Glossary

Averaging responses to anodic and cathodic stimuli to cancel the (polarity-dependent) electrical artifact while preserving the (largely polarity-independent) neural response. A simpler alternative or adjunct to forward-masking subtraction.

See also: ecap-basics

The plot of ECAP amplitude against stimulus current level. Its x-intercept gives the ECAP threshold and its slope reflects the responsiveness and survival of the stimulated neural population — a steeper slope generally indicates a healthier local neuron count.

See also: ecap-measures

A disorder of auditory nerve transmission with preserved outer-hair-cell function. In CI candidacy and follow-up, eABR and ECAP help establish whether the auditory nerve can carry an electrical signal and predict benefit.

See also: eabrclinical-cases

The upper bound of the electrical dynamic range — the loudest level that is comfortable. Called C-level by Cochlear and M-level by MED-EL/AB. The ESRT and ECAP profiles are the principal objective anchors for setting it.

See also: programmingesrt

The synchronous response of the auditory nerve to an electrical pulse delivered by the implant, recorded through a non-stimulating intracochlear electrode. A biphasic waveform with a negative peak (N1) near 0.2–0.4 ms followed by a positive peak (P2). The objective measure most central to CI fitting.

See also: ecap-basicsecap-measures

The lowest stimulus level that evokes a detectable ECAP, found by recording an amplitude growth function and extrapolating (or interpolating) to zero amplitude. Used as an objective anchor for estimating behavioural T and C levels.

See also: ecap-measuresprogramming

The range of current between T-level and C-level on an electrode, into which the acoustic input is compressed by the coding strategy. Narrow dynamic ranges are characteristic of poor neural survival.

See also: programming

The lowest electrical stimulus level that elicits a stapedius muscle contraction, observed intra-operatively under the microscope or post-operatively via immittance. Because the reflex is driven by loudness, the ESRT tends to sit near the upper comfortable level and is a useful objective ceiling for C/M-level programming.

See also: esrtprogramming

The auditory brainstem response evoked by electrical stimulation through the implant, dominated by wave eV. Used when the question concerns auditory nerve and brainstem integrity beyond what the ECAP can address — auditory neuropathy, cochlear nerve deficiency, and auditory brainstem implant candidacy.

See also: eabr

Cortical auditory evoked potentials elicited by electrical stimulation. In implanted children the latency of the P1 component indexes maturation of the central auditory pathways and tracks the existence of a sensitive period for implantation.

See also: cortical

The intracochlear portion of the implant carrying the stimulating contacts. Lateral-wall arrays sit against the outer wall of scala tympani; perimodiolar arrays curl toward the modiolus to sit closer to the spiral ganglion. Array type influences impedance, spread of excitation, and trauma risk.

See also: impedanceecap-measures

The opposition to current flow at an electrode contact, reported per channel in kΩ. Reflects the electrode-tissue interface — electrode surface, surrounding fluid, fibrosis, and new bone. Abnormally high values suggest an open circuit or encapsulation; abnormally low values suggest a short circuit.

See also: impedance

An unwanted side effect in which CI current spreads to the facial nerve, causing facial twitching. Suspected from patient report and confirmable objectively; managed by deactivating or reprogramming the offending electrodes, often guided by impedance and current-spread data.

See also: clinical-cases

The standard ECAP artifact-rejection method: a masker pulse drives the nerve into refractoriness so a following probe evokes little neural response, isolating the stimulus artifact, which is then subtracted from the unmasked probe recording to recover the true neural ECAP.

See also: ecap-basics

Recording the cochlea's own acoustically-evoked potentials (cochlear microphonic, summating potential, auditory nerve neurophonic, compound action potential) through the implant electrode during and after insertion, to detect trauma and monitor residual hearing.

See also: intraop-ecochg

The complete set of programming parameters stored in the sound processor — per-electrode T and C levels, the coding strategy, stimulation rate, pulse width, and active-electrode set. Objective measures inform, but do not replace, the behaviourally optimised MAP.

See also: programming

Cochlear Ltd's proprietary system for recording the ECAP through the implant and relaying it back via the radio-frequency link ("telemetry"). The equivalent systems are ART (MED-EL) and NRI (Advanced Bionics). AutoNRT is the automated threshold-seeking variant.

See also: ecap-basicsmanufacturers

An electrode contact with abnormally high impedance such that little or no current flows — caused by a broken wire, an extracochlear contact, or dense encapsulation. Open electrodes are usually deactivated in the MAP.

See also: impedanceclinical-cases

The latency of the cortical P1 response, used by Sharma and colleagues as a clinical index of central auditory maturation in implanted children; normal-range P1 latency after implantation indicates the central pathways are developing on track.

See also: cortical

ECAP amplitude as a function of the masker–probe interval in a forward-masking paradigm, characterising how quickly the auditory nerve recovers from refractoriness. Slower recovery has been linked to neural health and to temporal-processing limits.

See also: ecap-measures

The extracochlear return path for stimulation current (case ground and/or a ball electrode). Monopolar stimulation uses an extracochlear ground; the choice of reference affects impedance values and current spread.

See also: impedance

The brief period after a neuron fires during which it cannot (absolute) or can only with stronger stimulation (relative) fire again. Exploited by forward-masking ECAP paradigms and characterised by the recovery function.

See also: ecap-measuresecap-basics

An abnormally low-impedance condition in which two contacts are electrically connected, blurring spatial selectivity. Detected on impedance telemetry and, indirectly, on the transimpedance matrix.

See also: impedanceclinical-cases

A cochlear implant that performs poorly or produces aberrant percepts despite passing standard integrity checks. The 2005 consensus statement defines it; objective measures (impedance trends, integrity testing, ECAP) form part of the diagnostic workup.

See also: clinical-cases

The number and health of surviving spiral ganglion neurons available for electrical stimulation. Cannot be measured directly in vivo, but AGF slope, ECAP threshold, recovery function, and polarity effects are candidate non-invasive proxies.

See also: ecap-measures

The spatial extent of neural activation produced by stimulating one electrode, measured with a forward-masking ECAP paradigm in which the masker electrode is varied along the array. Broad spread implies greater channel interaction; the function's peak can also reveal electrode-position anomalies.

See also: ecap-measures

The large electrical transient produced by the stimulating current itself, which dwarfs the microvolt-scale neural response and must be removed (by forward masking, alternating polarity, or scaled-template subtraction) before the ECAP can be read.

See also: ecap-basics

The softest stimulus a recipient can reliably detect on a given electrode, the lower bound of the electrical dynamic range in the MAP. Objective measures help estimate T-levels when behavioural responses are unreliable.

See also: programming

A grid of voltages measured at every electrode while each electrode is stimulated in turn. The resulting pattern reveals electrode interactions, shorts, and — through characteristic deviations — array tip fold-over and other position anomalies, without imaging.

See also: impedance

Measurement of the voltage developed across the electrode-tissue interface during stimulation, used to verify compliance (that the device can deliver the programmed current) and to characterise the interface.

See also: impedance

The dominant, most robust peak of the electrically-evoked ABR (the electrical analogue of acoustic ABR wave V), generated in the rostral brainstem. Its presence and threshold are the usual clinical readouts of the eABR.

See also: eabr