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The Human Ear Auditory Sensation and Perception Artificial Senses - Hearing PINNA • Also called the auricle. The visible part of the outer ear. It collects sound and directs it into the outer ear canal. EXTERNAL AUDITORY CANAL •The tube through which sound travels to the eardrum. THE MIDDLE EAR • The middle ear is a sealed, air filled cavity which gives the eardrum the ability to move easily, a property called compliance. Compliance means that the eardrum moves or vibrates easily with little effort. Compliance gives the eardrum the ability to gather sound efficiently. THE MIDDLE EAR EARDRUM •Also called the tympanic membrane. A thin membrane that vibrates when sound waves reach it. HAMMER •Also called the malleus. A tiny bone that passes vibrations from the eardrum to the anvil. ANVIL •Also called the incus. A tiny bone that passes vibrations from the hammer to the stirrup. STIRRUP • Also called the stapes. A tiny, U-shaped bone that passes vibrations from the stirrup to the cochlea. This is the smallest bone in the human body (it is 0.25 to 0.33 cm long). EUSTACHIAN TUBE • A tube that connects the middle ear to the back of the nose; it equalizes the pressure between the middle ear and the air outside. When you "pop" your ears as you change altitude (going up a mountain or in an airplane), you are equalizing the air pressure in your middle ear. THE EUSTACHIAN TUBE • The eustachian tube is a selective valve that allows air to enter behind the sealed eardrum. The eustachian tube connects the back of the nose to the middle ear. Air can pass from the back of the nose to the middle ear through the eustachian tube (see diagram above). The eustachian tube replaces the air the body absorbs from the middle ear. The eustachian tube also equalizes the pressure changes in the outside air. This is what causes the "popping" that people describe when going up or down in the mountains or an airplane. The ability to "pop" the ears is very beneficial. SEMICIRCLE CANALS • Three loops of fluid-filled tubes that are attached to the cochlea in the inner ear. They help us maintain our sense of balance. COCHLEA • A spiral-shaped, fluid-filled inner ear structure; it is lined with cilia (tiny hairs) that move when vibrated and cause an electrical nerve impulse to form. VESTIBULAR COCHLEAR NERVE •Carries electrochemical signals from the inner ear (the cochlea) to the brain. HEARING/AUDITION • The brain’s ability to receive sound waves from the outside world • Sound waves are the rhythmic vibrations of air molecules LOUDNESS • The intensity/energy of a sound wave, measured in decibels. • On a graph, “amplitude” is the height of a sound wave. The higher the wave, the more force it will hit the eardrum with, and the resulting sound is louder. The lower the wave, the less force it will hit the eardrum with, and the resulting sound is softer. • Min = 0 decibels Max = 120 decibels PITCH • Pitch is the property of sound that we perceive as higher and lower tones. Changes in pitch are caused by differences in the frequency at which a sound wave vibrates. • On a graph, the more waves per second results in a higher tone, and the less waves per second results in a lower tone. • Pitch is measured in Hertz (Hz) – how many times a wave repeats per second • Min = 20 Max = 20,000 TIMBRE • The distinctive quality of individual sounds. • Created by an infinite combination of high and low frequencies (pitch), and high and low amplitudes (loudness). Hearing: Sound Localization Localization of Sound • Locating where sound is originating from • Done through two cues: –Which ear hears the sound first? –Which ear hears the louder sound? Localization of Sound Problems with hearing • Conduction deafness (middle ear damage) • Nerve deafness (hair cell or auditory nerve damage)