THE FIVE SENSES, AND BEYOND
the constant sampling of water by certain fish whose skin is covered by taste buds. Many animal species use pheromones, substances that transmit information from one creature to another by odor. Smell and taste do not play similarly important roles for humans, so these senses might seem like mere frills for artificial beings.
Nevertheless, artificial smell is important for uses such as detect- ing contaminants in air or water and can take on additional meaning because the sense of smell is linked to the fabric of thought. The human olfactory system has complex neural pathways, some going to the limbic system of the brain.This is a collection of interacting parts that appeared early in the evolution of the mammalian brain and is strongly tied to instincts and feelings. Odors can be powerfully evoca- tive because they speak directly to this ancient core.This might seem irrelevant to machine thought, which we tend to characterize as ra- tional rather than emotional. But a variety of evidence shows that reason and emotion are connected in our own brains and minds, as I will discuss in Chapter 8. True artificial thought might also require both and might be enriched by a layer of nonrational but valid mean- ing entering the brain through the sense of smell.
For now, though, artificial taste and smell are at an early stage where sensors are still being developed. This is also partly true for touch. However, we already have digital hardware that can detect and manipulate light, and sense and produce sound. Progress in artificial hearing, speech, and vision focuses on the cognitive abilities that sup- port these three vital functions.
SEEING INTO KNOWING
Creating synthetic vision as powerful as the natural version is not easy, partly because the human eye is a remarkable optical instrument, with high resolution, the ability to distinguish millions of colors, and a variable focal length. But these features are enormously enhanced by the mind. Under mental control (largely at an unconscious level) your eyes automatically refocus to provide clear vision from near to far, and they constantly move, to ensure that the portion of the retina with the highest resolution points at the most significant part of a scene.