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By Root 894 0

results I explained that I was quite sure that no one in the audience had ever smelled the chemical compound which I poured out, and expressed the hope that, while they might find the odor strong and peculiar, it would not be too disagreeable to anyone. In fifteen seconds most of those in the front row had raised their hands, and in forty seconds the “odor” had spread to the back of the hall, keeping a pretty regular “wave front” as it passed on. About three-fourths of the audience claimed to perceive the smell, the obstinate minority including more men than the average of the whole. More would probably have succumbed to the suggestion, but at the end of a minute I was obliged to stop the experiment, for some on the front seats were being unpleasantly affected and were about to leave the room.

Slosson’s experiment vividly demonstrated the potency of olfactory suggestion, for he was holding a cotton ball soaked in nothing but water.

The sensory expert Michael O’Mahony revisited the phenomenon in the late 1970s. During a British television documentary on taste and smell, he showed viewers an electronic device that he claimed could capture and broadcast odors using “Raman Spectroscopy.” The machine played a ten-second audio tone that viewers were told would evoke a “pleasant country smell.” They were encouraged to call in or write and describe what they smelled. Many did. They reported smelling new-mown hay, freshly cut grass, lavender, honeysuckle, and so on. O’Mahony repeated the trick on a BBC radio show using a supposedly inaudible “ultra high frequency tone”—actually no sound at all. Some listeners reported smell sensations when it was played.

While amusing, these stunts by Slosson and O’Mahony raise serious questions for scientists conducting smell studies, because they show that just expecting a smell can trigger an odor perception. Thus a purely psychological expectation might have the same consequences as a real smell. For researchers the question becomes, How can we be sure the results of an odor experiment are really due to the smell and not to expectations about the smell? What is needed is an olfactory placebo: a test condition in which people are led to believe an odor is present when in fact it is not. To truly have an effect, an odor must outperform the placebo. This was the reasoning behind a study I did with Susan Knasko, a postdoctoral fellow of mine at the Monell Center, and the late John Sabini, a psychology professor at the University of Pennsylvania. We sprayed water mist in the air and told people it had a smell. The test room was actually scent-free and remained so. People who were told the smell was unpleasant later rated the room as smelling bad. When told the smell was pleasant, they liked the smell of the room. A supposedly “neutral smell” produced intermediate results. Interestingly, physical symptoms such as headache and itchy skin were also affected by the “good smell” and “bad smell.” Our study was the first to confirm in the laboratory that the power of suggestion, by itself, could produce odorlike effects.

The psychologist Pamela Dalton and her colleagues took this result and pushed it much further: they showed that expectations alter the perception of actual odors. She had volunteers sit in a test chamber for twenty minutes while exposed to odors that were neither pleasant nor unpleasant. Some subjects were told nothing about the odor. Others were told it was a potentially harmful industrial chemical or, alternately, that is was a distilled, pure natural extract. To use the Clinton-era term for expectation management, the experimental conditions differed only in spin. By the end of the test, all three groups had higher detection thresholds—their noses had been dulled by adaptation to the real odor. However, their perception of odor intensity was spin-dependent. With positive spin or no spin at all, the odor seemed less intense as time went on; with negative spin it smelled as strong or stronger. In other words, odors we think are benign fade from awareness, while those we believe to be