Olfactory discrimination: the Nose Knows.

One TRILLION different smells?  Seems impossible to test and less likely prove, but then note that COMBINATIONS of base smells were used.  This is a little like generating lots of different shapes and colors and combinations of the same, and calculating the different color plates one could make.  By that measure, vision discrimination would be much, much higher.

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Science 21 March 2014: 
Vol. 343 no. 6177 pp. 1370-1372 
DOI: 10.1126/science.1249168

• REPORT

Humans Can Discriminate More than 1 Trillion Olfactory Stimuli

1. C. Bushdid1,*, 
2. M. O. Magnasco2, 
3. L. B. Vosshall1,3, 
4. A. Keller1,†

• ABSTRACT

Humans can discriminate several million different colors and almost half a million different tones, but the number of discriminable olfactory stimuli remains unknown. The lay and scientific literature typically claims that humans can discriminate 10,000 odors, but this number has never been empirically validated. We determined the resolution of the human sense of smell by testing the capacity of humans to discriminate odor mixtures with varying numbers of shared components. On the basis of the results of psychophysical testing, we calculated that humans can discriminate at least 1 trillion olfactory stimuli. This is far more than previous estimates of distinguishable olfactory stimuli. It demonstrates that the human olfactory system, with its hundreds of different olfactory receptors, far outperforms the other senses in the number of physically different stimuli it can discriminate.

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