CI Atlas · Compare
Compare the objective measures
Every measure in this atlas samples a different point along the auditory pathway — from the electrode–tissue interface, through the nerve and brainstem, to the cortex — and answers a different question. This page sets them side by side so you can pick the right tool for the clinical question in front of you, and see where each one stops. Each row links to its full module; the cross-brand terminology sits in Module 11.
Objective measures at a glance
| Measure | What it samples | Timing | Question it answers | Primary clinical use | Key limitation |
|---|---|---|---|---|---|
| Impedance & TIM | Electrode–tissue interface | Instant (seconds, no response needed) | Can current flow? Is the contact intact, and where is the array? | Every session — open/short detection, array position, compliance | Says nothing about whether the nerve is there to respond |
| ECAP — basics (NRT) | Distal auditory nerve (N1–P2) | ~0.2–0.5 ms post-stimulus | Does the auditory nerve fire to electrical stimulation? | Confirming a neural response; the basis for level estimation | Dominated by stimulus artifact; not proof of central transmission |
| ECAP — measures | Auditory nerve (threshold, AGF, recovery, spread) | ~0.2–0.5 ms post-stimulus | Where is threshold, how does the response grow and spread? | Level estimation (tNRT), neural-health proxies, channel interaction | Indirect proxy; absolute values are brand-specific |
| ESRT | Brainstem reflex arc (stapedius muscle) | Reflex (tens–hundreds of ms) | Where is the upper, comfortable loudness level? | Anchoring the C/M (comfortable) level in the MAP | Not always obtainable; sensitive to anaesthesia intra-operatively |
| eABR | Auditory nerve → rostral brainstem (wave eV) | ~2–4 ms post-stimulus | Does the signal reach the brainstem? Is the pathway viable? | ANSD, cochlear-nerve deficiency, CI-versus-ABI candidacy | An absent response is hard to interpret; technically demanding |
| Cortical (P1) | Auditory cortex (P1-N1-P2 complex) | ~50–300 ms post-stimulus | Is the central auditory pathway maturing? | Tracking maturation in implanted children (the sensitive period) | Needs an awake, cooperative child; not a speech-understanding test |
| Intra-op ECochG | Cochlear hair cells / neurons (acoustically evoked) | Stimulus-locked, real-time during insertion | Is the cochlea being traumatised as the array goes in? | Hearing-preservation surgery; live insertion feedback | Intra-operative only; amplitude alone is an imperfect trauma marker |
The measures form a sequence, not a menu: impedance clears the interface, the ECAP asks the nerve, the ESRT bounds loudness, the eABR and cortical responses probe the pathway above the nerve, and intra-operative ECochG protects the cochlea during surgery. A complete picture usually combines several — and no single measure substitutes for a behavioural map where one can be obtained.
Compare across manufacturers
The same physiology carries different names, defaults, and units across makers. Explore the cross-brand comparison below — deliberately broader than the “big three” — and see Module 11 for the full terminology map.