Biology • Year 12 • Module 8 • Lesson 18
Hearing Loss, Cochlear Implants and Bone Conduction
Build HSC Band 5–6 extended-response technique: evaluate evidence, match technology to patient, and assess the claim that “cochlear implants restore hearing.”
1. Extended response — data-driven evaluation of cochlear implant technology (Band 5–6)
8 marks Band 5–6
Stimulus — Maya’s case. Maya is identified at newborn hearing screening as having profound bilateral sensorineural hearing loss. Audiological workup confirms that cochlear hair cells in both ears are non-functional; MRI confirms bilateral auditory nerves are intact. At age 8 months, bilateral cochlear implantation is recommended by the Australian Cochlear Implant Program.
The table below summarises Australian trial data comparing language outcomes for three groups of profoundly deaf children at age 7 years.
| Group | n | Mean receptive language age-equivalent (months) | % attending mainstream school with no additional support |
|---|---|---|---|
| Implanted <12 months | 42 | 83 | 71% |
| Implanted 12–24 months | 61 | 74 | 52% |
| No implant (hearing aid only) | 28 | 49 | 18% |
Table 1. Language outcomes at age 7 years for profoundly deaf children. Adapted from Dettman et al. (2016), Ear & Hearing 37: 461–471 (Melbourne CI Program).
Q1. Evaluate cochlear implantation as a technology to assist Maya, using the stimulus data and your lesson knowledge. In your response you must:
- Describe the mechanism by which a cochlear implant provides hearing to Maya, naming the specific structure it bypasses.
- Use the table to assess the benefit of early implantation (<12 months) compared with both later implantation (12–24 months) and hearing aid use alone.
- Identify two specific biological limitations of cochlear implantation, using lesson content to explain each.
- Consider one social or ethical dimension specific to cochlear implantation in an infant.
- Reach a justified overall recommendation for Maya, explicitly referencing data from the table.
2. Evaluate this claim — “cochlear implants restore hearing” (Band 5–6)
7 marks Band 5–6
“Cochlear implants restore hearing. They are now so advanced that a cochlear implant recipient experiences sound in exactly the same way as someone with normal hearing. There is no meaningful difference between natural hearing and cochlear implant hearing, and the technology makes all other hearing assistive devices unnecessary.”
Paraphrased from an online health article, 2023.
Q2. Evaluate the claim above. In your response:
- Identify which elements (if any) of the claim are partially correct, and explain why using lesson knowledge.
- Identify the specific biological errors in the claim, explaining the correct science for each error.
- Explain why hearing aids and BAHA remain necessary and appropriate technologies for specific patient groups despite the existence of cochlear implants.
- Reformulate the claim into a biologically accurate statement using HSC terminology.
Q1 — Sample Band 6 response (8 marks), annotated
Mechanism [1]: A cochlear implant bypasses Maya’s non-functional cochlear hair cells — the specific structure that is damaged in her sensorineural hearing loss. An external sound processor captures incoming sound, divides it into frequency bands, and transmits coded electrical signals via radiofrequency induction through skin to an internal receiver-stimulator. This delivers precisely timed electrical pulses to an electrode array (12–22 electrodes) threaded into the cochlea. Each electrode stimulates auditory nerve fibres at a specific tonotopic position, generating action potentials that travel via the auditory nerve to the auditory cortex, producing sound perception.
Data-supported benefit [2]: Table 1 shows that children implanted before 12 months achieve a mean receptive language age-equivalent of 83 months at age 7 (a 7-year-old child demonstrating nearly 7-year-old language ability), compared with 74 months for those implanted at 12–24 months and only 49 months for those using hearing aids alone. The proportion attending mainstream school without support is 71% in the earliest-implanted group, versus 52% for the 12–24 month group and only 18% for the hearing-aid group. This demonstrates a clear, stepwise benefit of earlier implantation that is clinically and educationally significant [1 for citing table data; 1 for interpreting the educational/language significance].
Limitation 1 [1]: Cochlear implantation is irreversible: threading the electrode array into the scala tympani destroys Maya’s residual cochlear hair cells. This eliminates the future possibility of biological therapies (e.g. hair cell regeneration from stem cells, which are under active research) that might otherwise restore more natural cochlear function.
Limitation 2 [1]: The cochlear implant does not restore normal hearing. With 12–22 electrode channels representing the audible frequency range versus ~3,500 hair cell positions in the normal cochlea, spectral resolution is coarse. Maya will perceive a degraded signal — she may achieve good speech recognition but will experience significant difficulty with music appreciation and in noisy environments. She requires extensive, ongoing auditory rehabilitation.
Ethical dimension [1]: Maya is 8 months old and cannot consent to an irreversible medical procedure. Some within the Deaf community (including Australian Deaf advocates) argue that cochlear implantation of young children without consent denies them the right to develop a Deaf identity within Deaf culture (including Auslan), which has its own language, community, and social structures. This is a genuine tension in Australian healthcare ethics between the medical model (deafness as disability requiring correction) and the social model (deafness as cultural difference).
Justified recommendation [1]: Bilateral cochlear implantation is recommended for Maya at 8 months. Hearing aids are ineffective because she has no functional hair cells to transduce the amplified signal. BAHA is inappropriate because it requires a functional cochlea — which Maya lacks. The Table 1 data strongly support early implantation: at <12 months, 71% of children attend mainstream school with no support and mean language age-equivalent is 83 months — outcomes that are substantially superior to all other options. The ethical complexity is acknowledged, but the evidence of benefit during the critical period of neural development supports early implantation as the optimal medical recommendation for Maya.
Marking criteria:
- 1 — Correctly describes the cochlear implant mechanism, naming hair cells as the bypassed structure and electrode array as the direct nerve stimulator.
- 1 — Uses specific data values from Table 1 to demonstrate the benefit of early (<12 month) implantation over later implantation.
- 1 — Interprets the educational / language significance of the data differences (not just restates them).
- 1 — Identifies irreversibility as a biological limitation and explains the specific consequence (destroys residual hair cells / forecloses future biological therapies).
- 1 — Identifies the limitation that CI does not restore natural hearing and explains the biological reason (12–22 channels vs ~3,500 hair cell positions / coarse spectral resolution).
- 1 — Considers the ethical dimension of infant consent / Deaf community perspectives on cochlear implantation.
- 1 — Eliminates other technologies (hearing aid, BAHA) with explicit biological reasons and reaches a justified recommendation for cochlear implantation.
- 1 — Explicitly references data values from Table 1 in the recommendation (e.g. 71% mainstream school attendance / SLQ advantage).
Q2 — Sample Band 6 response (7 marks), annotated
Overall judgement [1]: The claim is largely incorrect and contains multiple specific biological errors. While cochlear implants are transformative and effective for patients with profound sensorineural hearing loss, they do not restore normal hearing, the signal they provide is biologically distinct, and they do not make other assistive devices unnecessary.
Partially correct element [1]: The claim that cochlear implants are “advanced” and have significantly improved outcomes is defensible. Modern digital processing, expanded electrode arrays (up to 22 electrodes), and improved signal processing algorithms have substantially improved speech recognition in quiet for CI users compared with earlier devices. Many CI users do achieve high speech recognition rates in optimal listening conditions.
Error 1 — “Restores hearing / exactly the same as normal hearing” [1]: A cochlear implant does not restore normal hearing. The normal cochlea has approximately 3,500 inner hair cell positions providing continuous tonotopic frequency resolution. A cochlear implant has 12–22 electrodes, each stimulating a broad cochlear region. This coarse spectral representation means pitch discrimination is significantly impaired — CI users typically struggle to recognise melodies, distinguish instrument timbres, and perceive the harmonic structure of music. The signal is described as “robotic” or “electronic” initially and requires months of auditory rehabilitation for the brain to interpret. The correct statement is that a cochlear implant provides “access to sound” via a different electrical signal, not that it restores natural hearing.
Error 2 — “Makes all other hearing assistive devices unnecessary” [1]: Cochlear implants are appropriate only for severe-to-profound sensorineural hearing loss with an intact auditory nerve. Hearing aids remain appropriate and non-invasively effective for patients with mild-to-moderate sensorineural hearing loss who have sufficient residual hair cell function. BAHA remains the technology of choice for patients with conductive hearing loss (intact cochlea, outer/middle ear problem) such as otosclerosis or bilateral atresia/microtia, for whom cochlear implantation would destroy functional cochleae unnecessarily. An intact auditory nerve is required for a cochlear implant to function — if the nerve is damaged, CI will not work and other approaches are needed.
Why other devices remain necessary [1]: Each technology fills a distinct clinical niche matched to the type and location of hearing loss. Hearing aids amplify airborne sound for patients who still have functional hair cells; BAHA transmits vibrations through bone for patients whose outer/middle ear cannot conduct sound but whose cochlea is functional; cochlear implants bypass non-functional hair cells for patients whose cochleae cannot transduce sound but whose auditory nerves are intact. No single technology is appropriate for all patients.
Reformulated claim [1]: “Cochlear implants are the most effective available technology for patients with severe-to-profound sensorineural hearing loss and an intact auditory nerve. They provide access to sound by directly stimulating the auditory nerve with electrical pulses from an electrode array, bypassing non-functional cochlear hair cells. The electrical signal they provide differs from natural hearing in spectral resolution and quality, requiring auditory rehabilitation. For other types of hearing loss — including mild-to-moderate sensorineural loss and conductive loss — hearing aids and bone-anchored hearing aids remain the appropriate and effective first-line technologies.”
Marking criteria:
- 1 — States an explicit overall evaluative judgement (partially/largely incorrect, with specific flaws).
- 1 — Correctly concedes what is defensible in the claim (advanced technology; improved speech recognition in quiet).
- 1 — Identifies and corrects the “restores / same as normal hearing” error using the biological mechanism (12–22 channels vs ~3,500 hair cell positions; coarse spectral resolution; different signal).
- 1 — Identifies and corrects the “makes all other devices unnecessary” error (hearing aids and BAHA serve different patient populations and types of hearing loss).
- 1 — Explains why hearing aids remain appropriate using the concept of residual hair cell function.
- 1 — Explains why BAHA remains appropriate using the concept of intact cochlea in conductive hearing loss.
- 1 — Reformulates the claim into a biologically accurate statement using HSC terms (sensorineural hearing loss, hair cells, auditory nerve, electrode array, conductive hearing loss).