Like the monocular and binocular cues that provided information about depth, the auditory system uses both monaural (one-eared) and binaural (two-eared) cues to localize sound.Įach pinna interacts with incoming sound waves differently, depending on the soundâs source relative to our bodies. ![]() Localizing sound could be considered similar to the way that we perceive depth in our visual fields. The ability to locate sound in our environments is an important part of hearing. However, much higher frequency sounds can only be encoded using place cues (Shamma, 2001). At frequencies up to about 4000 Hz, it is clear that both the rate of action potentials and place contribute to our perception of pitch. In reality, both theories explain different aspects of pitch perception. Therefore, hair cells that are in the base portion would be labeled as high-pitch receptors, while those in the tip of basilar membrane would be labeled as low-pitch receptors (Shamma, 2001). More specifically, the base of the basilar membrane responds best to high frequencies and the tip of the basilar membrane responds best to low frequencies. ![]() The place theory of pitch perception suggests that different portions of the basilar membrane are sensitive to sounds of different frequencies. Because of properties related to sodium channels on the neuronal membrane that are involved in action potentials, there is a point at which a cell cannot fire any faster (Shamma, 2001). While this is a very intuitive explanation, we detect such a broad range of frequencies (20â∲0,000 Hz) that the frequency of action potentials fired by hair cells cannot account for the entire range. This would mean that a given hair cell would fire action potentials related to the frequency of the sound wave. The temporal theory of pitch perception asserts that frequency is coded by the activity level of a sensory neuron. Weâll discuss two of them here: temporal theory and place theory. Several theories have been proposed to account for pitch perception. How does the auditory system differentiate among various pitches? Low-frequency sounds are lower pitched, and high-frequency sounds are higher pitched. ![]() PITCH PERCEPTIONĭifferent frequencies of sound waves are associated with differences in our perception of the pitch of those sounds. Like the visual system, there is also evidence suggesting that information about auditory recognition and localization is processed in parallel streams (Rauschecker & Tian, 2000 Renier et al., 2009). Auditory information is shuttled to the inferior colliculus, the medial geniculate nucleus of the thalamus, and finally to the auditory cortex in the temporal lobe of the brain for processing. As hair cells become activated, they generate neural impulses that travel along the auditory nerve to the brain. The activation of hair cells is a mechanical process: the stimulation of the hair cell ultimately leads to activation of the cell. The basilar membrane is a thin strip of tissue within the cochlea. As the stapes presses into the oval window, the fluid inside the cochlea begins to move, which in turn stimulates hair cells, which are auditory receptor cells of the inner ear embedded in the basilar membrane. As the ossicles move, the stapes presses into a thin membrane of the cochlea known as the oval window. This vibration results in movement of the three ossicles. ![]() Sound waves travel along the auditory canal and strike the tympanic membrane, causing it to vibrate. The ear is divided into outer (pinna and tympanic membrane), middle (the three ossicles: malleus, incus, and stapes), and inner (cochlea and basilar membrane) divisions. The cochlea is a fluid-filled, snail-shaped structure that contains the sensory receptor cells (hair cells) of the auditory system ( Figure). The inner ear contains the semi-circular canals, which are involved in balance and movement (the vestibular sense), and the cochlea. The middle ear contains three tiny bones known as the ossicles, which are named the malleus (or hammer), incus (or anvil), and the stapes (or stirrup). The outer ear includes the pinna, which is the visible part of the ear that protrudes from our heads, the auditory canal, and the tympanic membrane, or eardrum. The ear can be separated into multiple sections.
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