Chapter Overview

Sensation refers to the ability of the sense organs to receive messages from the outside world, while perception refers to the ability to organize and interpret these messages.

We receive external stimuli through specialized sensory receptor cells. First, sense organs receive stimuli. Next, they transduce this sensory energy into neural impulses. The neural impulses are then sent to the brain to be interpreted. The field that studies the relationships between physical stimuli and psychological sensations is called psychophysics.

The sense of sight functions by detecting light energy. The intensity of a light wave determines its brightness, while the wavelength largely determines color. The eye, which works much like a camera, is the primary sense organ for seeing. Light enters the eye through the cornea and lens and then enters the retina. Rods and cones transduce light waves into neural impulses for transportation to the brain. The 100 million rods are located throughout the retina but are not found in the fovea. Although they are active in peripheral vision and vision in dim light, they do not play a role in color vision. The 6 million cones, clustered mainly near the fovea, are involved in color vision. Two theories that explain color vision are trichromatic theory and opponent-process theory.

The sense of hearing functions by detecting sound waves. The frequency of sound waves determines pitch, while their intensity determines loudness. The outer ear collects sound waves, which vibrate the eardrum. The eardrum is connected to a series of movable bones in the middle ear. The inner ear, which contains the cochlea and the organ of Corti, transduces the sound waves' energy into neural impulses. These impulses are transported to the brain.

The sensory system also receives information about internal stimuli. For example, the vestibular organ provides information about body orientation, and the kinesthetic sense reports bodily position and movement. The various skin senses can detect pressure, temperature, and pain.

Humans also possess chemical senses, such as taste and smell. These senses respond to chemicals in the environment rather than to energy.

The interpretation of sensory neural impulses that have been transmitted to the brain is called perception. Perception is an active mental process. Gestalt principles explain many of the ways in which humans tend to organize sensory information. Individual factors, such as motivation and prior learning, also affect perception.