Perception is a creation of the brain that goes beyond the input of sense organs. Sense organs detect changes in the environment, and transmit the information as nerve impulses or action potentials. Sensory neurons carry the action potentials to the brain. The name, sensation, is given to an action potential traveling from a sense organs to the brain. Sensations from different sense organs travel to different parts of the brain. When sensations reach their brain centers, the brain interprets them and produces a perception. In this way, we perceive the difference between sight and sound. Using memory, we also make perceptual inferences about the world around us. For example, when we see a moving car consistently getting larger, we determine that it is coming toward us. By means of a complex process, the brain extracts features such as color, motion, and orientation from sensations in order to create a perception.
The path from stimulus to perception begins with a sense organ. Sense organs contain sensory receptors, structures that detect shifts in the environment both outside and inside the body. Cells in sensory receptors respond to specific stimuli, such as heat, light, pressure and chemicals. Five functions occur along the path to perception: reception, transduction, amplification, transmission, and integration. During reception, a receptor cell absorbs energy from a stimulus. Absorption occurs in a specialized area of the cell.
For example, sensory cells in the eye absorb light in special pigments in their cell membranes. During transduction, receptor cells transfer the energy from an incoming stimulus to an action potential. The stimulus changes the membrane potential of the receptor cell thereby initiating an action potential. Amplification strengthens the signal that will be carried to the brain. In the ear, a particular structure performs this function. Percussion waves in the air cause the tympanic membrane to vibrate with the same frequency as the waves in the air. Then the three bones of the middle ear amplify the sound wave twenty times before it reaches the sensory receptors in the inner ear. Initiating an action potential leads to transmission. Some receptors are sensory neurons that transmit the impulse to the central nervous system themselves, while others transmit the impulse across a synapse to a sensory neuron. The final step, integration, is the processing of information by the brain when sensory impulses arrive. One type of integration, sensory adaptation, decreases responsiveness. Because of sensory adaptation, people do not feel the clothing that they are wearing or hear the sound of their hearts.
Scientists are studying perception from different perspectives. One line of research attempts looks at disordered perception so as to understand the normal function. Some researchers are examining an abnormal condition known as synesthesia in which the senses intermingle. Some people suffering with this disorder see colors when they hear certain sounds. For example, patients with synesthesia may hear U as yellow and O as white. Studies show that the disorder is accompanied by unusual brain activity, and may be inherited.
This is the complete article, containing 495 words
(approx. 2 pages at 300 words per page).
