Olfaction Metal Oxide Semiconductor Gas Sensors and Neural Networks

Primitive mobile life forms, and the mobile cells of higher animals, derive their motivation and direct their navigation by chemical senses. In the simplest cases these creatures are hard-wired to swim toward nutrient concentration gradients, and to swim against irritant concentration gradients. The vestiges in humans of the sometimes extremely sensitive, selective, and differential chemical senses of primitive forms are taste, our ability to detect and identify four classes of chemicals in water solution on our tongues, and smell or olfaction, our ability to detect and identify many gases, vapors, and complex mixtures in the air passing through our noses.