What the Nose Knows - Avery Gilbert [41]
In contrast, an amateur sniffer holds the blotter in front of his nose and inhales continuously, a sure-fire way to dull the nose. Even one minute of such deep breathing makes an odor immediately harder to detect. When I run a consumer smell test, I let the panelists sniff at their own natural pace. I’ve found they can easily assess a couple of dozen scents without a noticeable decline in performance. That’s because they are sampling a variety of scents and doing so to make a quick thumbs-up or thumbs-down opinion—the typical objective of consumer and market research. This poses much less risk of adaptation than does the perfumer’s repeated study of minor differences between related samples. The average person making rapid-fire judgments does not need to worry about the smellscape fading from view.
THE LONGER YOU are exposed to an odor, the more you adapt to it. Step into a garlic factory and the reek will overwhelm you. A few minutes later its intensity fades, and after an hour you might not be able to smell garlic at all, no matter how hard you try. Work there a few months and this adjustment will happen almost as soon as you step in the door. That was how I once became oblivious to Safari. Early in my career, the company I worked for was developing the perfume for Ralph Lauren. As we tweaked the formula, ran stability tests, corrected the color, and did the million other chores needed to ensure a successful launch, the entire building was steeped in Safari. A few weeks into the job, none of us noticed it.
After a long vacation, I opened my closet to grab a suit for work, and got an overpowering faceful of Safari. The sensory truce between my nose and my workplace had fallen apart in less than two weeks. Similarly, long-term adaptation is what keeps plumbers and pig farmers from going insane.
Adaptation is a two-way street: when the odor source is removed, the nose gradually regains its sensitivity. This time-course of recovery is almost the mirror image of adaptation. Step outside after your visit to the garlic factory, and the recovery begins. If you were inside for just a few minutes, recovery will take a matter of minutes. If you were there for hours, it will be hours before full response returns. Odor strength is another factor in adaptation. The stronger the smell, the more you adapt. Ten minutes on the processing floor of the garlic factory will cause more adaptation than ten minutes talking to someone with garlic breath.
Adaptation is also odor-specific. If you work in a garlic factory, your nose will selectively tune out garlic, but your sensitivity to roses, sour milk, beer nuts, and other un-garlic-like smells will be unaffected. The narrowness of adaptation is sometimes exploited by perfumers when they try to match one fragrance to another. A perfumer will use saturation sniffing as the final step in comparing the target and the make. He sniffs the sample to the point of total adaptation, then smells the target; with his brain filtering out any sign of the original, any remaining minor differences will stand out.
Adaptation is a useful feature of any sensory system; it preserves our ability to detect small differences between stimuli against enormous variation in overall intensity. Just as auditory adaptation lets us have a whispered conversation but also talk in the middle of a rock concert, olfactory adaptation constantly recalibrates our noses to background conditions. It also selectively tunes new smells into the background, freeing our attention for the next new scent that may be creeping our way.
The Spin Doctors
In a lecture hall at the University of Wyoming in 1899, a chemistry professor named Edwin E. Slosson played a prank on one of his classes. He explained that he wanted to demonstrate the diffusion of odor through the air. He poured some liquid from a bottle onto a wad of cotton, making a show of keeping it away from his nose. He started a stopwatch and told the students to raise a hand as soon as they smelled something. Here’s what he reports happened:
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