title: On the dimensionality of odor space.
abstract: There is great interest in understanding human olfactory experience from a principled and quantitative standpoint. The comparison is often made to color vision, where a solid framework with a three-dimensional perceptual space enabled a rigorous search for the underlying neural pathways, and the technological development of lifelike color display devices. A recent, highly publicized report claims that humans can discriminate at least 1 trillion odors, which exceeds by many orders of magnitude the known capabilities of color discrimination. This claim is wrong. I show that the failure lies in the mathematical method used to infer the size of odor space from a limited experimental sample. Further analysis focuses on establishing how many dimensions the perceptual odor space has. I explore the dimensionality of physical, neural, and perceptual spaces, drawing on results from bacteria to humans, and propose some experimental approaches to better estimate the number of discriminable odors.
authors.affiliation: Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, United States.
authors.forename: Markus
authors.initials: M
authors.lastname: Meister
mesh_terms: D006801:Humans; D008962:Models, Theoretical; D009812:Odorants / Q000032:analysis*; D055696:Olfactory Perception
keywords: E. coli; computation; computational biology; human; mouse; neuroscience; olfaction; perception; systems biology