Finally, the receiver converts this modified and amplified electrical signal back into sound with the help of electromagnetism which is similar to how headphones work. Thus, the sound signal can be altered by the user or clinician to suit the type of hearing loss. The signal then goes through a filter which is used to change the relative amplitude of the high, mid and low frequency characteristics of a signal. Compression amplifiers are used to amplify the signal while avoiding distortion and decreasing its dynamic range and can represent sound in either an analogue (mimicking acoustic waveforms) or digital (representing signals as a string of numbers) manner. These small signals generated by the microphone are sent to the amplifier which makes them more powerful. A more sophisticated type of an omnidirectional microphone is an “adaptive directional microphone” which works together with the hearing aid’s noise reduction technology to highlight speech sounds and important environmental sounds while suppressing background noise.
These microphones may be unidirectional, bidirectional or omnidirectional. The microphone is the first component to receive the sound signal and it converts this energy into electricity. The modern digital hearing aid is a marvel of sophisticated engineering and miniaturization. Oto-Acoustic Emissions (OAE) –This involves recording of a low-level sound emitted by the cochlea either spontaneously or evoked by an auditory stimulus thus indicating integrity of the outer hair cells of the cochlea.Ĭortical Auditory Evoked Potentials (CAEP) –This test is an objective and non-invasive assessment of electrical activity from the level of the inferior colliculus to the primary auditory cortex in response to sound stimulus.Īided Audiometry –This test is similar to PTA but involving the estimation of hearing thresholds during the use of a hearing prosthesis. Speech Audiometry– This test provides information concerning hearing for speech, the type and degree of hearing impairment, and to check the reliability of the pure tone thresholds.īrainstem Evoked Response Audiometry (BERA) –This test is an objective and non-invasive method of hearing assessment which detects electrical activity along the auditory pathway (from inner ear to inferior colliculus) in response to sound impulse. Pure Tone Audiometry (PTA)– This is a subjective test involving hearing threshold evaluation in both air conduction and bone conduction. After the clinical assessment, the candidacy process involves a complete audiological evaluation using the following tests. It is important to identify patients in whom medical or non-prosthetic surgical management of their hearing loss should be attempted prior to dispensing of the hearing device. In either situation, the pre-audiometric assessment which involves collection of relevant medical history and clinical examination of the hearing-impaired person is an important first step of the auditory rehabilitation process. Often, it is not the individual themselves, but the family member/caretaker who notes that the concerned individual is struggling with their hearing impairment. Hearing impaired individuals usually seek help only when they have reached a stage that they can no longer ignore their hearing loss. The prosthetic devices currently being used for restoration of hearing are classified based on their mode of action in Figure 1. Surgical restoration of hearing involves procedures that range from ossicular reconstruction to implantation of devices which serve to assist the functioning of the auditory pathway. Hearing impairment results from damage or disease anywhere along the auditory pathway. This has consequences on the child’s development of language, social skills and cognition. In addition, the deaf child is unaware of sounds of the outside environment, and thus, is centered on self and own activities. The deaf child cannot listen to her or his mother and focus on an activity simultaneously since both inputs must be processed visually.
Older people with moderate or more severe hearing loss were more likely to feel depressed and suffer with poor mental health. Hearing impairment has a significant bearing on many aspects of an individual’s life, including their socioeconomic status, mental well-being, education and employment opportunities. It is estimated that the number of people with deafness will grow to 630 million by 2030 and maybe over 900 million by 2050. The global burden of disabling hearing impairment is estimated at 466 million people (6.1% of the world’s population) where 432 million (93%) of these are adults (242 million males, 190 million females) and 34 million (7%) children.