Olfactory Language: Context Is Everything

The sense of smell, olfaction, is currently in the spotlight. Although often a neglected sense, smell loss and smell distortions due to coronavirus disease 2019 (COVID-19) has increased public awareness of olfaction and its role in health, well-being, and nutrition [1,2]. In this unusual context, Majid [3] provides a timely, well written, and thought-provoking review of olfaction and its cognitive aspects. Majid focuses on how smells are expressed in languages around the world, yet the review covers a vast literature that includes also experimental, cognitive, and biological fields. The thrust of the argument is directed against a perceived dogma; that ‘there is no language of smell and humans are bad at naming odors’. Majid argues that this dogma is refuted by cross-cultural research and concludes that ‘rather than focusing on constrained experimental tasks’, olfactory language should be studied in terms of ‘how people across the globe use, manipulate and talk about odors in their day-to-day contexts’. Later, we show how empirical and theoretical considerations lead us to partly different conclusions. Empirically, we believe that odor naming remains poorer than naming in other senses and that careful laboratory experiments will remain critical for understanding olfactory-based language and cognition. Toward this goal, we emphasize the distinction between multisensory and unisensory olfaction, which is not highlighted in Majid's review but which we believe is of theoretical importance.

Throughout the review, Majid uses the term olfactory language to refer both to a designated, abstract odor vocabulary and an ability to name or identify odors accurately and consistently. Majid's view, it seems to us, is that cultural factors such as odor vocabularies are main drivers of odor naming success. This view is contrasted with other accounts where odors are considered more difficult to name than other stimuli because of odor-specific cortical interactions with the language system; such processes are believed to prevent efficient verbalization or the formation of abstract categories [4]. Majid provides evidence that some cultures have more refined and abstract smell vocabularies than do speakers of Indo-European languages. But is there also evidence of a widespread ability to name odors as proficiently as other sensory impressions?

In a cross-cultural study, Majid and colleagues [5] investigated how stimuli in six different senses were described verbally across 20 different cultures around the globe. Results showed that smells were uniquely difficult to describe in a consistent way. Furthermore, olfactory language was uniquely tuned to concrete source objects, rather than abstract terms (Figure 1 ). If odor naming had been similar to other senses, cross-cultural research would presumably show that olfactory naming is, overall, similar to naming in vision and other senses. But instead, there is evidence of a global trend suggesting uniquely poor and predominantly source-based naming of odors.

Figure 1.

Sensory Naming of Odors and Five Other Sensory Materials in 20 Cultures.

(A) Mean language codability for the sensory materials (Simpson diversity score) across cultures (dots indicate culture-specific mean values). (B) Mean proportion of sensory descriptions (source-based, evaluative, and abstract) across cultures. Original data (https://github.com/seannyD/LoP_Codability_Public) and code for generating the figures (https://github.com/StephenPierzchajlo/Majid-Commentary/blob/master/Majid_Graph.md) are publicly available.

How can we reconcile the seemingly contradictory results of poor odor naming with the capacity for rich and varied odor vocabularies? By making a distinction between multisensory and unisensory olfactory language. Odor naming experiments typically remove multisensory cues, whereas a vocabulary arises from rich and meaningful multisensory experiences over long time periods. Under optimal multisensory conditions, identifying odors is often fast and easy, yet naming the same odors remains surprisingly hard. This distinction should be clearly emphasized, as Majid writes that ‘odor identification is slower’ than perceiving and expressing odor valences, but in fact the cited study measured odor naming without cues, not cued odor identification [6]. Although odor naming is difficult, source-based odor identification is faster and more accurate than odor valence responses [7,8]. Everyday odor language reflects lived experience in a multisensory environment, even though some words are odor-specific.

In understanding olfactory language, context is everything. We appreciate Majid's emphasis on the cultural context that provides some cultures with sophisticated olfactory vocabularies. We emphasize the multisensory scaffolding that we believe olfactory language is particularly dependent on. For example, when we encounter a smell in daily life, we are often in a context that helps us establish its source. Cross-modal predictive coding research will help illuminate these aspects of olfactory language and its cortical correlates [9]. Studying odor language in multisensory versus unisensory contexts requires a high degree of experimental control and thus laboratory experiments can only be complemented, not replaced, by other approaches. As interest in olfaction is increasing, Majid's review provides a guide to many of the important methodological and theoretical issues discussed in the field of olfactory language and cognition.