Many experts, such as Jerry Fodor, write that the purpose of perception is knowledge, but evolutionary psychologists hold that its primary purpose is to guide action. For example, they say, depth perception seems to have evolved not to help us know the distances to other objects but rather to help us move around in space. Evolutionary psychologists say that animals from fiddler crabs to humans use eyesight for collision avoidance, suggesting that vision is basically for directing action, not providing knowledge.
Building and maintaining sense organs is metabolically expensive, so these organs evolve only when they improve an organism’s fitness. More than half the brain is devoted to processing sensory information, and the brain itself consumes roughly one-fourth of one’s metabolic resources, so the senses must provide exceptional benefits to fitness. Perception accurately mirrors the world; animals get useful, accurate information through their senses.
Scientists who study perception and sensation have long understood the human senses as adaptations. Depth perception consists of processing over half a dozen visual cues, each of which is based on a regularity of the physical world. Vision evolved to respond to the narrow range of electromagnetic energy that is plentiful and that does not pass through objects. Sound waves go around corners and interact with obstacles, creating a complex pattern that includes useful information about the sources of and distances to objects. Larger animals naturally make lower-pitched sounds as a consequence of their size. The range over which an animal hears, on the other hand, is determined by adaptation. Homing pigeons, for example, can hear very low-pitched sound (infrasound) that carries great distances, even though most smaller animals detect higher-pitched sounds. Taste and smell respond to chemicals in the environment that are thought to have been significant for fitness in the EEA. For example, salt and sugar were apparently both valuable to our ancestors, and we are favor salty and sweet tastes. The sense of touch is actually many senses, including pressure, heat, cold, tickle, and pain. Pain, while unpleasant, is adaptive. An important adaptation for senses is range shifting, by which the organism becomes temporarily more or less sensitive to sensation. For example, one’s eyes automatically adjust to dim or bright ambient light. Sensory abilities of different organisms often coevolve, as is the case with the hearing of echolocating bats and that of the moths that have evolved to respond to the sounds that the bats make.
Evolutionary psychologists claim that perception demonstrates the principle of modularity, with specialized mechanisms handling particular perception tasks. For example, people with damage to a particular part of the brain suffer from the specific defect of not being able to recognize faces (prospagnosia). EP suggests that this indicates a so-called face-reading module.