketchy at best. To a large extent, this is due to the fact that we seldom pay much attention to eating, except perhaps when in a special restaurant, when awareness is part of both the enjoyment and our motivation to maintain a vivid picture of where all that money went. The term “mindless eating” is often used to convey the way in which we consume foods without monitoring the amounts, and has been linked to overconsumption of snack foods and, of course, obesity.

Going back a century or so, Ivan Pavlov was inducing his canine “research participants” to salivate in response to sounds that they had learnt meant that the evening meal was probably on the way. He termed these responses “psychic secretions” to indicate the role of a mental – that is, psychological – process linking the new signal (the sound) to the original stimulus for salivation (the food), rather than an automatic, in-built reflex. At least in humans, it is generally considered that a such learned connections must be conscious – we are not going to salivate to the sound of a bell unless we know that it signals dinner. However, awareness is not an “all or none” phenomenon and it is often the case that, once learning has taken place, we do not pay attention to those cues that induce a desire to eat or that influence what we want to eat or how much we eat.

Two adjacent papers in a recent issue of the journal Appetite show, in quite different ways, how eating can come under the control of cues outside of our immediate awareness. Feel like you are a free agent in your food choices? That you make these choices according to your appetites, or values, or needs? Gaillet-Torrent and colleagues [1] show that pre-exposure to an ambient pear odour induced their participants to more frequently select a fruit-based dessert for their lunch than those who were not exposed to this odour. These researchers argue that the pear odour ‘primed’ a later food choice that was consistent with the odour quality, namely fruit. Consistent with this, there was no impact of the odour on other, non-fruity lunch courses.

Is this a surprise? After all, the smell of chicken roasting obviously influences our desire to consume that chicken rather than, say, a tuna salad. However, the key here is awareness. The odour exposed group showed no indication on questioning that they were consciously aware of the pear odour that had been present in the room in which they waited for the experiment to commence. And the effect was not merely a slight bias towards the fruit dessert. The control group, not exposed to any odour and hence able to provide a measure of the relative attractiveness of the fruit dessert, choose the alternative dessert – a brownie – by a margin of 3 to 1. So the priming odour not only pushed choice towards one dessert but substantially away from one that might have been chosen otherwise.

A tendency to overeat while paying attention to television is well-known as a prototypical example of mindless eating. But it has not been clear why this occurs. Does an engaging TV program simply distract us from actively monitoring what we eat? Lucy Braude and Dick Stevenson [2] studied this phenomenon, asking whether the increased intake was a function of TV interfering with either (or both) the hedonic changes that occur during eating (a decline in liking known as sensory-specific satiety) or the ability to pay attention to our internal cues signaling reduction of hunger or increasing fullness.

The study asked participants to consume either a single snack food or a variety of different snack foods while either watching TV or not. Replicating the already established findings that both watching TV and food variety produced increased energy intake, this study also showed that liking decreased for the food or foods eaten – the effect of sensory-specific satiety (SSS). However, the most interesting aspect of the results was that while, as expected, eating a single food results in a decrease in liking for that food, this decrease only occurred in the no TV condition. In other words, watching TV eliminated the SSS that we would expect to occur. Eating a variety of snack foods, which produces less SSS in any case, was, in contrast, unaffected by TV watching.

While hunger and fullness ratings did not change due to watching TV, intake (as mentioned above) did. Essentially, this means that greater amounts of snack food were consumed while watching TV to produce the same ratings of fullness and hunger as those who did not watch TV. Both this finding and the effect of TV on SSS are interpreted by these authors as reflecting a disruption of our largely automatic monitoring of both sensory pleasure and cues for hunger. Thus, those bits of the mind that watch what we eat are largely absent: true mindless eating.

Both of these studies shed light on the hidden influences that shape what we eat. Overconsumption is a major concern among many populations and the failure of weight-loss diets to work in the long term is well established. It is recognized that part of the problem is that we are constantly exposed to cues (odours, sights, and even sounds) that signal foods and drinks, especially those high in fat or sugar, making it difficult to resist the associated conditioned impulses to eat [3]. Demonstrating that substantial influence over what and how much we consume can be exerted by cues that evade awareness only emphasizes how difficult the process of exerting control over food intake can be. Conversely, of course, active attention to eating ought to be a means of regaining control. The problem is that lifestyles in many affluent countries work against this. It is no coincidence, I think, that my colleagues in France, where for an affluent country there is relatively low levels of obesity, sit down to eat a substantial meal twice a day (see: http://prescotttastematters.blogspot.nl/2012/12/le-topic-du-jour-gout-qui-importe.html). For them, snacking on the run or while watching TV has been relatively rare.

                                                                                                                       

1.  Gaillet-Torrent, M., et al., Impact of a non-attentively perceived odour on subsequent food choices. Appetite, 2014. 76: p. 17-22.

2.  Braude, L. and R.J. Stevenson, Watching television while eating increases energy intake. Examining the mechanisms in female participants. Appetite, 2014. 76: p. 9-16.

3. Ferriday, D. and J.M. Brunstrom, How does food-cue exposure lead to larger meal sizes? Brit. J. Nutr., 2008. 100: p. 1325-1332.