What ABR can and cannot tell you

ABR samples the auditory pathway up to the inferior colliculus and stops. Lesions above — thalamocortical, primary auditory cortex, association cortex — leave the ABR untouched¹. A normal ABR in a patient with disproportionate listening-in-noise difficulty is itself a finding: it redirects the workup away from the periphery and brainstem and toward central processing.Foundation

CAPD — central auditory processing disorder

CAPD describes a heterogeneous group of difficulties with the efferent and cortical handling of auditory input despite normal peripheral hearing². Diagnosis rests on a behavioural test battery: speech-in-noise with controlled SNR, dichotic digits, dichotic sentences, frequency or duration patterns, and gap detection. ABR is part of the workup to confirm that the periphery and brainstem are not the bottleneck.

The middle-latency response (MLR) Trainee

The MLR is the next evoked-potential layer above the ABR, between roughly 10 and 80 ms³. Its Na–Pa complex reflects thalamocortical and primary auditory-cortex generators. A normal ABR with an abnormal MLR localises a lesion above the inferior colliculus — usually thalamic or cortical. MLR is technically more demanding than ABR (sensitive to sleep state and electrode position) but adds anatomical reach when needed.

P300 and cortical ERPs

The P300 is a cognitive event-related potential reflecting attention and stimulus evaluation in associative cortex around 300 ms. It is used in research and select clinical settings; not a routine workup component.

When central testing matters

Children failing in noisy classrooms despite normal audiograms, adults reporting disproportionate difficulty after acoustic neuroma surgery or radiation, post-stroke or post-TBI patients with hearing complaints exceeding their audiogram — these are the populations in whom the ABR-MLR-behavioural battery yields the most. Clinician

Findings

ABR — normal
Audiogram — normal or near-normal
Speech-in-noise — disproportionately impaired
Dichotic digits — asymmetry or below-norm
MLR Na–Pa — may be abnormal in cortical lesions

Trace

Click ABR · 80 dB nHL · normal — central pathology is invisible to ABR.

References

Kraus N, McGee T. The middle latency response generating system. Electroencephalogr Clin Neurophysiol Suppl 1995;44:93–101.
American Speech-Language-Hearing Association. Central Auditory Processing: Current Status of Research and Implications for Clinical Practice. ASHA Technical Report, 1996.
Musiek FE, Chermak GD. Handbook of Central Auditory Processing Disorder (2nd ed.). Plural Publishing, 2014.
Bellis TJ. Assessment and Management of Central Auditory Processing Disorders in the Educational Setting (2nd ed.). Plural Publishing, 2003.