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How we experience smell has more to do with us than with the odor itself

Smellosophy: What the Nose Tells the Mind

A.S. Barwich
Harvard University Press
384 pp.
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Smell is an underappreciated part of life. It affects how our food tastes, how we are feeling, and to whom we are attracted. But smell is different from other senses because the connection between a smell and its physical source is fluid. The smell of your dinner persists even after it has been consumed, for example, but your eyes do not continue to see the food after the meal is finished. Similarly, although we have little trouble perceiving individual voices in a group conversation, a spice rack does not smell like a group of distinct herbs.

In her debut book, Smellosophy: What the Nose Tells the Mind, A. S. Barwich melds a philosophical perspective with a rich history of olfactory science, tackling big questions with layers of perceptual, psychological, and neurobiological explanations. She argues that olfaction does not reflect objective reality but rather a mental construct with modest relation to the chemical objects in the world. She synthesizes disparate lines of evidence in consideration of this argument, and along the way she embeds her philosophy in a larger narrative of how our current understanding of smell evolved from earlier beliefs and expectations.

Odors are experienced within a contextual tapestry of situation and experience. Lemon scent smells “fresh” to many of us and is often added to cleaning products, for example, but would be an unwelcome note in a perfume. Perfume, meanwhile, often contains fecal tones that combine with a wearer’s natural scent to evoke an earthy intimacy. If such a scent were to be smelled in a bathroom, however, it might make one wish for a lemon-scented cleaning product.

Barwich uses such observations to argue that the affective quality of odors is thus found not in their chemical structures but inside the head and history of the perceiver. She offers rich discussions of olfactory perception, the conscious and subconscious impacts of smell on behavior and emotion, and the physical and behavioral details that determine what odors we inhale, furnishing broad insights into the psychology of olfaction.

Neuroscientists studying the olfactory brain have typically operated on the assumption that chemistry is destiny for an odor, looking for spatial and temporal patterns of neural activity that “represent” the molecular structure and concentration of odorous chemicals in the nose. Barwich argues that this is a naïve approach. The olfactory circuit, she writes, begins with a mapping of odor receptors in the nose onto the surface of the brain’s olfactory bulb. Spatial patterns of neural activity across this structure capture the chemical properties of an odor. The cerebral cortex, however, seems to abandon this information, favoring instead a complex distribution of neural connections that process smells in a manner that has little relationship to odor chemistry.

Barwich suggests that contextual clues including semantic content, cultural associations, and affective value are more essential to capturing the true experience of smell. However, the challenges of testing this hypothesis are manifold. Modern research methods permit uniquely powerful experimentation in the brains of flies and mice, but if smells mean different things to lab animals than they do to human subjects—as Barwich suggests—it may be difficult to extrapolate research findings across species. By identifying the need for a more cognitive approach to olfactory neuroscience, the book sets up the practical challenge of linking human and animal research.

Barwich’s educated prose balances visceral stimulation (in one passage, she contrasts the smell of an armpit on the subway with that of one’s lover in bed) with academic language (“smells qua smells”). It is cheeky at times, alleging, for example, that perfumery is “one of the two oldest professions,” and occasionally slips in snarky asides about Kant and his ilk. The author clearly delights in putting the reader in her shoes as she recounts stories of scientists arguing, joking, and teasing each other in conversations over a beer.

Smellosophy generally resists, and at times even disassembles, clichéd smell narratives, relying instead on close consideration of the scientific literature. In chapter 4, for example, Barwich undercuts the oft-cited “madeleine incident,” in which a childhood memory is evoked by a tea-soaked cake in Marcel Proust’s In Search of Lost Time, or Remembrance of Things Past. This example is frequently used to illustrate smell’s special ability to evoke rich, emotionally laden memories. However, there is little scientific support for this claim, she reveals, noting that Proust never actually mentions the smell of the madeleine anyway. The book also sets a high bar when it comes to biological detail but deftly guides the lay reader through the minefield of terminology and competing scientific frameworks.

About the author

The reviewer is at the Department of Psychology  and the Rutgers Center for Cognitive Science, Rutgers University, New Brunswick, NJ 08854, USA.