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Hearing

Also known as Audition

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Sound waves are composed of compression and expansion of air molecules.

The Stimulus Input: Sound Waves

Acoustical transduction: Conversion of sound waves into neural impulses in the hairs cells of the inner ear. 2

1. Frequency (pitch)2. Intensity (loudness)

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Sound Characteristics

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1. Stimulus = sound waves (vibrations of molecules traveling in air)

2. The amplitude refers to the height and subsequent intensity of the sound wave.

3. Loudness refers to the perception of the sound wave4.Wavelength (pitch)

-measured in cycles per second (Hz)

Hearing: The Auditory System

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5. Frequency refers to the number of compressions per second and is measured in hertz.High frequency = high pitch 6. Sound pressure – decibels

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Prolonged exposure above 85dbhearing loss

Frequency (pitch): Dimension of frequency determined by wavelength of sound.

Wavelength: The distance from the peak of one wave to the peak of the next.

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Frequency (Pitch)

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Intensity (Loudness): Amount of energy in a wave determined by amplitude relates to perceived loudness.

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Intensity (Loudness)

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Anatomy of the EarAnatomy of the Ear The ear is divided into three major areas

Outer (external) ear

Middle ear

Inner (internal) ear

The Ear

1. The outer ear includes the pinna and is responsible for:Altering the reflection of sound waves into

the middle ear from the outer ear.Helping to locate the source of a sound.

2. The middle ear contains the tympanic membrane which vibrates when struck by sound waves.Three tiny bones (malleus, incus, & stapes)

also hammer, anvil, stirrup (ossicles)transmit information to the oval window

Parts of the Inner Ear Parts of the Inner Ear Cochlea

Oval window

Semicircular canals

Basilar membrane

1. inner ear contains a snail shaped structure called the cochlea which contains fluid

2. hair cells are auditory receptors that excite the cells of the auditory nerve when

moved by vibrations in the fluid of the cochlea.

3. lie between the basilar membrane and the cochlea.

CochleaCoiled, bony, fluid-filled tube in the inner ear that transduces sound vibrations to auditory signals.

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Vibrating airossiclesfluid waveselectrical impulses to the brain!

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Pitch perception explained in two theories

Place Theory suggests that sound frequencies stimulate basilar membrane at specific places resulting in perceived pitch.

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Frequency Theory states that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch.

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Theories of Audition

SoundFrequency

Auditory NerveAction Potentials

100 Hz200 Hz

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The current pitch theory combines modified versions of both the place theory and frequency theory:Low frequency sounds best explained

by the frequency theory.High frequency sounds best explained

by place theory.

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Volley principle states that the auditory nerve can have volleys of impulses (up to 4000 per second) even though no individual axon approaches that frequency by itself. provides justification for both theories

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About 99% of hearing impaired people have at least some response to loud noises.

Two categories of hearing impairment include:

1. Conductive or middle ear deafness.

2. Nerve deafness.

Conductive deafness occurs if bones of the middle ear fail to transmit sound waves properly to the cochlea.

Caused by disease, infectionsCan be corrected by surgery or hearing aids

that amplify the stimulus.

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Sensorineural deafness results from damage to the cochlea, the hair cells or the auditory nerve.

Can be confined to one part of the cochlea.people can hear only certain frequencies.

Can be inherited or caused by prenatal problems or early childhood disorders (rubella, syphilis, inadequate oxygen to the brain during birth, repeated exposure to loud noises, etc). 15

Tinnitus is a frequent or constant ringing in the ears.experienced by many people with nerve

deafness.Sometimes occurs after damage to the

cochlea.Similar to the mechanisms of phantom limb.

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Cochlear implants are electronic devices that enable the brain to hear sounds.

Deaf Culture

Cochlear ImplantDeaf Musician 17

Other Important Senses

Module 15

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Other Important Senses

Touch

Taste

Smell

Body Position and Movement

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Sense of touch is a mix of four distinct skin senses- pressure, warmth, cold, and pain.

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Only pressure has identifiable receptors, all other skin sensations are variations of pressures, warmth, cold and pain.

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Skin Senses

Burning hot

Pressure Vibration Vibration

Cold, warmth and pain 16

Pain tells the body that something has gone wrong. Usually pain results from damage to the skin and other tissues. There is a rare disease in which the person feels no pain.

Pain

Ashley Blocker (right) feels neither painnor extreme hot or cold.

Congenital Insensitivity to Pain with Anhidrosis, or CIPA

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Pain depends on several types of axons, several neurotransmitters, and several brain areas.

Mild pain triggers the release of glutamate while stronger pain triggers the release of glutamate and substance P.Substance P results in increased intensity of

pain. Morphine and opiates block pain by blocking

these neurotransmitters.

Gate-Control Theory

Melzak and Wall (1965, 1983) proposed that our spinal cord contains neurological “gates” that either block pain or allow it to be sensed.

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Taste (gustation)Physical stimulus: soluble chemical substances Receptor cells found in taste buds

Pathway: taste buds neural impulse thalamus cortex Taste: learned and social processes

The Chemical Senses: Taste

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Taste

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Traditionally taste sensations consisted of sweet, salty, sour and bitter tastes. Recently receptors for a fifth taste have been discovered called “Umami”.

Sweet Sour Salty Bitter Umami(Fresh

Chicken)

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The Sense of TasteThe Sense of Taste Taste receptors

Taste buds (Widely scattered throughout the oral cavity)

Location of taste buds Most are on the

tongue

Soft palate

Inner surface of the cheeks

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Sensory Interaction

• When one sense affects another sense sensory interaction takes place.

• So the taste of strawberry interacts with its smell and its texture on the tongue to produce flavor.

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Smell

Like taste smell is a chemical sense. Odorants enter the nasal cavity to stimulate 5 millions receptors to sense smell. Unlike taste there are many different forms of smells.

Smell and MemoriesBrain region (red) for smell is closely connected with brain regions (limbic system) involved with memory, that is why strong memories are made through the sense of smell.

Body Position and Movement• The sense of our body parts’ position

and movement is called kinesthesis. • vestibular sense monitors the head (and

body’s) position.

Whirling Dervishes Wire Walk