Glossary

ROC-derived click SP/AP cutoff of 0.34 for superior canal dehiscence (Adams 2015; 92.3% sens, 94% spec). The same patient with hydrops would also exceed this; the discriminating clinical features are the audiogram (air–bone gap), VEMP threshold, and CT.

See also: scd

Averaging the responses to alternating rarefaction and condensation clicks. Cancels the CM (which inverts with each click) and leaves SP + AP clean. The default for SP/AP-based clinical protocols; switched off when the question is about the CM.

See also: technique

Far-field scalp recording of waves I–V generated by the auditory nerve (wave I) up through the lateral lemniscus / inferior colliculus (wave V). The non-invasive partner to ECochG: ABR adds the brainstem-level waves II–V that ECochG cannot record. Used together they cover the entire peripheral auditory pathway.

See also: abr-overlap

Failure of synchronous auditory nerve transmission with preserved cochlear hair-cell function. ECochG signature: present CM (inverts with click polarity), absent or grossly reduced AP. Site of lesion is heterogeneous — presynaptic (IHC ribbon synapse, OTOF), postsynaptic (dendrites), or demyelinating/axonal (OPA1).

See also: ansd

2015 international consensus criteria for diagnosing Ménière's disease (Lopez-Escamez et al.). Define 'definite' (vertigo episodes 20 min–12 h, audiometrically documented low-frequency SNHL on at least one occasion, fluctuating aural symptoms) and 'probable' (broader duration window, no audiometric requirement). Supersedes the 1995 AAO-HNS guideline.

See also: menieres

Membrane separating scala media from scala tympani; supports the organ of Corti. Mechanical traveling wave along the basilar membrane in response to sound is the basis of cochlear frequency analysis (von Békésy 1960) — high frequencies at the base, low frequencies at the apex.

See also: anatomy

Four-step authenticity protocol for confirming a recorded oscillation is a real cochlear microphonic rather than radiated stimulus artifact (Berlin 1998): rarefaction only → condensation only → block the insert phone tube → alternating polarity. A true CM inverts with click polarity and disappears when no acoustic stimulus reaches the ear.

See also: ansd

A CM amplitude drop ≥ 30% from the prior running maximum during cochlear implantation, used as the surgical-intervention trigger in the Campbell 2022 RCT. Triggers pause, withdraw ~2 mm, reposition, and resume — the protocol shown to preserve residual hearing.

See also: intraop-ci

Frequency-swept stimulus — broadband, but with low frequencies delivered earlier and high frequencies later, by an interval matched to the cochlear traveling-wave delay (Elberling 2007). Boosts the AP because the cross-frequency neural volley is more synchronous; at the cost of a smaller, less reliable CM.

See also: technique

Brief (~100 µs) electrical pulse delivered to the insert phone, producing a broadband acoustic transient. The default ECochG stimulus for screening and for any question that turns on the CM (auditory neuropathy in particular).

See also: technique

An alternating-current potential that follows the stimulus waveform, generated mostly by outer hair cell receptor currents. The CM is the diagnostic signature of preserved hair-cell mechanoelectrical transduction in suspected ANSD; the Berlin polarity-reversal protocol confirms that a recorded oscillation is biological rather than radiated stimulus artifact.

See also: normal-wavesansd

Loss of IHC ribbon synapses without hair-cell loss — preferentially the low/medium-spontaneous-rate fibres that encode suprathreshold and in-noise temporal information. The audiogram is normal; the suprathreshold neural code degrades. Robust in animal models (Kujawa 2009); the human translation is contested.

See also: synaptopathy

Perilymph-specific protein detectable in middle-ear lavage when perilymph has escaped (Ikezono 2009). A biochemical alternative to functional ECochG testing for perilymph fistula where the assay is available; high specificity for the presence of perilymph in the middle ear.

See also: perilymph-fistula

The synchronous spike volley of distal auditory nerve fibres at the cochlear base, recorded as a large negative peak around 1.5–2.0 ms after a click at 90 dB nHL. The AP is the same physiological event as ABR wave I — recorded much closer to its generator on ECochG.

See also: normal-wavesabr-overlap

Hallowell Davis's 1965 conceptual framework treating the endocochlear potential as the bias voltage that drives hair-cell mechanoelectrical transduction. Still the standard explanation for CM and SP generation half a century later.

See also: intro

The +80 mV resting potential of endolymph in scala media, maintained by the stria vascularis. Davis's 'battery model' (1965) treats it as the bias voltage that drives hair-cell receptor currents.

See also: anatomy

Distension of the endolymphatic compartment (scala media), with bulging of Reissner's membrane into scala vestibuli. Demonstrated histologically in Ménière's disease (Kimura 1967); the mechanical chain underlies the ECochG SP elevation.

See also: menieres

Click SP/AP amplitude ratio ≥ 0.40 used as the classical threshold for endolymphatic hydrops in Ménière's disease (Ferraro & Tibbils 1999). Sensitivity ~53–70%; specificity ~80–90% against the 1995 AAO-HNS criteria.

See also: menierestools

More-sensitive alternative click SP/AP cutoff of 0.30 for Ménière's disease, advocated by Gibson and colleagues (Gibson 2017). Lower threshold trades some specificity for catching hydropic ears that the Ferraro 0.40 cutoff misses.

See also: menieres

Small openings in the bone at the modiolus through which Type I auditory nerve fibres pass as they leave the cochlea. The distal AP generator sits at this level — peripheral to where most vestibular schwannomas arise, which is why ECochG is insensitive to retrocochlear pathology.

See also: schwannoma

Pressure-induced vertigo — Valsalva, sneezing, or ear-canal pressure mechanically deflecting the cupula via a third window. Classically seen in SCD; can also occur in perilymph fistula and large vestibular aqueduct.

See also: scd

Single row of pear-shaped sensory cells on the modiolar side of the organ of Corti. Each IHC synapses with roughly 10–20 Type I auditory nerve afferents via ribbon synapses. IHCs are the principal sensory transducers; outer hair cells provide amplification.

See also: anatomysynaptopathy

SP/AP ratio in the symptomatic ear minus the same measure in the contralateral ear, typically using the > 0.10–0.15 cutoff. Useful when bilateral disease is unlikely — the contralateral ear is the best normative control any individual patient has.

See also: menieres

ECochG recorded from one of the implanted electrode contacts of a cochlear implant, using the CI's own back-telemetry amplifier (Campbell 2015). Records ~25× the tiptrode amplitude with no extra hardware in the surgical field — the enabling technology for intraoperative monitoring during CI insertion.

See also: intraop-ci

Plot of AP latency against stimulus intensity. Picton 1981 published the canonical normative band. Conductive losses give a parallel rightward shift; cochlear losses with recruitment give a steep slope near threshold that rolls over to normal latency at high intensities; retrocochlear pathology keeps latency prolonged at all intensities.

See also: normal-waves

Group-level SP/AP range of 0.35–0.60 reported in noise-exposed normal-audiogram adults with elevated suprathreshold ECochG findings (Liberman 2016). Used in research settings; not a validated cutoff for individual diagnosis of cochlear synaptopathy.

See also: synaptopathy

Clinical syndrome of episodic vertigo (20 min–12 h), fluctuating low/mid-frequency SNHL, tinnitus, and aural fullness. Histopathological substrate is endolymphatic hydrops. Diagnosed per the 2015 Bárány criteria (clinical); ECochG is supportive but not required.

See also: menieres

The sensory epithelium sitting on the basilar membrane in scala media. Contains one row of inner hair cells (the primary sensory cells) and three rows of outer hair cells (the cochlear amplifier). Innervated by Type I afferents from the spiral ganglion (95% of fibres) and Type II afferents (5%).

See also: anatomy

Protein essential for vesicle fusion at the IHC ribbon synapse. Loss-of-function OTOF mutations are the prototypical cause of presynaptic ANSD: the IHC ribbon synapse fails while auditory nerve dendrites remain intact. CI typically gives excellent outcomes because the implant bypasses the failed synapse.

See also: ansd

Three rows of cylindrical cells on the lateral side of the organ of Corti. Carry prestin in their lateral wall and undergo electromotile length changes that amplify basilar-membrane motion at low intensities (the cochlear amplifier). The CM is generated mostly by OHC receptor currents.

See also: anatomy

Membrane-covered opening between the middle ear and scala vestibuli, occupied by the footplate of the stapes. The site at which acoustic energy enters the cochlea.

See also: anatomy

Abnormal communication between the perilymphatic space and the middle ear, allowing perilymph to escape. Classic settings: post-stapedectomy, barotrauma, head trauma, or spontaneous. Diagnosis is difficult — Gibson's 1992 postural-change ECochG protocol is one functional test; cochlin-tomoprotein assay is the more specific biochemical alternative.

See also: perilymph-fistula

Recording rarefaction and condensation clicks separately and looking for 180° inversion of the early oscillation between the two runs. A true biological CM inverts; radiated electrical artifact does not. The cornerstone of the Berlin 1998 authenticity protocol for diagnosing ANSD.

See also: ansd

Thin two-layer membrane separating scala vestibuli (perilymph) from scala media (endolymph). Distends upward into scala vestibuli in endolymphatic hydrops; the resulting shift of the basilar-membrane operating point underlies the SP elevation seen on ECochG in Ménière's disease.

See also: menieres

Specialised synapse at the IHC base, characterised by an electron-dense ribbon that tethers vesicles for rapid sustained release. Each IHC carries ~12 ribbon synapses, divided between high-spontaneous-rate fibres (threshold detection) and low/medium-spontaneous-rate fibres (suprathreshold and in-noise coding). Selective loss of the low/medium-SR ribbons is the cochlear-synaptopathy hypothesis.

See also: synaptopathy

Membrane-covered opening between scala tympani and the middle ear, providing the second compliant point in the otic capsule (the oval window is the first). Acoustic energy exits the cochlea via the round window. The round-window niche is the canonical site for transtympanic ECochG electrode placement.

See also: technique

Endolymph-filled middle chamber containing the organ of Corti. Bounded above by Reissner's membrane and below by the basilar membrane. Endolymph has a high K⁺ and low Na⁺ composition and is held at the +80 mV endocochlear potential by the stria vascularis.

See also: anatomy

Lower perilymph-filled chamber of the cochlea, bounded above by the basilar membrane and below by the bony otic capsule. Acoustic energy exits via the round window. Perilymph composition mirrors CSF (high Na⁺, low K⁺).

See also: anatomy

Upper perilymph-filled chamber of the cochlea, bounded above by the bony otic capsule and below by Reissner's membrane. Acoustic energy enters via the oval window and propagates apically.

See also: anatomy

Dimensionless ratio of SP magnitude to AP magnitude, both measured from pre-stimulus baseline. Electrode-independent so values from different electrode sites (tiptrode, TM, transtympanic, intracochlear) are directly comparable. Cutoffs: Ferraro 0.40 (Ménière's), Gibson 0.30 (more sensitive Ménière's), Adams 0.34 (SCD), Liberman 0.35–0.60 (synaptopathy range).

See also: menieresscdsynaptopathytools

Ratio of the integrated areas under the SP and AP components rather than their peak amplitudes. Ferraro 1999 originated the measure; Bawazeer 2024 reports 88.5% sensitivity and 70% specificity for Ménière's at TT recording. Less affected by AP shrinkage than the amplitude ratio when hearing loss is substantial.

See also: menieres

Vascularised epithelium on the lateral wall of scala media. Responsible for active K⁺ recycling that maintains the +80 mV endocochlear potential — the battery driving hair-cell mechanoelectrical transduction (Davis 1965).

See also: anatomy

Sensorineural loss ≥ 30 dB over three contiguous audiometric frequencies, developing in 72 hours or less. 71–90% are idiopathic; 1–5% harbour a vestibular schwannoma. The 2019 AAO-HNSF guideline recommends MRI or ABR (not ECochG) for retrocochlear workup.

See also: ssnhl

A direct-current shift that persists through the stimulus interval, generated by a mixture of hair-cell receptor currents and dendritic post-synaptic activity (Pappa 2019, Hutson 2022). Elevation of the SP relative to the AP is the canonical ECochG signature of endolymphatic hydrops and of third-window pathology.

See also: normal-wavesmenieresscd

Bony defect over the superior semicircular canal, creating a third compliant window on the inner ear. Symptoms: sound- and pressure-induced vertigo, autophony, pulsatile tinnitus, low-frequency air–bone gap with intact bone conduction. Diagnostic gold standard is high-resolution temporal bone CT; ECochG (Adams 0.34 cutoff) and VEMPs are supportive.

See also: scd

Any pathology that creates a third compliant point on the bony labyrinth in addition to the oval and round windows — most commonly SCD, but also cochlea-facial nerve dehiscence (Wackym 2019) and large vestibular aqueduct. Acoustic energy is shunted, intracochlear pressure dynamics shift, and the SP/AP ratio rises.

See also: scd

Gold-foil-wrapped foam insert electrode placed in the external ear canal. The least invasive ECochG electrode and the workhorse of clinical practice in most centres. Records ~1× the baseline AP amplitude (typical 0.5–1.5 µV at 90 dB nHL); needs 1000–2000 sweeps to give clean averages.

See also: technique

Soft-tipped electrode resting against the tympanic membrane. Records ~3× the tiptrode amplitude with comparable patient tolerance; typical clinical sweep count 500–1000.

See also: technique

Brief windowed sinusoid — typical clinical setting: 1 or 2 kHz carrier, 1–2 ms linear rise/fall, 10 ms plateau, alternating polarity, 90 dB nHL. The plateau yields a sustained SP that is more reliably measured than the click SP shoulder; tone-burst protocols therefore raise Ménière's sensitivity from ~60% (click amplitude alone) to ~85–92%.

See also: techniquemenieres

Needle electrode passed through the tympanic membrane onto the cochlear promontory under local anaesthesia. Records ~10× the tiptrode amplitude — large, clean signals — at the cost of invasiveness; typical sweep count 200–500. Default for transtympanic Ménière's protocols in some centres.

See also: technique

Sound-induced vertigo. Classically seen in superior canal dehiscence where loud sounds drive endolymph through the dehiscence into the affected canal. Present in ~50% of SCD patients.

See also: scd

Reflex myogenic response to acoustic or vibration stimuli, sampling otolith function. cVEMP (cervical, sternocleidomastoid) tests saccular function; oVEMP (ocular, inferior oblique) tests utricular function. Lowered thresholds and augmented amplitudes are sensitive and specific for SCD.

See also: scd

Benign tumour arising from Schwann cells of the vestibular division of CN VIII, typically in the IAC or at the CPA. Gadolinium-enhanced MRI is the diagnostic gold standard (near-100% sensitivity at 2–3 mm). ECochG is insensitive because the AP generator sits peripheral to most tumours.

See also: schwannoma

The first peak of the auditory brainstem response, generated by the distal auditory nerve at the cochlear base. Wave I and the ECochG AP are the same physiological event recorded with different geometry; tympanic or transtympanic ECochG can salvage an unreliable scalp wave I when an I–V interpeak interval is needed.

See also: abr-overlap

The most robust peak of the auditory brainstem response, generated in the lateral lemniscus / inferior colliculus. Not recordable on ECochG — its generators are too far from the cochlear-end recording sites. Wave V latency and the I–V interpeak interval are the principal retrocochlear markers on ABR.

See also: abr-overlap

The 1930 observation by Wever and Bray that the cat auditory nerve produces a microphone-like response to sound. Subsequently resolved into hair-cell-generated CM and neural activity; the historical starting point of cochlear electrophysiology.

See also: intro