Chapters 13, 14, and 15
Chapters 13, 14, and 15 1230.0
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Date Created: 12/11/15
Chapter 13 14 and 15 Hearing Science Disorders and Rehabilitation Hearing is the sense of perceiving sound The physical bases include measurements of Frequency Intensity Phase The Psychological or perceptual measures are Pitch Loudness Timbre To be a sound source an object must have mass and elasticity The more elastic the object the more likely it will be a good sound source A waveform is the graph that represents the passage of time showing when the vibrations start and stop Shows all characteristics of a simple sound to be quantified The four quantities that are considered Frequency Duration Amplitude Starting phase Frequency is the number of cycles of vibration that occur in 1 second Amplitude is the measure of distance of how far away from the resting position the soundwave moves Duration is how long the sound lasts Starting phase describes the position of the sound source when the vibration begins The four quantities characterize simple sounds which is a sound that vibrates at a single frequency Complex sounds are vibrations that contain two or more frequencies Rather than using waveforms complex sounds use spectrum to depict them The process of sound propagation is when air molecules closest to the sound source vibrate and bounce off of the surrounding air molecules sending the sound energy in all directions Vertebrates such as mammals are the only animals that have an auditory system per se The auditory system consists of two parts the ear the outer middle and inner ear and the auditory nervous system neural pathways associated nuclei and the brain Consists of the pinna and external auditory meatus EAM Pinna is the visible ap of skin attached to the head The pinna funnels outside sounds into the EAM EMA is a tube that is closed off at one end by the eardrum The Pinna and EAM have the capacity to selectively boost or amplify sounds The tympanic membrane or eardrum forms the boundary between the outer and middle ear Attached to the TM is the malleus which is connected to the incus which is connected to the stapes These three bones are known as the ossicular chain and are the smallest bones in a human At the oor of the middleear cavity is a passageway that connects the middle ear to the back of the throat The passageway is call the Eustachian Tube The ossicles provide a pathway for sound to travel from the outer ear to the inner ear An important role of the middle ear is overcoming the impedance mismatch between the air and uid in the middle ear Like the middle ear the inner ear resides in a hollowed out portion of the temporal bone The inner ear consists of a series of inter connected cavities known as the bony or osseous labyrinth The osseous labyrinth is divided into three distinct areas The cochlea Vestibule Semicircular canals The cochlea is a coiled tube that houses the membranous labyrinth and basilar membrane The basilar membrane is a thin ribbon of tissue One edge is attached to a lip of bone called the osseous spiral lamina The other edge is supported by the spiral ligament The basilar membrane is stiff at one end and loose at the other so it doesn t move in unison This pattern is called the traveling wave The cochlea performs another function that is essential to hearing it converts mechanical energy to electrical energy The process of converting that energy is called transduction and is accomplished by hair cells Which rest of the basilar membrane The bottom of the hair cells are rooted in the basilar membrane While their tips are embedded in the tectorial membrane Sound is now in an electrochemical form that can be interpreted by the brain Information is transmitted from the cochlea by the auditory nerve through the brainstem then the midbrain and finally to the auditory cortex The eighth nerve Which consists of approximately 30000 neurons carries the electrochemical impulses through this channel Information is not transmitted directly to the brain by the eighth nerve Parallel neural pathways run on both sides of the head The impact that hearing loss has on daily life is in uenced by the age of onset severity of the loss and other factors specific to the individual For infants and young children the loss can interfere with typical development of speech language and social skills However hearing loss is not always present at birth Adults can acquire hearing loss at any age Hearing loss varies in configuration and severity from person to person Difficulties can leas individuals with hearing loss to withdraw from activities in their normal lives Audiologist receive specialized training in graduate school to learn how to perform and interpret the tests used to diagnose hearing loss The type of hearing loss is determined by identifying which part or parts of the ear are involved A rudimentary knowledge of the anatomy and physiology of the ear is needed to recognize how the different tests contribute to defining the type of loss Sound travels through the air as a series of waves with their respective compressions and refractions Those sounds reaching the head are gathered by the pinna and carried down the EAM to the tympanic membrane The cochlea acts as a microphone to convert mechanical energy into electrical energy that is then sent to the brain People do not hear with their ears but with their brains the ear is just a means of enabling hearing Sound energy could also reach the inner ear by vibrating the bones of the skull with bone conduction to bypass the conductive mechanism Hearing levels are measured with an audiometer The audiometer uses st to introduce the concept of hearing level Whereas SPL soundpressure level has a specific intensity reference HL refers to the intensity necessary to evoke a threshold response from persons with normal hearing Any threshold greater that 15 dB HL is considered to demonstrate a hearing loss by air conduction bone conduction or both Puretone air and bone conduction testing is performed for each ear individually using an audiometer to determine hearing thresholds at different frequencies measured in Hertz The frequencies that are generated are usually available at octave intervals aver a wide frequency range This type of testing is completed in a soundtreated booth and is a behavioral test Behavioral hearing thresholds can typically be obtained at approximately 6 months of age Air conduction thresholds provide information about the degree of hearing loss When they are obtained in conjunction with bone conduction thresholds the type of hearing loss can be determined Hearing sensitivity is displayed on an audiogram Audiograms are inverted meaning larger numbers are near the bottom and lower are near the top Audiologists plot where the horizontal and vertical axes intersect to show the patient s threshold for each frequency for each ear by both types of conduction Right ear is in red and shown using a circle Left ear is in blue and shown using an X Sound can crossover to the other ear when hearing is not symmetrical and when bone conduction testing is being performed Hearing loss not only results in difficulty hearing certain sounds because of reduced audibility but also can affect the clarity of sounds The speech recognition threshold SRT assesses how intense speech must be to be audible The word recognition score WRS assesses how well speech can be discriminated when loud enough to be heard STRs are customarily measured using twosyllable words called spondees where both syllables are uttered with the same stress Most clinicians measure WRS using lists of 50 oneword syllable phonetically balanced words so called because they contain all the phonemes of the language with their approximate frequencies in connected discourse WRSs are measured in percentages rather than in st People with normal hearing usually have very high WRSs People with conductive hearing loss usually have high WRSs Sensorineural hearing loss has some measurable distortion Usually the greater the sensorineural hearing loss the poorer the WRSs The tests just described need cooperation from the patient and are called subjunctive tests Immittance a combination of impedance and admittance because no system is totally efficient in sound transmittance American National Standards Institute The measurement of the mobility of the tympanic membrane and middleear system is call tympanometry As the air pressure is varied above and below normal atmospheric pressure the tympanic membrane becomes stiffer by being pulled gently into the middle ear and pulled out into the external auditory canal Tympanometry can reveal such conditions as tympanic membrane perforation interruption in the ossicular chain uid in the middle ear or stiffness of the ossicles Whenever a sound is heard it is recognized as changes in electrical activity by a number of relay sites along the auditory path in the brain These early responses are called the auditory brainstem response ABR Used for testing infants from birth to 6 months determining the site of lesion in the auditory pathway and measuring hearing in noncooperative patients The inner ear produces some very faint sounds These sounds have been called spontaneous otoacoustic emissions OAE and are present in about half of all individuals with the normal hearing OEAs are used for screening the hearing of infants and young children They are present when the cochlea is functioning normally and there is no blockage in the outer or middle ear space Hearing status is generally classified as being normal or showing one of three types of hearing loss conductive sensorineural or mixed People with normal hearing sensitivity show auditory thresholds below 15 dB HL at all frequencies Individuals with conductive hearing losses show impairment by air conduction But they have normal conduction by bone The problem most likely resides in the outer in middle ear Degree of hearing loss will vary for air conduction based on the cause and extent of the problem Bone conduction will always remain within the normal range Damage to the outer or middle ear Loss or damage to pinna does not really affect hearing but the collapsing of the EAM will cause problems Otitis media is the primary cause of hearing loss in the middle ear The inner ear is responsible for the body s balance and equilibrium in addition to its role in hearing Damage to the cochlea produces sensoryneural hearing loss May range from very mild sometimes showing virtually normal hearing for low frequencies and depressed hearing for higher frequencies to profound or total hearing loss The thresholds for boneconducted tones and airconducted tones are about the same The degree of speech discrimination difficulty is often linked directly to the degree of hearing loss Usually involves damage to the cochlea or the auditory nerve May occur pre peri or postnatally Prenatal can be inherited or cause by prenatal complications Perinatal are typically caused by some type of birth complication Postnatal are often caused secondary to prolonged otitis media or other infections or even the aging process Could also result from damage or irritation to the auditory nerve that are usually unilateral Most common is acoustic neuroma or a tumor that forms on the vestibular branch of the auditory nerve Usually causes tinnitus and is either rapidly or slowly progressing from mild to total hearing loss Combination of both conductive and sensorineural The amount of Sensorineural is expressed as the difference between 0 dB HL and the bone conduction threshold at each frequency The amount of Conductive is the difference between the bone conduction threshold and the air conduction threshold at each frequency As the Sensorineural component increases the bone conduction threshold becomes higher or lower on the audiogram and as the Conductive component becomes greater the ABG increases Audiologic habilitation services are provided to children who are learning speech and language skills for the first time Audiologic rehabilitation services are provided for adults who need to modify their communication style as a result of an acquired hearing loss The type of hearing devices indicated for individuals with hearing loss depends on a variety of factors Traditional air conduction hearing aids bone conduction hearing aids cochlear implants and assistive listening devices are all options They have 4 basic components Microphone Amplifier Receiver Battery The microphone convert acoustic signals into electrical signals These signals are then passed to the amplifier which increases the amplitude however not all frequencies are amplified the same amount The amplified electrical signals are then sent to the receiver where they are converted back to acoustic signals that are more intense than the original input Advancements in hearing aid technology have led to greater availability to wireless connections to help individuals hear signals from other electronical devices They are available in many different styles and the size has become smaller over time Recommendations for style options take into account the degree and configuration of the hearing loss in addition to patient preferences Some styles are BTE or Behindtheear MiniBTE ITE or intheear CIC or completely intheear RITE or receiverintheear Bone conduction hearing aids are used for individuals with significant conductive losses They consist of a microphone amplifier battery and bone oscillator The bone oscillator replaces the air conduction receiver and is usually placed behind the pinna and can be surgically implanted or held onto the mastoid by a band They can malfunction for many reasons and need to be checked daily It is critical that the hearing aid battery has sufficient voltage to power the aid Only the earmold can be cleaned with water and only after it is removed from the aid If it necessary for the hearing aid to be sent out for repair the audiologist may be able to provide a loaner hearing aid For individuals with severe to profound sensoryneural hearing losses traditional hearing air amplification provides limited or no benefit because of damage within the cochlea There are eligibility guidelines for cochlear implantation imposed by the FDA The implant consists of a microphone a signal processor a transmitter a receiver and an electrode array The signal processor analyzes the input signal and determines how to stimulate the cochlea The transmitter device is held in place by a magnetic force between it and the receiving device that was surgically placed under the skin The main goal of amplification is to increase the auditability of the speech signal Individuals with hearing loss often have difficulty hearing and understanding speech in the presence of background noise and reverberation Reverberations are the sound re ections from hard surfaces Children with hearing losses should be placed in classrooms that have reverberation times no greater than 04 seconds Listening environments can be described in terms of signaltonoise ratio SNR which is the signal intensity minus the noise intensity The more positive the SNR the better the listening situation To improve SNR assistive listening devices ALDs can be used to reduce the levels of background noise and reverberation One such ALD is an FM system For these a teacher wears a microphone that is attached to an FM transmitter The transmitter acts as a mini radio and broadcasts the FM signal to an FM receiver worn by a student Another way to transmit signals is by electromagnetic fields They can be generated by telephone handsets a hearing aid in the telecoil can pick up these signals These ALDs require that the individual with a hearing loss have a receiving device or hearing aid to pick up the signals These devices help individuals to hear important sounds such as fire alarms a baby s cry a telephone or an alarm clock These devices have the ability to increase the intensity of a signal or alter its frequency range so that it is in the listener s audible range Another way to alert someone who has difficulty hearing is to use ashing lights or vibrotactile stimulation In terms of habilitation and rehabilitation wearing the technology and aids is only part of the process The language centers of the brain must be able to make sense of the information received It may be tempting to equate hearing loss and the use of hearing technology with vison loss and the use of correction lenses This is typically not the case with hearing aids and is hardly ever the case with cochlear implants The first few years of a child s life are particularly important in establishing a strong foundation of neurological growth It is critical for hearing losses to be identified as quickly as possible so that hearing technology can be placed before too much developmental time is lost Many children with hearing loss use American Sign Language ASL for communication and may or may not ever utilize hearing technology Children are now screened for hearing loss as newborns There are three levels to the listening development hierarchy Detection Discrimination Identification Detection is the ability to identify when a sound is present versus when it is not present Discrimination is the ability to process the auditory differences between the sounds being heard Identification occurs after the child has learned and comprehends a symbolic representation for the sound Audiological treatments and therapies also include the complex tones in music in order to practice perceiving and comprehending the sounds Most individuals with no hearing aids or spoken language resort to ASL It is not possible to sign ASL simultaneously with spoken English because there are significant differences between grammars Is provided to individuals who need to modify their communication style because of lateonset or acquired hearing loss With hearing loss some portions or even all of a speech message may not be audible and therefore not understood This can cause miscommunications 10 11 Because this type of hearing loss is usually progressive and typically progresses slowly individuals might not recognize that they are experiencing hearing loss and not memory loss Paranoia or social isolation can also develop from these miscommunications Sometimes a great deal of encouragement is required before an individual Will try hearing aids