Hearing a sound and detecting its origin sparks a complex cascade of neurological processes in areas of the brain responsible for discerning sound, vision and object location. Brain regions, such as the temporal cortex, occipital cortex, posterior parietal cortex and brain stem, all play a role in the ability to hear a sound and perceive its location, according to the National Center for Biotechnology Information.
Hearing
Sound travels into the ear and stimulates small hair cells within the cochlea, a snail-shaped structure, deep within the inner ear. Vibration of the hair cells trigger electrical impulses to travel along the cochlear nerve to the brain stem, a region located underneath the two brain hemispheres. From the brain stem, the electrical impulses travel to the auditory cortex, located in the temporal lobe, a region of the brain just above the ear. The auditory cortex allows us to hear; however, the auditory association area just above, distinguishes the type of sound, according to Kandel, Schwartz and Jessel in “Principles of Neural Science."
Sound Location
As detailed by the University of Washington psychology department, when electrical impulses from the inner ear reach the brain stem, specialized regions of the brain stem analyze the intensity of the sound and compare the time the sound requires to reach both ears. These two pieces of information provide a good estimation of sound location.
Seeing Sound Location
Processing sound location stimulates a region of the brain stem called the superior colliculus, triggering the movement of the eyes toward the sound location, according to the University of Washington psychology department. The calculation of sound location is an estimate; therefore, initial eye movement may not successfully see the location of a sound, so corrections will be required for precise localization if the sound is made by an object to be viewed.
Seeing Object of Sound
To view the source of a sound--for example, a bird--visual input will initially stimulate the receptor cells of the eyes, triggering electrical impulses to travel along the optic nerve to the visual cortex located in the occipital cortex, an area of the brain at the back of the head. This area detects the shape and color of objects and sends this information to the posterior parietal cortex, or PPC, at the top of the head, in addition to the temporal cortex, just above the ear. The PPC calculates the location of the object and the temporal cortex calculates exactly what the object is, according to Kandel, Schwartz and Jessel, in “Principles of Neural Science."
References
- National Center for Biotechnology Information: The auditory cortex
- "Principles of Neural Science"; Eric Kandel, James Schwartz and Thomas Jessell; 2000
- University of Washington, Department of Psychology: Sound Localization And Temporal Pattern Analysis
