Place Theory of Hearing: Definition & Explanation
What Is the Place Theory of Hearing?
The place theory of hearing is used to explain how we distinguish high-pitched sounds that possess a frequency that exceeds 5,000 hertz. According to the place theory of hearing, we can hear different pitches due to specific sound frequencies causing vibrations in specific parts on the basilar membrane of the cochlea. In other words, different parts of the cochlea are activated by different frequencies.
Each location on the basilar membrane possesses a particular characteristic frequency. For example, a sound that measures 6,000 hertz would stimulate the spot along the basilar membrane that possesses a characteristic frequency of 6,000 hertz. The brain detects the pitch based on the position of the hair cells that transmitted the neural signal.
Structure of the Ear
In order for us to truly understand the place theory of hearing, we must first have basic knowledge about the structure of the ear. This picture depicts the different parts of the human ear.
We absorb sound into the outer ear, which includes the external auditory canal and the auricle, or pinna. The sound transforms into an acoustical signal after it is absorbed. The tympanic membrane, commonly known as the eardrum, is the part of the ear that separates the outer ear from the middle ear.
Once the acoustical signal has reached the middle ear, the motion of the ossicular chain, which is made of the malleus, incus, and stapes, causes the acoustical signal to become mechanical. The ossicular chain also carries the acoustical signal to the inner ear, the location where the sound enters the cochlea. This image contains the various structures of the cochlea. It also demonstrates how sounds of varying frequencies can activate specific areas of the cochlea.
Housed within the cochlea is the the Organ of Corti, also known as the hearing organ, which houses sensory hair cells. Once the sound enters the cochlea, it causes the hair cells of the Organ of Corti to move. The sound is then converted into nerve impulses that are carried to the brain through the auditory nerve.
The major assumptions of the place theory of hearing are that the hair cells respond independently at different locations and that specific sound frequencies cause specific hair cells to vibrate. Low frequencies activate the hair cells and auditory nerve fibers that are near the narrow tip of the cochlea, while high frequencies activate the areas that are closest to the cochlea’s opening. The frequency of a tone is therefore determined in part by the place along the basilar membrane of the cochlea that is firing the most frequently.
Frequency Theory and Place Theory
Place theory of hearing is unable to account for sounds with very low frequencies, such as those in bass notes, due to the fact that there are no auditory nerve fibers that have a preference for very low frequencies. But how then do we hear these sounds? This can be explained by the frequency theory of hearing. According to the frequency theory, the frequency of the nerve impulses of the auditory nerve corresponds to the frequency of a tone, which allows us to detect its pitch. The entire basilar membrane is activated by sound waves at different rates. As a result, the neural impulses are transmitted at different rates.
The frequency theory of hearing generally accounts for sounds with a frequency of 1,000 hertz or less. Sounds between 1,000 and 5,000 hertz are processed using a combination of the frequency theory and place theory. Anything above 5,000 hertz is explained by the place theory.
Let’s review. The place theory of hearing states that different parts of the cochlea are activated by different frequencies. Sound is absorbed into the outer ear as an acoustical signal and is later converted into nerve impulses that are carried to the brain.
The major assumptions of the place theory of hearing are that the hair cells respond independently at different locations and that specific sound frequencies cause specific hair cells to vibrate.
The place theory of hearing can only account for higher frequencies. The frequency theory of hearing accounts for low frequencies.