Transcript Instrumentation

ABR measures

Absolute latency

Inter-peak latency

Wave amplitudes

Threshold of wave V

Wave morphology at higher and lower click rates
Late responses

Auditory middle latency responses (AMLR):
Latency: 15-60 ms
Site of origin: Areas in brainstem and cortex
Affected by state of individual

Auditory late responses (ALR): Latency
Latency: > 60 ms
Site of origin: Areas in cortex
Affected by state of individual
Example: P300, MMN
Behavioral tests of lesion

Used to differentiate cochlear/retrocochlear site of
lesion.

Mostly replaced by OAE and electrophysiological tests.

Examples of behavioral tests:

ABLB (Alternate binaural loudness balance)

SISI (Short increment sensitivity index)

Tone decay test
ABLB

Based on phenomenon of recruitment.

In normal hearing ears and hearing loss without
recruitment, loudness grows in both ears in the same
way. Equal loudness at equal sensation levels.

Recruitment: Abnormally rapid growth of loudness in the
poorer ear. Seen in cochlear hearing loss.

Decruitment: Loudness grows very slowly in the poorer
ear. Even very intense sounds may not be very loud.
Seen in auditory nerve lesions.
Growth of loudness
SISI

Aim: To detect a small increment ( 1 dB)
superimposed on a 20 dB SL tone.

Rationale: Because of abnormal loudness
growth, individuals with cochlear hearing loss
obtain high scores (are able to detect the
increment very well).

Normal hearing listeners and retrocochlear
hearing loss obtain poor SISI scores.
Tone decay


For sustained tones, threshold increases as the duration of the tone
increases.
Steps:
1.
Present tone at 20 dB SL
2.
As soon as patient signals that the tone is heard, start stopwatch.
3.
When patient stops hearing, then increase level by 5 dB without
interrupting it.
4.
Procedure continued till a) tone is heard for 60 s, b) tone is 30 dB
above starting level and patient cannot hear for 60 s at that level, or c)
audiometric limits have been reached.
Interpretation

Type I: Tone is heard for 60 s. Seen mostly in normal-hearing listeners,
conductive hearing loss.

Type II: As level is raised, tone decay reduces (tone is heard for longer and
longer durations). Strong indicator of cochlear hearing loss.

Type III: Even with increasing levels, tone decay still observed. Indicator of
auditory nerve lesions.