Molecular Structure Predicts Pleasantness of Odor

The molecular structure of a substance can be used to predict how we will perceive its odor.

A new study investigated the physical laws that underlie our perception of smell. The study appeared in the September 2007 issue of the Journal of Neuroscience.

To identify the general principles by which our sense of smell is organized, Prof. Noam Sobol and colleagues at the Weizmann Institute of Science (Rehovot, Israel) and the University of California, Berkeley (Berkeley, CA, USA) used a database of 160 different odors that had been ranked by 150 perfume and smell experts according to a set of 146 characteristics (i.e., sweetish, smoky, musty). These data were then examined by a statistical program that analyzed the variance in perception among the smell experts. The scientists found that the data fell along an axis that describes the "pleasantness rating” of the odors--running from "sweet” and "flowery” at one end to "rancid” and "sickening” at the other. The same distribution along this axis closely followed the variation in chemical and physical properties from one substance to another. From this, the scientists were able to build a model to predict, from the molecular structure of a substance, how pleasing its smell would be perceived.

To double check their model, Prof. Sobel and his team tested how experimental subjects assessed 50 odors they had never smelled before for pleasantness. They found that the ratings of their test subjects fit closely with the ranking shown by their model. In other words, they were able to predict the level of pleasantness quite well, even for unfamiliar smells. They noted that, although preferences for smells are commonly supposed to be culturally learned, the responses of American subjects, Jewish Israelis, and Muslim-Arab Israelis all fit the model's predictions to the same extent.

Prof. Sobel commented, "Our findings show that the way we perceive smells is at least partially hard-wired in the brain. Although there is a certain amount of flexibility, and our life experience certainly influences our perception of smell, a large part of our sense of whether an odor is pleasant or unpleasant is due to a real order in the physical world. Thus, we can now use chemistry to predict the perception of the smells of new substances.”


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Weizmann Institute of Science
University of California, Berkeley