Audibility & linear hearing instrumentsPresentation Transcript
AUDIBILITY & LINEAR HEARING INSTRUMENTS •Lenses for Eyes vs. HIs for EarsFitting hearing instruments for presbycusisis very different from fitting lenses forpresbyopia.The general public is well aware thateyeglasses work better for vision thanhearing instruments do for hearing.
AUDIBILITY & LINEAR HEARING INSTRUMENTS •Lenses for Eyes vs. HIs for EarsThe visually challenged consumer is alsoaware that most typical vision problemsresult from an improper focus of light onthe retina.Simply, the retina does for vision whathair cells do for hearing. (the retinachanges light into electricity—thelanguage our brains understand)
AUDIBILITY & LINEAR HEARING INSTRUMENTS •Lenses for Eyes vs. HIs for EarsThe refocusing of light on the retina withproperly fitted lenses is similar to fitting aperson with conductive hearing loss withhearing aids.
AUDIBILITY & LINEAR HEARING INSTRUMENTS •Lenses for Eyes vs. HIs for EarsFor poor vision, incoming light must beproperly focused upon the retina to beproperly conducted or refocused.For conductive hearing loss, sound mustsimply be made louder so that it can getthrough the middle ear and reach thenormal cochlea (no damaged hair cells).
AUDIBILITY & LINEAR HEARING INSTRUMENTS •Lenses for Eyes vs. HIs for EarsIf optometrists had the same job ashearing instrument specialists, they wouldmost often be seeing patients withscratched or damaged retinas. However,this is more of an exception than the rulefor that profession.
AUDIBILITY & LINEAR HEARING INSTRUMENTS •Lenses for Eyes vs. HIs for EarsFor the most part, hearing instruments arefit where the hair cells of the cochlea havebeen damaged—similar to the distortionof vision experienced through maculardegeneration.The hair cells of the cochlea are the“retina” of the ear.
AUDIBILITY & LINEAR HEARING INSTRUMENTS •Lenses for Eyes vs. HIs for EarsThe benefits of a hearing instrument arenot always as immediately obvious as thebenefits of a vision lens.If the anticipated hearing instrument(s)benefits are not clear to the patient/clientor if the hearing instrument(s) is notphysically comfortable, they will not wearthem.
AUDIBILITY & LINEAR HEARING INSTRUMENTS •Audibility and Speech in NoiseFor most people with hearing loss whowear hearing instruments, increasingaudibility is not enough and theimportance of understanding speech innoise cannot be overestimated.
AUDIBILITY & LINEAR HEARING INSTRUMENTS •Audibility and Speech in NoiseWhy do those who wear hearinginstruments bitterly complain regardingtheir ability to hear in noise?Damaged/missing hair cells result inreduced clarity and certainly manifest theirreduced numbers when attempting totransmit complex information to the brain.
AUDIBILITY & LINEAR HEARING INSTRUMENTS •Audibility and Speech in NoisePatient/clients with speech in noisechallenges must have the opportunity fora better signal-to-noise ratio.While normal hearing individuals canunderstand speech fifty percent of thetime when the speech and noise areequally loud, pathologic ears are unable todo so—the speech must be severaldecibels louder than the noise.
AUDIBILITY & LINEAR HEARING INSTRUMENTS •Audibility and Speech in NoiseResearch has found that with each onedecibel of speech to noise improvement, apathologic ear may have a ten percentbetter opportunity to understand thatspeech signal.
AUDIBILITY & LINEAR HEARING INSTRUMENTS •Audibility and Speech in NoiseThese one decibel improvements canresult into a fifty percent greateradvantage of understanding speech innoise—if the patient/client has enoughresidual hearing ability to perform.
AUDIBILITY & LINEAR HEARING INSTRUMENTS •Audibility and Speech in NoiseSince there are now digital hearinginstruments utilizing directionalmicrophones, a five to six decibel ofspeech to noise ratio can be electro-acoustically achieved.Let’s review the history of hearinginstrument technology.
AUDIBILITY & LINEAR HEARING INSTRUMENTS•Carbon microphones (developed around 1900) When coupled with early electronicamplifiers would produce more gain;however, they also produced significantamounts of distortion
AUDIBILITY & LINEAR HEARING INSTRUMENTS•Vacuum tubes (developed around 1920) Were more compact and reliable thanthe carbon era. Also, created moreamplification and less distortion.
AUDIBILITY & LINEAR HEARING INSTRUMENTS•Transistor (developed in the mid-1940s) Now, not only could hearing instrumentsbe worn on the body, they could now beworn on the head i.e. ear level. Moreamplification with even less distortionbecame a reality.
AUDIBILITY & LINEAR HEARING INSTRUMENTS•Integrated Circuits (IC) (developed 1970s) Would utilize thousands of transistors inthe design of the amplifier chipset. Was the beginning of tremendousminiaturization of hearing instruments i.e.from ear level to in-the-eartransducer/amplifier location.
AUDIBILITY & LINEAR HEARING INSTRUMENTS•Digital age (mid 1990s) The integrated circuits were miniaturizedfurther to include millions of transistors. They became “digitized” through thedevelopment of analog to digital (A/D)converters.
AUDIBILITY & LINEAR HEARING INSTRUMENTS• Body hearing aids Were found in the carbon, vacuum tube, and transistor phases of hearing instrument development
AUDIBILITY & LINEAR HEARING INSTRUMENTS•Eyeglass hearing aids (used transistors & ICs ) Were introduced to “hide” the hearingaid. Also to “hide” the wiring required for aCROS fitting.
AUDIBILITY & LINEAR HEARING INSTRUMENTS•Behind-the-ear hearing aids (use transistorsand IC) Early versions were ear level however,bigger than some ears! Today’s versions are very small anddiscreet.
AUDIBILITY & LINEAR HEARING INSTRUMENTS•In-the-ear hearing aids May be either custom or modular indesign. Have an additional acoustic advantagewith microphone placement inside of theear.
AUDIBILITY & LINEAR HEARING INSTRUMENTS•Completely-in-the-canal hearing aids Very discreet—translates into consumerappeal. Its deep insertion can create addedacoustic amplification.
AUDIBILITY & LINEAR HEARING INSTRUMENTSFitting of hearing instruments is not anexact science.Unlike a lens for vision, the “retina” of theear requires a sharpening of the travelingwave and the separation of speech fromnoise which a damaged cochlea is unableto perform.
AUDIBILITY & LINEAR HEARING INSTRUMENTS•Hearing Instrument Fitting MethodologyHearing instrument fitting formulae areused to determine how muchamplification is required to achieveaudibility for certain types of hearing loss.
AUDIBILITY & LINEAR HEARING INSTRUMENTS •Hearing Instrument Fitting MethodologyThere are two basic fitting formulae. Oneis based upon the thresholdmeasurements of hearing loss—known aslinear fitting formulae.The other is based upon the supra-threshold measurements of residualhearing ability—known as compressionfitting formulae.
AUDIBILITY & LINEAR HEARING INSTRUMENTSWe will discuss more regarding varioushearing instrument fitting formulae nextweek.