Localization of Irritations

Localization of irritations

The localization of stimuli, as well as the ability to distinguish between their various qualities, depends on specific connections between the sensory organ and the brain. The child learns very early that two sensations, identical in quality, can be associated with irritations coming from different sides of the body. He is able to localize a bright light in the left eye or pain from an injection in the right side simply because in the brain the endings of the nerve pathways from the left eye and right side and from the right eye and left side lie in different places.

It is more difficult to localize odors and even more difficult to localize sounds, since the stimuli that cause them are more general in nature and distributed more diffusely. The importance of the brain in the occurrence of sensations is clearly evident in the sometimes observed phenomenon of “referred pain.” A well-known example is the experience of people who suffer from heart disease, but complain of pain in the right shoulder. In reality, of course, the stimulus originates in the heart, but for some as yet unclear reason, the corresponding nerve impulse arrives in the same part of the brain as the impulses that actually originate in the shoulder, chest, or arm.

Unlike the quality and localization of the stimulus, which depend to such a large extent on the places of arrival of the impulses in the brain, the intensity of the sensation depends almost entirely on the sense organ sending the impulse.

With almost all sensations, not one, but many impulses are sent along the nerve fiber, and it is their number that determines the strength of the sensation. A hard slap produces more impulses per second than a light slap, and the larger the area hit, the stronger the sensation, as more receptors will be affected and more impulses will be sent to the brain.