Hearing Loss and Assistive Technologies

Multiple choice

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Short Answer Model Answers

SA1 (3 marks): (a) Conductive loss is in the outer ear (pinna, canal, eardrum) or middle ear (ossicles, Eustachian tube); sensorineural loss is in the inner ear (cochlear hair cells) or auditory nerve [1]. (b) In conductive loss the cochlear hair cells are intact and functional, if sound reaches the cochlea, transduction is normal; in sensorineural loss the hair cells are damaged/absent and cannot transduce vibration regardless of how much sound reaches them [1]. (c) Conductive → hearing aid (amplifies sound to overcome the barrier) or BAHA (bypasses outer/middle ear via bone vibration to the intact cochlea); sensorineural → hearing aid for mild-moderate loss with residual function, cochlear implant for severe-profound loss (electrode array directly stimulates the intact auditory nerve, bypassing dead hair cells) [1].

SA2 (5 marks): Structure bypassed: cochlear hair cells (organ of Corti), non-functional in profound SNHL [1]. Mechanism: an external behind-the-ear processor's microphone captures sound; a speech processor divides it into frequency bands and generates coded electrical signals; these are transmitted by radiofrequency induction across intact skin to an internal receiver-stimulator; the receiver delivers precisely timed pulses to a 12–22-electrode array threaded into the cochlea; each electrode sits at a tonotopic frequency position and directly depolarises the auditory nerve fibres there; action potentials travel via the auditory nerve to the cochlear nucleus, brainstem and auditory cortex [2.5]. Why it sounds different: the normal cochlea provides ~3,500 frequency-tuned hair cell positions (fine pitch resolution); a CI provides only 12–22 broad channels, so pitch discrimination is reduced, harmonic overtones/timbre (especially music) are poorly encoded, and the brain must learn to interpret an unfamiliar simplified signal, often described as "robotic", requiring months of rehabilitation [1.5].

SA3 (6 marks): How it works: an external sound processor analyses sound and transmits coded signals via electromagnetic induction to an internal receiver, which delivers electrical pulses through a 12–22-electrode array in the cochlea; each electrode stimulates auditory nerve fibres at a tonotopic position, bypassing non-functional hair cells [1]. Benefits: provides access to sound for those with profound SNHL who gain no benefit from hearing aids; the strongest evidence is in children, early implantation (before 12–18 months) during the critical period of auditory cortex development enables speech and language approaching hearing peers, whereas delayed implantation allows cortical reorganisation that narrows the window; in adults, CI restores meaningful communication; Medicare-funded in Australia [2]. Limitations: irreversible (destroys residual hair cells, precluding future biological therapies); does not restore natural hearing (12–22 channels vs ~3,500 hair cells → poor pitch resolution, impaired music); requires general-anaesthetic surgery and extensive rehabilitation; ineffective if the auditory nerve is damaged; outcomes vary [2]. Social/ethical dimension: implanting young children is ethically complex because the child cannot consent to an irreversible procedure; some in the Deaf community view deafness as a cultural identity (with its own language, Auslan, and community) rather than a deficit to be corrected, and argue implantation without consent denies the child a Deaf identity, a genuine tension between the medical and social models of disability [1].