Interpretation & Detection
Every cortical recording comes down to one judgement: is a response present or absent? Getting that judgement right — and knowing what an absent response does and does not mean — is where the test is won or lost.
Present, absent, or equivocal
A response is presentwhen a repeatable N1–P2 (or, in a child, P1) emerges clearly above the background, at the expected latency, and reproduces on a repeat average. It is absent when no such deflection rises out of the noise. The crucial third category is equivocal — a recording too noisy to call either way, which must be resolved by collecting more data, not by guessing.
Detection is fundamentally a signal-versus-noise decision. Because the response itself is large, the limiting variable is almost always the residual noise in the average. A flat trace from a noisy recording is not evidence of an absent response — it is evidence of a bad recording [11].
From visual reading to automated detection
Traditionally an experienced tester decided by eye whether a response was present — reliable in good hands, but subjective and hard to standardise. Automated statistical detection now supports that judgement: a multivariate statistic such as Hotelling’s T² tests whether the averaged waveform differs from flat noise across several time points, returning an objective present/absent decision with a known false-alarm rate[11].
Validated first in adults and then extended to infants, automated detection underpins clinical aided-CAEP systems and is especially valuable where the tester is not a cortical-response specialist[12]. It does not abolish the noise problem — a confident “absent” still requires the residual noise to have been driven low enough that a response would have shown if present.
What an absent response means — and what it doesn’t
An absent response at a given level means only that no cortical response was detected at that level under those conditions. It could mean the sound was inaudible — or that the patient drifted toward sleep, that the recording was too noisy, or that the stimulus was poorly chosen. State and noise must be excluded before an absent response is read as a threshold.
Conversely, a present response is strong evidence: sound reached and was processed by the cortex. This asymmetry is what makes the cortical response so useful in auditory neuropathy spectrum disorder, where the ABR is absent or grossly abnormal yet a present cortical response can still predict speech-perception potential [16]. The cortical response answers a question the brainstem response cannot[17].