Normal Waves I–VII
The canonical adult ABR at 80 dB nHL click. Memorise the three peaks and three intervals, then learn how they move with age, sex, and intensity.
The three landmarks
At 80 dB nHL click, the normal adult ABR shows wave I at 1.6 ms, wave III at 3.8 ms, and wave V at 5.6 ms[3]. Standard deviations are tight (0.15–0.25 ms), reflecting the highly synchronised neural volley that produces a far-field response. Latency limits are the means + 2 SD; values beyond suggest pathology.
The three intervals
IPL I–III 2.2 ms, IPL III–V 1.8 ms, IPL I–V 4.0 ms. The interpeak intervals are biologically more stable than the absolute latencies because they cancel out peripheral conductive influences[12].
| Measure | Mean | SD |
|---|---|---|
| Wave I | 1.6 ms | 0.15 |
| Wave III | 3.8 ms | 0.20 |
| Wave V | 5.6 ms | 0.25 |
| IPL I–III | 2.2 ms | 0.15 |
| IPL III–V | 1.8 ms | 0.20 |
| IPL I–V | 4.0 ms | 0.25 |
| ILD V | upper limit 0.4 ms | |
Latency–intensity function
As stimulus intensity drops, wave V latency rises at about 0.03 ms per dB — the canonical L–I slope[13]. Wave I disappears into the noise floor first (around 50 dB nHL); wave V persists to threshold (typically 20 dB nHL in adults).
Maturation
ABR is mature surprisingly late. At term, wave V latency is around 7 ms — the eighth nerve has matured but central conduction has not. By 18–24 months, the response is essentially adult[14]. Norms for paediatric ABR must use age-appropriate tables.
Sex and head-size effects
Adult women have shorter wave V latency than men by about 0.15 ms, attributable to shorter axonal path length[15]. Head-size and brain-volume effects on IPL I–V have been described and are small but real.
Interaural wave V difference
The within-subject interaural V latency difference is the single most sensitive ABR feature for retrocochlear pathology — historically the basis for screening before MRI became routinely available. Upper limit of normal: 0.4 ms.