ABR measuresABR measures

Absolute latencyAbsolute latency

Inter-peak latencyInter-peak latency

Wave amplitudesWave amplitudes

Threshold of wave VThreshold of wave V

Wave morphology at higher and lower Wave morphology at higher and lower click ratesclick rates

Late responsesLate responses

Auditory middle latency responses (AMLR): Auditory middle latency responses (AMLR):

Latency: 15-60 ms Latency: 15-60 ms

Site of origin: Areas in brainstem and cortexSite of origin: Areas in brainstem and cortex

Affected by state of individualAffected by state of individual

Auditory late responses (ALR): LatencyAuditory late responses (ALR): Latency

Latency: > 60 ms Latency: > 60 ms

Site of origin: Areas in cortexSite of origin: Areas in cortex

Affected by state of individualAffected by state of individual

Example: P300, MMNExample: P300, MMN

Behavioral tests of lesionBehavioral tests of lesion

Used to differentiate cochlear/retrocochlear site Used to differentiate cochlear/retrocochlear site of lesion.of lesion.

Mostly replaced by OAE and electrophysiological Mostly replaced by OAE and electrophysiological tests.tests.

Examples of behavioral tests:Examples of behavioral tests:

ABLB (Alternate binaural loudness balance)ABLB (Alternate binaural loudness balance)

SISI (Short increment sensitivity index)SISI (Short increment sensitivity index)

Tone decay testTone decay test

ABLBABLB

Based on phenomenon of recruitment.Based on phenomenon of recruitment.

In normal hearing ears and hearing loss without In normal hearing ears and hearing loss without recruitment, loudness grows in both ears in the recruitment, loudness grows in both ears in the same way. same way. Equal loudness at equal Equal loudness at equal sensation sensation levelslevels..

Recruitment: Abnormally rapid growth of loudness Recruitment: Abnormally rapid growth of loudness in the poorer ear. Seen in cochlear hearing loss. in the poorer ear. Seen in cochlear hearing loss.

Decruitment: Loudness grows very slowly in the Decruitment: Loudness grows very slowly in the poorer ear. Even very intense sounds may not be poorer ear. Even very intense sounds may not be very loud. Seen in auditory nerve lesions.very loud. Seen in auditory nerve lesions.

Growth of loudnessGrowth of loudness

SISISISI

Aim: To detect a small increment ( 1 dB) Aim: To detect a small increment ( 1 dB) superimposed on a 20 dB superimposed on a 20 dB SLSL tone.tone.

Rationale: Because of abnormal loudness Rationale: Because of abnormal loudness growth, individuals with cochlear hearing growth, individuals with cochlear hearing loss obtain high scores (are able to detect loss obtain high scores (are able to detect the increment very well). the increment very well).

Normal hearing listeners and retrocochlear Normal hearing listeners and retrocochlear hearing loss obtain poor SISI scores.hearing loss obtain poor SISI scores.

Tone decayTone decay

For sustained tones, threshold increases as the duration of the tone For sustained tones, threshold increases as the duration of the tone increases.increases.

Steps: Steps: 1.1. Present tone at 20 dB SLPresent tone at 20 dB SL2.2. As soon as patient signals that the tone is heard, start stopwatch.As soon as patient signals that the tone is heard, start stopwatch.3.3. When patient stops hearing, then increase level by 5 dB without When patient stops hearing, then increase level by 5 dB without

interrupting it.interrupting it.4.4. Procedure continued till a) tone is heard for 60 s, b) tone is 30 dB 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 above starting level and patient cannot hear for 60 s at that level, or c) audiometric limits have been reached.level, or c) audiometric limits have been reached.

InterpretationInterpretation

Type I: Tone is heard for 60 s. Seen mostly in normal-hearing Type I: Tone is heard for 60 s. Seen mostly in normal-hearing listeners, conductive hearing loss.listeners, conductive hearing loss.

Type II: As level is raised, tone decay reduces (tone is heard for Type II: As level is raised, tone decay reduces (tone is heard for longer and longer durations). Strong indicator of cochlear hearing longer and longer durations). Strong indicator of cochlear hearing loss.loss.

Type III: Even with increasing levels, tone decay still observed. Type III: Even with increasing levels, tone decay still observed. Indicator of auditory nerve lesions.Indicator of auditory nerve lesions.