Sound Perception

n Sound – mech disturbances produce vibrations – more dense, faster moving

q Room temp 340 m/sec, water 1500 m/sec, wire 5000 m/sec

q Slightly faster when warm

n Pitch – size of wavelength – high pitch, short wavelength – hertz (cycles/sec) 20-20,000 hz

n Loudness – amplitude, decibels (20 log p1/p0), threshold at 0, damage at 85 db, pain at 125 db, decreases with distance

Sound

n Timbre – complexity of wave, music – what makes 2 sounds different if hold freq, amp, duration, and rate of decrease constant

n Phase difference – compression and expansion of wave, in and out of phase

Outer Ear

n Pinna – helps funnel sound into ear, sound localization

n Auditory canal – 3 cm, protect eardrum, resonance (enhance intensity of certain sounds – 2,000-5,000 hz)

n Tympanic membrane – eardrum, vibrates to sound waves

Middle Ear

n Malleus, incus, stapes

n Impedance mismatching device – air to fluid, w/o 3% vibrations transmitted

q Larger bone to smaller

q Hinged (like fulcrum)

n Eustachian tube – to throat, keep air pressure in middle ear same as outside

n Acoustic reflex – middle ear muscles connected to bones to restrict movement

Conductive hearing loss

n Problems with sound making it to cochlea

n Outer ear – too much ear wax, something in ear, “swimmer’s ear”, rupture of tympanic membrane

n Middle ear – otitis media, eustachian tube blocked, tissue build-up from infections, Otosclerosis – bone growth

Inner Ear

n Cochlea

n Oval window, round window

n Vestibular canal (Reissner’s membrane), Cochlear partition (basilar membrane), tympanic canal

n Organ of Corti – receptors are located, under tectorial membrane

Sensorineural Hearing loss

n Presbycusis – old age – higher pitch, environment

n Noise induced – acoustic trauma

n Tinnitus

n Meniere’s disease – buildup of fluid

Receptors

n Outer

n 12,000-20,000

n 3 rows

n Embedded in membrane

n Cylindrical in shape

n Cilia - V shaped, 150, flexible

n 10% neural connections

n sensitivity

n Inner

n 3500

n 1 row

n Free floating

n Flask shaped

n Cilia – stiff, 40

n 90% neural connections

n Details

Outer Hair Cells

n Afferent pathway – from ear to brain

q 32,000 fibers

n Efferent pathway – brain to ear

q Involves outer hair cells and efferent pathway – outer hair cell cilia flexible (motile resp), serve to amplify traveling wave and enhance very fine discrimination

n Otoacoustic emissions – ear produces noise, about 40% of pop., 1K-2K hz, less than 20 db – damage to system from noise (feedback)