TONE DECAY TEST: PROCEDURE OF TDT
1. Carhart's method: The most popular method is thr Carhart's method of TDT. The process is as follow:-
Step1: A pure tone stimulus is presented 10dBbelow threshold and raised in 5dB steps till the patient respond.
Step2: As soon as the patient respond a stop watch is started , the tone being constantly maintained .
Step3: the patient is asked to indicate as soon as he fail to hear the tone, and the time on the stop - watch is followed . if the test is terminated. if the patient stops hearing the tone before on minute is completed , then time is noted and immediately step 4 is started.
Step4: The tone is immediately raised by 5dB without giving any time gap, the stop watch is brought back to zero and started again. if the patient hear the tone of full one minute then the test is terminated, but if the patient stops hearing before one minute then the time is recorded and step 4 is repeated all over again.
if it is found that the tone has beenraised by 30dB above threshold i.e 3-0dB(SL), and yet the patient is unable to hear thetone for one full minute , the test is not continued any further.
The sound level by 30dB above hearing threshold the patient does not hear the sound for one full minute , then the test of TD is recorder as very strongly positive.
