Tone Decay Test (TDT)
The tone decay test (also known as the threshold tone decay test or TTDT) is used to detect and measure auditory fatigue.
In people with normal hearing, a tone whose intensity is only slightly above their absolute threshold of hearing can be heard continuously for 60 seconds. The tone decay test produces a measure of the “decibels of decay”, i.e. the number of decibelsabove the patient’s absolute threshold of hearing that are required for the tone to be heard for 60 seconds. A decay of between 15 and 20 decibels is indicative of cochlear hearing loss and the decay more than 25 decibels is indicative of damage to the vestibulocochlear nerve.

SHORT INCREMENT SENSITIVITY INDEX TEST (SISI)
The SISI test is still widely used to determine cochlear pathology in patients. This test is based on a phenomenon known as recruitment (abnormal loudness growth).

Clinical Procedure for SISI

1. The patient will be made to relax on a reclining chair, with earphones attached.

2. A pure tone at an intensity of 20dB will be passed into the ear.

3. A small increase in intensity is superimposed upon the steady state tone at periodic intervals. The size of intensity increment varies form 5dB-1dB.

4. The ability to detect the 1 dB increments is present only in patients with cochlear pathology and is absent in patients with normal hearing or with a conductive hearing loss.

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