Presentation by Maliha Khan and Kevin Kemelmakher Hearing Presentation by Maliha Khan and Kevin Kemelmakher

Audition Audition- The sense or act of hearing.Our audition is highly adaptive allowing us to hear a wide range of sounds. The sounds we hear best have frequencies in a range corresponding to the human voice. We can also easily detect differences among thousands of human voices

Sound Waves Sound waves are compressing and expanding air molecules that vary in shapes. The amplitude of sound waves determines their loudness while the frequency determines the pitch. Frequency: The number of complete wavelengths that pass a point in a given time. Pitch: A tone’s experienced highness or lowness; depends on frequency Long waves have low frequency and low pitch while short waves have high frequency and high pitch. Sound is measured in decibels and 0 is the absolute threshold for hearing.

Sound Waves (continued)

The Ear Middle Ear- the chamber between the eardrum and cochlea containing three tiny bones (hammer, anvil, and stirrup) that concentrate the vibrations of the eardrum on the cochlea’s oval window Cochlea- a coiled, bony, fluid-filled tube in the inner ear; sound waves traveling through the cochlear fluid trigger nerve impulses. Inner Ear- the innermost part of the ear , containing the cochlea, semicircular canals, and vestibular sacs.

How we transform sound waves into nerve impulses Sound waves travel into the auditory canal until they reach the eardrum and causes it to vibrate. The eardrum passes the vibrations through the middle ear bones (hammer, anvil, and stirrup) where they are amplified and relayed through the oval window into the fluid filled cochlea. The resulting pressure changes in the cochlear membrane cause the basilar membrane to ripple, bending the hairs on the surface. These movements trigger impulses at the base of nerve cells, which are sent up the auditory nerve to the brain.

Deafness Sensorineural hearing loss (nerve deafness)- hearing loss caused by damage to the cochlea’s hair cell receptors or their associated nerves. Conducting hearing loss- hearing loss caused by damage to the mechanical system to that conducts sound waves to the cochlea. Although diseases can causes hearing loss, biological changes linked with heredity, aging, and prolonged exposure to loud music or noise are the main causes of hearing loss.

Restoring Hearing Cochlear Implant-a device for converting sounds into electrical signals and stimulating the auditory nerve through electrodes threaded into the cochlea. This allows to restore the hearing of those with nerve deafness but not of those whose brains never learned to process sound during childhood. This also triggers awakening of the pertinent brain area of human infants.

Perceiving Loudness Our brain is able to determine how loud a stimulus is based on the number of hair cells activated by a sound wave. If few hair cells are activated then the brain detects a soft sound. If many hair cells are activated the brain perceives the sound as loud.

Perceiving Pitch Place Theory- in hearing, the theory that links the pitch we hear with the place where the cochlea’s membrane is stimulated. George von Bekesy (1957) looked at the cochleas of guinea pigs and human cadavers under a microscope after cutting holes into them. He discovered that the cochlea vibrated and high frequencies produced large vibrations near the beginning of the of cochlea’s membrane while low frequencies produce vibrations at the end of the membrane.

Perceiving Pitch (continued) Frequency theory- in hearing, the theory that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense a pitch. Problem: an individual neuron can fire faster than 1000 times/sec so how can we sense sound frequencies above 1000 waves/sec? Volley Principle- combination of place theory and frequency theory. It’s the combination of place and frequency that handles the pitches in the intermediate range.

Locating Sounds Our two ears allows us to have stereophonic hearing aka 3-D hearing Sound waves strikes one ear sooner and more intensely than the other.

Can you trust your ears? Hearing Test : https://www.youtube.com/watch?v=h5l4Rt4Ol7M Cool hearing Illusions : https://www.youtube.com/watch?v=kzo45hWXRWU

McGurk Effect This phenomenon shows how we automatically integrate what we see into what we hear. The illusion occurs when the auditory component of one sound is paired with the visual component of another sound, leading to the perception of a third sound. Seeing the way a person speaks can change the way we hear the sound. People are more likely to experience the McGurk Effect when they are getting poor auditory info and better quality visual information.

The role of the brain in the McGurk effect Both the right and the left hemispheres are responsible for this effect. It is more common in right handed individuals who use their right hemisphere to analyze the face and their left hemisphere to interpret the word and speak. People who have damage to the left hemisphere of the brain rely heavily on the right hemisphere for visuals to understand what is going on. Therefore those people would have a greater McGurk effect.