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“You like tomato, I like tamato… let’s call the whole thing off.”
Ella Fitzgerald and Louis Armstrong (1959)
Have you ever noticed that your scent preferences are not necessarily matched by others, or that in some cases you ardently disagree with another’s scent opinion? Why is this so? Is rose necessarily a good smell and skunk a bad one? Are we born with a template of what smells we will like and what scents we won’t, or do our smell preferences develop and change? And why do we not all share the same preferences? The goal of this paper will be to address these questions with the latest scientific evidence and theory and to explain where our odor preferences come from, what influences them, and how they can be changed.
Odor Hedonics
The most immediate and basic response we have to a scent is whether we like it or not. In scientific parlance this is referred to as odor hedonics. Hedonic perception is an affective evaluation that centers on liking; that is our preferences. Pleasantness, familiarity and intensity are the three factors most often evaluated when examining odor hedonic perception. Pleasantness and familiarity are usually highly correlated in odor preference perception, whereas intensity has a more complex relationship to pleasantness (Moskowitz et al., 1976; Sulmont et al., 2002). That is, familiar odors tend to be better liked than unfamiliar odors, and pleasant odors are often perceived as familiar. In contrast, how strong a scent is and how it affects our pleasure of it depends on what the scent is. For example, a weak fishy odor may be acceptable, but not a strong one. However, a stronger lilac scent is usually preferred to a weak one (at least up to a point).
A long-standing debate in theories of olfactory perception is whether hedonic responses to odors are innate or learned. The innate view of odor preference claims that we are born with a predisposition to like or dislike various smells. Though widely held, this view has not been empirically validated in humans and is largely due to extrapolations from animal pheromonal communication (Rasmussen & Schulte, 1998). In contrast, the learned view states that we are born merely with a predisposition to learn to like or dislike smells, and whether we have a preference for a certain smell or not is due to our acquired emotional associations to that scent (Bartoshuk, 1991; Engen, 1991; Herz, 2001).
Associative Learning and Odor Hedonic Perception
Associative learning is at the basis of the learned view of odor hedonic perception. Associative learning is the process by which one event or item comes to be linked to another because of an individual’s past experiences (Wasserman & Miller, 1997). For example, imagine there is a stimulus, call it “A”. Your response to A is A+. Now imagine there is another stimulus, call it “B.” Your response to B, however, is nothing (0). Now put A and B together and what happens? When you are presented with A again your response to it is still A+. However, when you are presented with B again, your response to it is now A+ as well. That is, through association, B, which was formally meaningless has taken on the properties of A. Associative learning is responsible for a large part of human cognition and behavior and is also the foundation of classical conditioning. 1
The associative learning view of odor hedonic perception states that an odor is initially meaningless or a tabula rasa (blank slate) and that through association with the context in which it is perceived it takes on the associations/meaning of that context (Bartoshuk, 1991; Engen, 1991). Specifically, the theory states that odor hedonic perception is formed from a learned association combining the odor and the emotional valence surrounding one’s first encounter with the odor (Herz, 2001; Herz, et al., 2004). For example, a novel odor is first experienced in conjunction with an emotional event that induces anxiety, such as a surgical procedure in a hospital. That odor, through its association with the emotion of anxiety, then acquires the emotional significance of anxiety which imbues the odor with hedonic meaning, and influences its perception (e.g., unpleasant). Thus the reason why “hospital smell” is generally disliked is because of the unpleasant associations we have to hospitals. In contrast, a novel odor experienced in conjunction with someone whom we are passionately attracted to will be imbued with very positive associations and thereby become very pleasant. Thus, the reason why we like or dislike various smells is due to our emotional associative history with the odors in question. Notably, our emotional associations do not always have to come from direct experience; cultural learning provides meaning to many unencountered stimuli. For example, one need not have suffered through a fire to know that smoke signals danger.
When discussing odor preference formation it is important to consider the issue of odor novelty, because if an odor is already familiar, it necessarily has been previously associated to past experiences. It is known that once an association to an odor has been formed it is difficult to re-associate that odor to something different. This was clearly shown in a study by Lawless and Engen (1977) which demonstrated that the first association made to an odor interfered with learning subsequent associations to the same scent (proactive interference), whereas new pairings to the scent did little to over-ride the previous associations made. Therefore, the first associations made to an odor are very powerful. This has important implications for introducing new scents and changing odor preferences once they have been formed (see Direct Experimental Evidence for Odor Preference Formation for further discussion).
Developmental Factors in Odor Hedonics
We are born with a fully functional sense of smell. And newborns have very minimal prior experience. Therefore, if one wanted to examine whether our odor preferences were innate the best place to look would be at infants, because if odor preferences are innate then newborns should display them. However, infants do not respond to scents the same way their parents do. Indeed infants often show opposing responses to adult preferences, for instance liking the smell of sweat and feces (Engen, 1982; Stein et al., 1958). Research with toddlers and youngsters up to the age of five (Engen, 1988) also indicates that this age group often does not differentiate between odors that adults find either very unpleasant (e.g., butyric acid = rancid) or pleasant (amyl acetate = banana) and typically display neophobia as a general response; avoidance of unfamiliar foods/flavors (Frank & Kalisewicz, 2000). Only one study has reported that young children (3-year olds) showed adult-like responses to certain odors which would be in keeping with an ‘innate’ framework (Schmidt & Beauchamp, 1988). However, this research has been criticized on methodological grounds (Engen & Engen, 1997). Notably, by the time a child is approximately eight years old, olfactory responses closely resemble those of the adults in his culture (Engen, 1982).
The developmental literature suggests that olfactory preference learning begins at the very onset of life itself. Indeed our sense of the smell is fully operational by the time we are just three months in the womb (Schaal et al., 1995, 1998; Winberg & Porter, 1998). Mennella and colleagues found that infants of mothers who consumed distinctive smelling volatiles (e.g., garlic, alcohol, cigarette smoke) during pregnancy or lactation showed preferences for these smells compared to infants who had not been exposed to these scents (Mennella & Beauchamp,1991; Mennella & Beauchamp,1993; Mennella, et al., 1995). Additionally, early learned odor preferences go on to influence food and flavor preferences in later childhood (Mennella & Garcia, 2000) and adulthood (Haller, et al., 1999).2 Notably feeding, in addition to providing nutrition, is an opportunity for close physical contact and emotional bonding. Association through affectionate cuddling alone has been shown to induce preferences for specific (yet arbitrary) scents among infants, such as cherry oil or mother’s perfume (Balough & Porter, 1986; Davis & Porter, 1991; Lott et al., 1989; Schleidt & Genzel, 1990; Sullivan et al., 1991). Thus, the developmental literature demonstrates both the lack of a priori hedonic responses to odors, as well as the readiness of the olfactory system to learn the meaning of odors/flavors based on associative learning and the emotional significance of the associated experience.
Although the majority of our odor preferences are acquired during childhood, because of the novelty and salience of so many experiences, any time a new odor is encountered associative learning mechanisms can determine our odor preferences. Anecdotes of liking or disliking scents because of their connection to significant others (Herz, 2001) and idiosyncratic cuisine preferences (Rozin, 1996) are just a few examples of how associative learning and emotional-social context influences odor perception throughout life. The forthcoming section Direct Experimental Evidence for Odor Preference Formation discusses this issue in detail.
(1) Pavlov’s dogs inherently salivated to meat, but a bell meant nothing to them. After a bell had been paired with the presentation of meat several times, the bell alone was sufficient to make the dogs salivate.
(2) Flavor is produced primarily by odor; taste contributes only the sensations of salt, sour, sweet, bitter and savory (Bartoshuk & Beauchamp, 1994). Continue > |
