Short Increment Sensitivity Index (SISI)
What is the SISI test?
SISI is a test of a person’s ability to recognize 1 dB increases in intensity during a series of bursts of pure tones presented 20 dB above the pure tone threshold for the test frequency. You can use the SISI test to differentiate between cochlear and retrocochlear disorders, as a patient with a cochlear disorder will be able to perceive the increments of 1 dB, whereas a patient with a retrocochlear disorder will not.
How to do the SISI test
The following steps will outline how to do the test using a two-channel audiometer.
You will also need headphones or insert phones and a response button.
Figure 1 shows what the test screen looks like in our software.
Figure 1: SISI test screen.
Step 1
Select a tone or warble stimulus in channel 1.
If you suspect cross hearing, then you should present masking in channel 2.
Step 2
Select the desired test frequency and set the input level 20 dB above threshold.
Step 3
In the most common type of SISI test, the incremental steps are 1 dB.
You can change these to 0, 2, or 5 dB.
0 dB is for when you are uncertain about your patient’s responses, while 2 or 5 dB are good for trialing that your patient understands the test procedure.
Step 4
Before testing, explain to your patient that he/she will now hear a series of tones.
Instruct your patient to push the response button if they think the loudness of the tone changes.
Step 5
The system will automatically count the number of reactions from the patient.
Note that the system needs 20 presentations to calculate a SISI score.
Repeat the test for all desired test frequencies.
How to interpret SISI results
Expanding upon the previous definition, SISI is a measure of one’s ability to tell the difference between the loudness of sound.
The test takes advantage of the increased sensitivity to loudness changes in patients with cochlear losses, which is due to cochlear recruitment.
In someone with a retrocochlear loss, we do not expect the same degree cochlear recruitment, meaning they would be less sensitive to changes in the loudness of sound.
The score is a percentage, which expresses the number of 1 dB increments the patient detected out of the twenty in total, multiplied by five:
- 70-100% correct = high (cochlear loss)
- 20-70% correct = inconclusive
- <20% = low (retrocochlear loss)
