The temporal theory of pitch perception asserts that frequency is coded by the activity level of a sensory neuron and that the firing rate of cilia or groups of cilia encode constant pitch perception. We’ll briefly discuss three of them here: temporal theory, volley theory and place theory.

Several theories have been proposed to account for pitch perception. B,C and D show the cochlea unraveled and illustrate how high, medium and low frequencies propagate respectively across the basilar membrane (adapted from Encyclopedia Britannica, 1997). A shows activation that occurs at each frequency. Low-frequency sounds are perceived as lower pitch due to activation of cilia deep in the cochlea, whereas high-frequency sounds are higher pitched and processed closer to the base of the cochlea. When hair bundles are stimulated, the stereocilia are sheared towards the tallest row of stereocilia, this is also defined as the positive direction of stimulation (from Pang, Salles, Pan & Ricci, 2011).ĭifferent frequencies of sound waves are associated with differences in activation of cilia along different areas of the basilar membrane.

salient features of stereocilia rows that comprise the hair bundle are indicated.

(c) enlargment of a schematic of the hair bundle and hair cell apical surface seen in a. iHc and oHc hair bundles are pseudo-coloured orange and red, respectively. (b) scanning electron microscopy image looking at the apical surface of hair cells with the tectorial membrane removed. Hair bundles on the apical surface of inner hair cells (iHcs) and outer hair cells (oHcs) are bathed in endolymph, whereas the basolateral side of hair cells is bathed in perilymph. (a) cross-section of the organ of corti pointing out the salient features relevant to hearing transduction. 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 transmitted via the auditory nerve to the inferior colliculus (upper sections of the brainstem), the medial geniculate nucleus of the thalamus, and finally to the auditory cortex in the temporal lobe of the brain for processing. The activation of cilia is a mechanical process in that stimulation of the hair cell occurs when the hair cell is bent in response to a frequency of signal from structures of the middle ear causing a chemical reaction that triggers electrical action potentials for further processing of the auditory information in the brain. The basilar membrane is a thin strip of tissue within the cochlea that houses the cilia which allow the component pieces of the sound to be broken down into different frequencies. As the stapes presses into the oval window, the fluid inside the cochlea begins to move, which in turn stimulates hair cells known as cilia, 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 below). 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. It will include a discussion of how the sensory stimulus is translated into neural impulses, where in the brain that information is processed, how we perceive pitch, and how we know where sound is coming from. This section will provide an overview of the basic anatomy and function of the auditory system. This sensations of vibration allows us to hear the sounds of nature, appreciate the beauty of music, and to communicate with one another through spoken language. Our auditory system converts pressure waves into meaningful units of sound.

Explain how we encode and perceive pitch.

Describe the basic anatomy and function of the auditory system.

By the end of this section, you will be able to:

Auditory nerve definition psychology