How sound and smell can create perfect harmony

Sound and vision are not the only senses that work together – new studies show that even sound and smell can form an unlikely pairing

What does that scent sound like? New research is helping to redefine our understanding of the senses. Photomontage: The Guardian/Getty Images

A few years ago, on work experience at Oxford University's psychologydepartment, I found myself roped in to participate in an experiment by a research team led by Professor Charles Spence. Sitting in a tiny room in the warren of labs and offices, I was shown a rack of bottles of scent and a simple computer program that let me play the sound of musical instruments at different pitches. My task was to sniff each of the scents, and pick the sound that fitted best with each smell.

Puzzled, I inhaled my first sample – sweet and slightly sickly, like bubble gum. Deep blaring brass seemed instinctively wrong, so I tried out higher and purer sounds and eventually settled on a high piano note. An hour later, I left not much the wiser about what was going on. Only later did I find out that the team was covering new ground in a field known as crossmodal perception.

When we think about how our senses work, we imagine them operating individually: you sniff a flower, and the smell is delivered uninterrupted from nose to brain. However, it is more complicated than that. Our senses mingle more often than we realise, collaborating to help us make sense of the world more easily. For example, we call dull thuds "heavy" and associate them with large objects, even though the sound itself has no size or weight. This would have helped our ancestors decide whether to run away from predators based on how big they sounded, without stopping to look them over. Most evidence for crossmodal perception comes from studies into sound and vision, which isn't surprising considering how often we use them together. But research that shows other senses crossing over is emerging all the time, and it seems that even sound and smell sometimes form an unlikely pairing.

Two New York researchers, Daniel Wesson and Donald Wilson, were confronted with this fact when they began investigating an "enigmatic" area of the brain known as the olfactory tubercle. Originally, they only intended to measure how olfactory tubercle cells in mice responded to smell. But during testing, Wesson noticed that every time he clunked his coffee mug down next to the experiment, the mouse cells jumped in activity. In fact, the olfactory tubercle is physiologically well-placed to receive both smell and sound information from the outside world; and so Wesson and Wilson broadened their investigation.

They found that among individual cells, most responded to odour but a significant number were also active when a tone was played. Some cells even behaved differently when smell and sound were presented together, by either increasing or suppressing their activity. As Wesson and Wilson point out, there may be some evolutionary sense behind the phenomenon – the sound of movement accompanied by an unfamiliar smell could alert you to the presence of a predator.

Of course, mice are not people, and a handful of firing cells don't always add up to a conscious experience. But Charles Spence and Anne-Sylvie Crisinel have been carrying out experiments such as the one in which I participated at Oxford University, which seem to show that sounds and smells cross over in human perception, too. Recently, they delved into the world of wine-tasting, using a kit designed to help novices learn about the basic smells found in wine. Participants in their experiment were asked to sniff different samples, and then match them to an appropriate musical instrument and pitch. There were interesting consistencies in the smells people picked. Piano was often paired with fruity scents and with smells that participants said were less complex. Musky and unpleasant smells, meanwhile, sounded like brass.

Further research found that listening to different sounds can alter your perceptions. Studying taste this time, the team ordered some cinder toffee made by Heston Blumenthal's Fat Duck restaurant and put together "soundscapes" corresponding to bitterness and sweetness. Participants tasted identical pieces of toffee while listening to each soundscape, and found the toffee more bitter or sweeter, depending on which soundtrack they were listening to.

Studies like this are helping psychologists redefine our understanding of the senses, and how the brain integrates them to its advantage. And just imagine the possible creative collaborations between musicians andchefs: sound-enhanced wining and dining could be imminent. You might one day be routinely ordering a coffee with a soundtrack to bring out your favourite aromas. Best not to mention all this to Starbucks.

• This article is a winner of the Wellcome Trust Science Writing Prize2012.