Audiometry (electric response)

This encompasses a number of techniques in which surface recording electrodes placed on the head, together with computer averaging techniques, are used to study the response of different auditory pathways to sound. The key is to effectively block out interference from background electrical activity in the brain by presenting a barrage of time-locked, discrete sounds, rather than a single sound.

The techniques most commonly used are:

• electrocochleography (ECochG)
  • assesses cochlea response to sound
  • employed in the diagnosis of endolymphatic hydrops in Meniere's disease
    
    
• auditory brainstem responses (ABR)
  • measures the time taken for an impulse to pass from the cochlea to the brainstem
  • useful as a screen for acoustic neuromata because conduction delay may occur while the tumour is small
  • useful as an objective test of hearing in babies and young children
    
    
• auditory cortical responses
  • assesses electrical activity in the auditory cortex in response to sound
  • suitable when conventional audiometry is impractical, e.g. an incapable or malingering patient