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 Example: P300, MMN 2

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: Present tone at 20 dB SL As soon as patient signals that the tone is heard, start stopwatch. When patient stops hearing, then increase level by 5 dB without interrupting it. 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.