A comparison of ABR & Cortical ERA as threshold estimation tests
Since both the auditory brainstem response (ABR) and Cortical ERA can be used for threshold estimation, it is worth briefly highlighting the pros and cons of the two techniques.
ABR responses are generally less variable, more robust and essentially immune from the patient's mental state and can conveniently be recorded in sleep, under general anaesthesia or with the patient physically relaxed. However, the presence of excess myogenic (muscle) activity makes accurate threshold estimation unlikely in awake patients. Cortical ERA tests are much less sensitive to muscle activity but are affected by mental arousal level, making them most suitable for alert adults and passively co-operative older children. ABR tests require short duration stimuli which carry restricted frequency-specific information and makes low frequency tests especially difficult whereas cortical tests can use longer, highly frequency-specific stimuli of any frequency, allowing an audiogram to be constructed, assuming one has the time and inclination to do so.
The following table summarises the main pros & cons of the two tests as implemented on a standard ERA system when testing adults or older children (manual collection, replication & manipulation of data):