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).