If you are ambitious to found a new science, measure a smell,” said Alexander Graham Bell to a graduating class in 1914. A century later, scientists are still working on it. But it’s not just smell that remains difficult to define and categorise. Humans can calculate pi to trillions of digits, but can we agree on what the colour teal is? Or whether coriander tastes nice? Or when pleasant stroking becomes annoying tickling? The mildly unnerving point is that much of the information we learn through our senses cannot be objectively measured. Colour “doesn’t actually exist outside of our brains … there is also no sound, or taste, or smell … it’s the brain that construes them.”
“How do you describe a feeling?”, asked Kylie Minogue in 2007. In this book, Ashley Ward, the author of The Social Lives of Animals and a professor in animal behaviour at the University of Sydney, uses a rollercoaster combination of science, cultural history, romance, philosophy and schoolboy humour. “But what is beauty?” he wonders, quickly running through the views of Plato, Aristotle, David Hume and Immanuel Kant before pointing out that “men with more symmetrical features have more sex, with more people”. Whether or not you like coriander depends on which variation you have of a single gene, OR6A2. If you want to know what teal looks like you should ask a woman – they have “a greater ability to distinguish between closely matched colours” than men. The ideal rate of stroking is 3cm to 5cm a second – according to recent research using robots with paint brushes – at which our heart rate slows, our blood pressure drops and our brains release natural painkillers and opioids. And if you want to witness how our senses can influence our unconscious bias, try asking volunteers to make moral judgments about a potential out-group after dousing the research room with fart spray. The disgusting smell makes them more prejudiced, even if they don’t notice it’s there.
Ward explores one sense at a time, looking at its evolution, biology and cultural associations. He devotes an equal amount of space to each of the well-known five, but it’s clear that his sympathy lies with the underdog senses, touch, “our most profound sense”, and the ever-so-ethereal smell. Sight may be regarded as “the ultimate arbiter of truth,” he says, but “sight is the sense most prone to being tricked”.
That said, all our senses fool us, much of the time, especially when they give us conflicting information. A famous experiment by Frédéric Brochet, a PhD candidate at the University of Bordeaux, “tricked a large group of wine experts by adding red food dye to white wine”. Even sound can affect our experience of taste. “Lively, higher-pitched music tends to increase the perception of acidity, while more mellow tunes accentuate wine’s fruitiness.” Can we not trust what’s right in front of our eyes (or ears, or mouth)?
One of the messages of this book is that we should be willing to take our perceptions with a pinch of salt (which works by turning down bitter notes in food, “giving rise to a perception that other flavours are enhanced”) and accept that other people’s realities may be quite different, and equally true. It’s not so much that our senses are fooling us, rather what happens when their signals reach our complex, unique, brilliant brains. But that is cause for wonder, too. To show this, Ward enters a sensory deprivation chamber, where he experiences vivid, visual hallucinations – “the brain’s frantic efforts to build its internal model” when all external stimuli are removed. “It’s this fantasy that paradoxically provides our experience of what we call reality,” he writes. “This extraction of meaning from the jumble and chaos of physics is what makes us, us.”
• Sensational: A New Story of Our Senses by Ashley Ward is published by Profile (£20). To support the Guardian and the Observer buy a copy at guardianbookshop.com. Delivery charges may apply.