EAR REVIEW

MODULE 20 – HEARING Describe the characteristics of air pressure waves, and explain the process by which the ear transforms sound energy into neural impulses. Discuss the theories that help us understand pitch perception. Describe how we locate sounds.

SOUND CHARACTERISTICS Sound is continuous changes that occur in the pressure of air, water, or other substances. Such changes cause sound waves to be produced. Sound waves have certain properties. 1) Loudness: depends on the amplitude (height), or intensity, of each sound wave. Amplitude is shown by the height of the wave and is measured in decibels. 2) Pitch: refers to the highness or lowness of sound, which is determined by the frequency. Frequency is the number of complete waves that pass through a medium every second. Hertz is the measurement of frequency. 3) Timber: refers to the purity of the sound wave. Most sound waves are not comprised of a single frequency, but of many different frequencies. Timber is determined by the complexity or multiplicity, of the different frequencies.

OUTER EAR – collects and channels sound waves Pinna: the visible out part of the ear; locates the sound wave. Auditory Canal: channels the sound wave to the eardrum. Eardrum: a membrane that vibrates in response to incoming sound waves (eardrum vibrations match frequency of sound wave).

MIDDLE EAR - amplifies sound onto the oval window, which separates the middle ear from the inner ear. Made up of three tiny bones: hammer, anvil, and stirrup. Each bone causes the next bone to vibrate, resulting in increased amplitude.

INNER EAR – vibrations from the oval window cause the fluid in the cochlea to move, causing basilar membrane vibrations, which cause the hair cells to move. Transduction takes place as the hair cells move back and forth, causing cells in the auditory nerve to become stimulated. The auditory nerve then carries the message to the thalamus, which then sends it to the auditory cortex. Cochlea: fluid-filled tube, resembles a snail Basilar Membrane: lines the cochlea and contains hair cells (also called cilla), the sensory receptors for audition. Auditory Nerve: carries the message to the thalamus, which then sends it to the auditory cortex.

THE EAR

HEARING LOSS 1) Conduction Hearing Loss: occurs when either the eardrum is punctured or there is damage to any of the three tiny bones located in the middle ear. Can be overcome with the use of a hearing aide. 2) Sensorineural Hearing Loss: (nerve deafness) occurs when there is damage to the hair cells located in the inner ear or auditory nerve. May be overcome by a cochlea implant which is a device for converting sounds into electrical signals and stimulating the auditory nerve through electrodes threaded into the cochlea.

Discuss the theories that help us understand pitch perception. The basilar membrane is the key structure responsible for distinguishing pitch, which is determined by frequency. The frequency-matching and place theories explain how people are able to discriminate among different pitches. Both theories are correct in explaining the perception of pitch. The Frequency theory accounts for low frequencies and the Place theory is used to explain high frequencies.

Discuss the theories that help us understand pitch perception. 1) Frequency-Matching Theory: (Volley Principle) the vibrations of the basilar membrane are determined by the frequency of the vibrations. A high frequency will cause large vibrations on the basilar membrane, whereas a low frequency causes small vibrations. The vibrations on the basilar membrane affect the hair cells, generating a neural message to travel via the auditory nerve to the brain. The greater the vibrations and the more movement among the hair cells, the faster the message will travel up the auditory nerve. However, neurons can only fire about a thousand times per second; this makes it hard for the frequency theory to account for frequencies that cause neurons to fire faster than their capabilities. Therefore, the frequency theory can only account for low frequencies.

Discuss the theories that help us understand pitch perception. 2) Place Theory: suggests pitch depends on where vibrations stimulate the basilar membrane. Higher frequencies trigger hair cells on one end of the basilar membrane, which causes a certain pitch, whereas lower frequencies trigger hair cells on the opposite end, causing a different pitch.

Describe how we locate sounds. Stereophonic Hearing: because we have two ears, sounds that reach one ear faster than the other ear causes us to localize the sound. Your right ear would receive a more intense sound from this bell ringing, and it would receive the sound slightly sooner than your left ear. However, the intensity difference and time lag are extremely small.