What the Nose Knows - Avery Gilbert [39]
SO CLOSELY IS sniffing tied to odor perception that people routinely sniff when they are asked to imagine a smell. Without prompting, they take larger sniffs when imagining pleasant odors and smaller ones when imagining malodors. During visual imagery the eyes explore an imagined scene using the same scan paths made when viewing the actual visual scene. Preventing eye movements during visual imagery—by having people stare at a stationary target—reduces the quality of the image. Sobel found that, similarly, imagined odors were more vivid when people could sniff than when they were wearing nose clips and unable to sniff. Actually sniffing increased the unpleasantness of an imagined bad smell (urine) and increased the pleasantness of a good one (flowers). Sniffing at an imaginary odor isn’t an absentminded habit—it’s a behavior that improves the mental image we are trying to create. Sobel’s claim that “the sniff is part of the percept” would have outraged Charles Elsberg, but it sounds reasonable to most neuroscientists today.
We have in fact done a complete about-face since Elsberg’s attempt to measure smell without sniffing. Because smelling is sniffing, we can now test odor perception by measuring sniffing alone. We can take advantage of the fact that people naturally and unconsciously take smaller sniffs when an odor is present: the stronger the odor, the smaller the sniff. People with no sense of smell fail to adjust; they keep inhaling as if the air were unscented. A new smell test, developed by University of Cincinnati psychologists Bob Frank and Bob Gesteland, is simplicity itself. The patient wears a pair of standard-issue medical nose tubes connected to an electronic console, and sniffs at half a dozen cylinders in a row. That’s it—test over. No need to identify smells by name, no multiple-choice questions, no rating scales, no fancy odor generators. Here’s how it works: Each cylinder is the size of a can of beans and may or may not contain a slightly unpleasant odor (in pilot testing, Frank and Gesteland used methylthiobutryate, which has the character of feces, putridity, decay). The test console records airflow into the patient’s nose and computes the size of each sniff. It compares sniffs made when the patient was smelling scented cylinders with those made to an empty cylinder. If the two types of sniff are of similar size, the patient almost certainly has an impaired sense of smell.
Remedial Sniffing
We have glasses to help those with defective vision, hearing aids for the partly deaf, and who now will produce an artificial device to improve the smelling ability of people with subnormal noses?
—Popular Science Monthly, 1931
If perception and sniffing are inseparable, what happens to people who can’t sniff? The most extreme case of nonsniffing is the person with a total laryngectomy, or removal of the voice box (larynx), a procedure that disconnects the upper and lower respiratory airways. After laryngectomy, a person breathes through a hole in his throat, rather than through the mouth or nose, so he is unable to sniff or even activate his vocal cords to speak. Adding to their misery, about 85 percent of these patients are smell-impaired. Fortunately, some can be helped by a simple physical maneuver that resembles a polite yawn, or in other words, yawning with the mouth closed. This pseudo-sniff technique pulls air through the nose (though not the lungs) and allows about 50 percent of patients to score in the normal range on a smell test. A device called a tracheostomy valve, which directs exhaled air upward past the vocal cords and into the back of the nasal passages, restores speech function and also improves odor perception.
Impaired sniffing also occurs in Parkinson’s disease and contributes to the smell loss found in these patients. Because the disease affects motor movement, the sniffs of a Parkinson