Unit 2

noise pollution

a result of our modern industrial society

noise

either any vibration lacking the “regularity” that characterizes music sounds or any unwanted or annoying sound

environment

conditioning by or expectations of the ____ play a role in determining responses to sound

background noise

any noise must be perceptible above _____ to be annoying- often with unique spectra, periodicities, and impulsive natures

emotionally involved

a person who has been ____ with a sound will be more sensitive to it

factors that influence reaction to sound

moods/emotional factors, whether or not the noise is essential, presence of visual information, frequency of occurrence, predictability

recruitment

results from a raised threshold of hearing at low levels and a normal threshold of hearing at high levels

dBA scale

gives an approximate indication of the loudness of a sound by attenuating the low and very high frequencies in a manner similar to the ear

noise climate

SPL band where the majority of the noise exists

continuous equivalent level (LeqdBA)

dBA level averaged over time to yield an equivalent dBA level of steady sound that would provide the same total sound energy in the same time

noise pollution level scale

adds a measure of the fluctuation in SPL in an attempt to refine the Leq scale

day-night average level

an additional 10dB is added to the night levels to compensate for greater annoyance potential at night

50-60 dB

day-night levels desirable for quiet residential neighborhoods

noy

unit of noise

perceived noise levels (PNdB)

noys converted into decibels become; take into account the information content of a noise and the subjective responses to this noise by humans

noise and number index (NNI)

take into account not only the level of noise, but the number of aircraft flying overheard during a certain time period

effective perceived noise level (EPNdB)

takes into account maximum loudness and duration

noise exposure forecast (NEF)

accounts for number of events

negative effects of noise

damage hearing, interfere with warning signals, interfere with speech, distract from the task at hand, cause annoyance

masking effect

will often help provide a measure of privacy without expensive sound insulation

Leq=30 dBA, Lmax=45dBA

levels ideal for undisturbed sleep

irregular noise

causes more changes of sleep state than monotonically increasing noise levels

physiological responses to noise

increased heart rate, increased blood pressure, modified hormone secretion, lengthened recuperation time from medical treatment

psychological responses to noise

general stress, annoyance leading to anxiety, sleep loss, depression, mental disorders, interference with a person’s attention

infrasound

produces undesirable effects even at imperceptible levels

economic costs of noise

lost time on the job, hearing-loss lawsuits, medical expense, devaluation of real property

Noise Control Act of 1972

deals with noise emission standards for products distributed commercially as well as noise standards for aircraft, railroads, and motor carriers

residential areas

should be kept separated from industrial areas, airports, railroads, and freeways

commercial zones

can be used as buffer zones between residential and industrial zones

conductive loss

hearing loss occurring because of problems in the outer or middle ear- results in a reduced conduction (transmission) of sound to the sensing elements of the ear

sensorineural loss

hearing loss occurring because of problems of the inner ear or neural pathway- caused by a partial or complete breakdown of the nerve-sensing elements of the ear

pure tone audiometer

a device used to test hearing acuity- threshold of hearing can be established and compared with a standard threshold curve

audiogram

a graph showing hearing level at different frequencies

causes of conductive hearing loss

blockage of the ear canal: buildup of waxy secretions, infection in the canal, inflammation. A perforated eardrum: sticking objects into the ear, receiving a sharp blow to the side of the head, getting an infection. Inflammation of the middle ear: infections transmitted through the eustachian tube into the middle ear. Dislocation in the bone chain

otitis media

middle ear

tinnitus

“ringing in the ears"- ringing, rushing, or roaring noises in the ear that come and go spontaneously without any sound stimulus

Meniere’s disease

caused by an excess pressure in the cochlear fluid of the inner ear

most serious hearing impairment

loss of or damage to the hair cells in the cochlea

presbycusis

affects people as they get older- gradually become insensitive to high-frequency sounds

low-level sounds

loss of outer hair cells leaves the ear less-sensitive to

hearing aid

any instrument that provides amplified sound to the ear

electronic hearing aid

consists of a microphone which converts sound into electrical energy, an amplifier, and an earphone (receiver) to convert the electrical signal back into sound

binaural aid

may enable its user to localize, face, and concentrate on a talker, thus reducing the effect of competing sounds

cochlear implant

consists of as many as 20 or more electrodes inserted through the round window and surgically implanted in and along the cochlea

temporary threshold shift (TTS)

temporary hearing loss leads to a temporary upward shift of our threshold of hearing

permanent threshold shift (PTS)

studies show a positive correlation between TTS acquired on a regular basis and this

occupational noise exposure

principal cause of hearing loss

ways of effecting noise protection

1) attenuating the noise before it enters the human ear

2) stopping the noise at the recipient’s ear

basic types of hearing protectors

muff protectors word over the ear and insert protectors worn in the ear

dosimeters

devices that can measure time-averaged sound levels

Occupational Safety and Health Act (OSHA) of 1970

federal law which includes attempts to limit worker exposure to intense sounds

outer-ear stage

incoming sound is converted to mechanical motions of the eardrum

middle-ear stage

mechanical motion undergoes an amplification process as it is transmitted to the entrance of the inner ear

inner-ear stage

the mechanical motion sets up wave motions in the cochlea, which in turn stimulates the hair cells. Neural pulses from the hair cells are transmitted to the brain

infrasonic

inaudible low frequency sounds

ultrasonic

inaudible high frequency sounds

outer ear

consists of the pinna, auditory meatus, and the tympanic membrane- protects the middle and inner ear mechanisms from harsh external environments and helps maintain internal temperature and humidity

pinna

visible portion of the ear- serves a limited function in filtering sounds and in the localization of high-frequency sounds

auditory meatus

ear canal

tympanic membrane

eardrum

middle ear

consists of a small chamber containing three tiny bones which transmit vibrations from the eardrum to the inner ear

inner ear

complex cavity filled with a fluid and the structures necessary to convert mechanical vibrations to neural pulses

concha

bowl-shaped part of the pinna leading into the ear canal

compound resonant system

concha and the ear canal form a

eustachian canal

connects middle-ear cavity to the throat, normally closed- thus sealing the middle-ear cavity and maintaining the middle ear pressure independent of the external air pressure

auditory ossicles

three small bones of the middle ear- the malleus (hammer), incus (anvil), and stapes (stirrup). Transmit the vibrations of the eardrum to the fluid of the inner ear, amplify the pressure from the outer ear (causes the fluid of the inner ear to vibrate appreciably)

oval window

membrane covered entrance to the cochlea

pressure

this at the oval window is 22x as great as that at the eardrum

ossicular structure

provides limited protection to the inner ear from high sound levels

semicircular canals

detect angular acceleration in three dimensions, interact with eyes to allow visual fixation on a point during head movements

cochlea

a transducer shaped like a snail’s shell which transforms mechanical vibrations into neural pulses

scala vestibuli

upper duct of the cochlea

scala tympani

lower duct of the cochlea

scala media

extends along almost the entire length of the cochlea from its basal end at the oval window to its apical end where it terminates at the helicotrema

helicotrema

opening between the upper duct and the lower duct which provides a path for fluid flow between the two

round window

a flexible membrane where scala tympani joins the middle ear

vibratory motions at the oval window

set up pressure waves in the upper fluid-filled duct of the cochlea

pressure difference

the _____ between the upper duct and the lower duct sets up traveling waves in the basilar membrane

high frequencies

where the basilar membrane is stiff (near oval window), it responds to more

low frequencies

where the basilar membrane is flexible (near helicotrema), it responds to more

organ of Corti

where conversion of the wave motion in the basilar membrane into electrical pulses is accomplished, contains thousands of hair cells that are attached to the nerve transmission lines going to the brain

cilia

“hairy ends” of the hair cells that are close to and possibly embedded in the tectorial membrane

shearing motion

when the basilar membrane vibrates up and down, the tectorial membrane and the BM move crossways relative to each other in a____, thus stimulating the hair cells

inner hair cells

the primary sensory cells

outer hair cells (OHC)

primarily serve an amplification function

OHC contractions

cause a “pump action” of the fluid in the organ of Corti- resulting in an amplification of the basilar membrane motion

frequency

can be thought of as being partially encoded in terms of the place along the basilar membrane that responds most strongly

characteristic frequency

a single auditory neuron has a _______ to which it responds most strongly in the discharge of pulses per second

time

frequency information is also encoded in ____ as the repetition rate or periodicity of hair cell discharges

neural pulses

encoding of a sound wave’s intensity is determined by the number of ______ produced in each burst

basilar membrane

more intense sounds cause a greater portion of the _____ to vibrate

frequency

when two signals lying close to each other in ______ stimulate the membrane, the regions of stimulation will overlap and there will be interaction- competition for the same hair cells

critical band

a frequency range within which two sinusoids interact significantly- varies with frequency

masking

the drowning out or covering up of one sound by another

observations on masking

1) tones closer together in frequency mask each other more than tones widely separated

2) low-frequency tones mask high-frequency tones more effectively than vice versa

3) greater the intensity of the masking tone, broader the band of frequencies for which masking is evident

2 and 4 kHz

average human ear is most sensitive to frequencies between

loudness

corresponding perceptual quality to sound level

pitch

corresponding perceptual quality to frequency

tone color

corresponding perceptual quality to spectrum

threshold of audibility

frequency-dependent sound level at which sound is just audible, determined at different frequencies