Neurootological Tests

SPEECH AUDIOMETRY

This test measures the percentage of words correctly interpreted as a function of the intensity of presentation and indicates the usefulness of hearing. The graph shows how different types of hearing loss can be differentiated.

Normal

Conductive

Pretaped words

Pretaped words

Percentage of words correct
Cochlear Retrocochlear

Intensity

STAPEDIAL REFLEX DECAY

Afferent pathway VIII nerve \

Afferent pathway VIII nerve \

Impedence of tympanic membrane monitored with a probe tone

Activating tone stimulus

An intense acoustic stimulus causes reflex contraction of the stapedius muscle. This in turn causes reduced compliance (increased impedence) of the tympanic membrane.

Activating tone stimulus

Impedence of tympanic membrane monitored with a probe tone

Rapid decay of the reflex response suggests a lesion of the auditory nerve

Efferent pathway via both VII nerves (nerve to stapedius)

AUDITORY BRAINSTEM EVOKED POTENTIAL

Pulse generator

Signal

ms

averager

I

Amplifier

Masking noise

IV V

' Mastoid electrode (reference)

IV V

Masking noise

Averaging techniques (page 52) permit the recording and analysis of small electrical potentials evoked in response to auditory stimuli. Activity in the first 10 ms provides information about the VIII nerve and nucleus (waves I and II) and the pons and midbrain (waves III - V). Lesions of the VIII nerve diminish the amplitude and/or the latency of wave I or II and increase the wave I to V interpeak latency. In comparison, cochlear lesions seldom affect either wave pattern or latency.

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