Speech Audiometry
Speech Audiometry is the process of testing the auditory ability of a patient by the use of words. There are two types of tests in this process, and they include the threshold tests that are used to attest the pure tone results and supra-threshold tests that find out the level of speech recognition that a patient can attain. Speech recognition threshold (SRT) is the widely used test where patients are assessed whether they can repeat half of the presented words in a correct way such that SRT and Pure Tone Average (PTA) correspond within 12Db (Speech Audiometry, n. d.). Spondee words that the patients repeat exactly as they hear them are tested with the SRT. The descending method of testing is applied at predetermined steps until 50% of word recognition is achieved (Speech Audiometry, n. d.). The lowest level of recognition in the process is recorded as SRT.
In SRT, the Speech awareness threshold or speech detection threshold can be used to assess children or adults who are unfamiliar with the language to detect their word responses. Masking during SRT is conducted when the difference between recorded SRT and inter-aural attenuation in the test ear exceeds the best SRT recorded in the non-test ear. The threshold is achieved when the SRT due to noise in the non-tested ear shifts below 5dB when compared with SRT in the tested ear. The Plateau method is used in case the shifts exceed the 5db. Similarly, Speech Recognition Score (SRS) is a supra-threshold speech recognition test that detects hearing loss, checks the communication function of the patient, and estimates whether hearing aids will work well for the individual.
Monosyllabic words presented at 40dB are used with carrier phrase that a patient repeat after the clinician. The test is done through recording or live voice. 2% of the words should be repeated right (Speech Audiometry, n. d.). Masking in SRS is done when the level of word presentation in the test ear exceeds the best negative score of SRS in the non-test ear. Results from SRS show that people with normal hearing perform word recognition well, retro-cochlear pathology causes poor SRS, and inconsistent SRS shows a possible retro-cochlear pathology.
Functional Hearing Loss
Functional hearing loss occurs when there are inconsistencies in the hearing ability of a person during an audiological evaluation due to exaggerated hearing thresholds. Functional hearing loss cannot be attributed to an organic cause. The prevalence of functional hearing has reduced in recent times because of improved audiologic detection and training procedures. Only 5% of children experience this hearing loss with girls more likely to be affected than boys. Aural-palpebral reflexes and behavioral signs should not be used to diagnose functional hearing loss because they result from organic hearing loss that is highly associated with false alarms. Speech threshold tests are more efficient in detecting functional hearing loss than pure-tone average tests. Stenger tests can be done to ascertain the pure tone configuration that is associated with functional hearing loss. However, functional hearing loss can be confirmed by an acoustic reflex threshold (ART) value of 10% and below. Proper counseling procedure that is devoid of intimidation and allows full participation of the patient brings about functional hearing loss’ resolution.
Pediatric Audiology and Universal Newborn Hearing Screening
Hearing loss in newborn babies should be identified by three months and resolved within six months. 0.2% 0r 0.3% of American children experience hearing problems (Pediatric testing, n. d.). The screening should be done by Auditory Brainstem Response test (ABR) or Otoacoustic Emissions (OAE). In ABR tests, electrodes are used to estimate how the child’s brain responds to sound. The response produces waves that appear in a certain pattern. If the waves do not appear in such a prescribed pattern, then hearing loss in the child is detected. In OAE tests, the sound produced from the cochlea is analyzed. The ear can be provoked by the sound of a given magnitude through and the response of cochlea hair cells recorded. This is done by distortion product otoacoustic emissions (DPOAE) and Evoked otoacoustic emissions (EOAE) (Pediatric testing, n. d.). In addition to ABR and EOAE, children of different ages are tested using different methods.
Six-month-old children can be tested by immittance and behavioral observation. Between six months and two years, a child is tested by immittance, conditioned orientation response audiometry, and speech tests such as SRT and SRS. Children above two years of age are tested by speech tests and play audiometry. Finally, when testing functional hearing loss in children, speech tests, pure tones, hearing history, and behavioral response during history taking are considered.
Acoustic Reflex
When the sound wave enters the ear, the stapedius muscle contracts making the tympanic membrane rigid. Acoustic reflex refers to the bilateral response that the stapedius muscle has to the loud noises in both ears (Acoustic Reflexes, 2011). It is the lowest amount of contraction that can be measured. There are two types of acoustic reflex testing. In contralateral reflex testing, the sound penetration and stimulus tones occur in different ears, while in ipsilateral reflex testing, both the penetration sound and stimulus tones occur in the same ear. To measure the acoustic reflex, two sounds, namely probe tone and loud sound, are needed.
A probe tone and a loud tone to bring about reflex are introduced. As the stapedius muscle contracts, a microphone records the sound pressure level (SPL). By varying the amount of loud sound, the levels that induce reflex are recorded as an acoustic reflex. The acoustic reflex procedure may cause tone decay and loudness recruitment that are associated with retro-cochlear and cochlear pathologies, respectively (Acoustic Reflexes, 2011). This conducive pathology affects the acoustic reflexive threshold (ART) by making reflex monitoring difficult and elevating the ART in efforts to overcome hearing loss.
Masking
Sound travels through the ear by air conduction or bone conduction. Air conduction detects the degree of hearing loss, while bone conduction detects the part of the ear where the hearing loss occurs (Pure-tone testing, n. d.). Sound energy can be lost as the waves travel from the test ear to the non-test ear. This loss is called inter-aural attenuation and can be reduced by masking. Audiology masking is the process where the non-test ear is subjected to white noise to prevent it from hearing words targeted for the test ear, thereby obtaining the test ear’s true threshold.
Masking is carried out when the air-bone gap at the test ear exceeds 10dB or air conduction in the test ear at a presentation level of 40dB is great or equals either air or bone conductions at the non-test ear. It can also be done when a supra-threshold speech recognition test at 40Db exceeds or equals either borne or air conduction in the non-test ear (Intro to Audiology Masking, n. d.). Initial, maximum, and over masking should be done when certain conditions are met, as shown in Table 1. It should be noted that both maximum and over masking are only done when the Hood plateau cannot be achieved. Inter-aural attenuation depends on the insert earphones or the supra-aural earphones used. The area of contact between the insert earphone and head relates negatively to the amount of attenuation between the test ear and the non-test ear.
Table 1: Conditions for Masking
Where; MEM is the minimum effective masking level
OE is the occlusion effect
ABG is the airborne gap
ML is the masking level
NTE is the non-test ear
TE is the test ear.
Acoustic Tumors
Acoustic tumors or vestibular schwannoma are non-cancerous tumors that form in the nerve located between the inner ear and brain. It makes up 80% of all cerebellopontine angle (CPA) tumors (Acoustic Neuroma, n. d.). It mostly affects the middle-aged, where up to 20 people in a million suffer from it annually. There are two classifications of the acoustic tumor, namely sporadic, which is the most common, and rare neurofibromatosis type 2. Over time, there is an increase in the incidence of the acoustic tumor because of improved MRI tests.
The majority of such individuals also experience tinnitus, which coincides with hearing loss. Hearing loss affects 95% of people with an acoustic tumor, which means it is the most common morbidity (Acoustic Neuroma, n. d.). About half of the patients with acoustic tumors experience both dysequilibrium and vertigo vestibular effects. Facial and trigeminal nerve dysfunctions are rare in acoustic tumor patients but grow with the size of the tumor. Individuals with very large tumors have cerebellar compressive and brainstem symptoms. The tumor is detected by spontaneous nystagmus, ABR, and imaging studies such as MRI with gadolinium and CAT scans. The management measures include non-surgical such as observation and stereotactic radiography and surgical measures such as rectosigmoid and translabyrinthyne approaches. Surgery is the only treatment method for neurofibromatosis type 2.
Auditory Deprivation
Auditory deprivation occurs when hearing loss is not attended to for a long period such that the part of the brain dealing with speech processing and auditory nerves experience reduced functions. Early deprivation of the auditory system brings about disturbances in auditory perception. Research by Silman et al. (1984) shows that people with hearing problems and unaided ears experience a decrease in speech recognition compared to those with binaural and monaural aided ears (1360). The decrease in speech recognition can be a result of the impacts of auditory deprivation. The unaided ear is denied auditory stimulation because it does not get the support to receive enough sound waves. Such auditory deprivation leads to total hearing loss because of the dormancy of the sensory nerves of the brain.
The effects of binaural interference on hearing-impaired elderly individuals can be measured by binaural or monaural stimulation. Binaural stimulation brings about a greater auditory evoked response than monaural stimulation. According to Jerger et al. (1993), the response of a binaurally stimulated ear can equal the response from a good ear (129). This research shows the superiority of binaural stimulation. If the better ear in a person produces a response, but both ears produce a poor response, then there is an interference of the better ear from the bad ear.
Noise-Induced Hearing Loss
Noise-induced hearing loss (NIHL) is a hearing disorder that results from constant exposure to noise at the workplace or during recreation activities. Individuals with NIHL experience tinnitus and hyperacusis and can easily develop temporary threshold shifts (Moller, 2006, p. 178). The temporary threshold shift occurs because an individual is exposed to constant noise for a long duration such that hair cells get damaged. The NIHL also accounts for the second-most cases of sensorineural hearing losses (Moller, 2006). The high number of cases of hearing loss due to NIHL shows how dangerous the disorder is. However, this condition can be identified by the audiological evaluation. Physical examination by the clinician can also be conducted to evaluate the extent of the disorder before more advanced procedures such as MRI and ABR are carried out. Noise-induced hearing loss can be managed by amplification by hearing aids and counseling by clinicians.
Medical Imaging
Medical testing to diagnose hearing loss is important in both managing and evaluating the hearing loss. Magnetic resonance imaging and computed tomography are used to image the possible hearing loss cause. MRI is best used to check the retro-cochlear pathology while a CT scan visualizes the external and middle ear. When conducting medical imaging for hearing loss, the suspected type of hearing loss and age of the patient are considered. Considering the age is necessary because there are some imaging methods not suitable for children. The three main types of hearing loss to be considered are sensorineural hearing loss (SNHL), conductive hearing loss, and mixed hearing loss (Weissman, 1996). Screening methods such as ABR, OAE, and speech tests are supposed to be applied before MRI and CT scans are done to enable the clinician to choose the best imaging method. When it comes to age-related hearing loss(ARHL), medical imaging should target both the cochlear and the nervous system. A tone audiogram is mostly preferable to otoacoustic emissions in Medical imaging of the ARHL (Roth, 2015). The choice of an imaging method for ARHL is based on the fact that age-related hearing loss affects the temporal processing and cognitive abilities of the central neural system and a tone audiogram provides the perfect evaluation of the peripheral nervous system.
Hearing Aids
A hearing aid is electronic equipment used to magnify and change sound effectively to allow for better communication. Individuals with sensorineural hearing loss (SNHL) mostly use it. In these individuals, the inner ear’s hair cells are damaged, but a few cells are remaining. The remaining cells are the ones that receive the amplified sound and pass it to the brain as a neural signal. There are several types of hearing aid, such as for in-the-ear, behind-the-ear, pocket model, bone conduction hearing, spectacle aid, remote microphone, and in-the-canal types (Hearing Aids, n. d). The parts of the device include a battery, earpiece, receiver, microphone, and amplifier. These devices have special maintenance and care instructions. They should be free of dust, heat, and dirt. The owner should prevent dropping it and spilling liquids on it. Finally, the battery should be detached from the device when it is not in use.
Meniere’s Disease
Prosper Meniere explained a condition that he thought was an infection of the inner ear. Meniere’s disease still lacks an established etiology, but it was highly prevalent in the UK, where it was equally distributed between the genders. The disease has three clinical stages such as stage I where the symptoms of vertigo dominate, stage II where there is hearing loss fluctuation, and stage III where the hearing loss worsens (Saeed, 1998). The stages of Meniere’s disease have hearing loss which makes it necessary to consider the disease when handling hearing loss topic. The disease cannot be treated, but its management is possible.
References
Acoustic Neuroma. (n. d.). Acoustic neuroma.
Functional hearing loss. (n. d.). Functional hearing loss.
Hearing Aids. (n. d). Hearing aids.
Masking. (n. d.). Introduction to audiology masking.
Pediatric Audiology. (n. d.). Pediatric testing.
Jerger, J., Silmant, S., Lew, H. L., & Chmiel, R. (1993). Case studies in binaural interference : converging evidence from behavioral and electrophysiologic measures. Journal of the American Academy of Audiology, 4, 122–131. Web.
Moller, A. (2006). Hearing (2nd ed.). Academic Press.
Roth, T. N. (2015). Aging of the auditory system. In Handbook of Clinical Neurology (Vol. 129, pp. 357–373). Elsevier B.V. Web.
Saeed, S. R. (1998). Diagnosis and treatment of Meniere’s disease. British Medical Journal, 316(7128), 368–373.
Silman, S., Gelfand, S. A., & Silverman, C. A. (1984). Late-onset auditory deprivation: Effects of monaural versus binaural hearing aids. Journal of the Acoustical Society of America, 76(5), 1357–1362. Web.
Speech Testing. (n. d.). Speech Audiometry.
Weissman, J. L. (1996). Hearing loss.Radiology, 199(3), 593–611. Web.