Short Increment Sensitivity Index (SISI)

Short Increment Sensitivity Index (SISI) is based on the phenomenon of abnormal growth in loudness perception often seen in cochlear pathologies. Jerger, Shedd, and Harford observed that many ears with a hearing loss due to abnormal cochlear function appear to have extremely keen discrimination for small changes in tonal intensity. They defined a simple task, the SISI, to help in differentiating cochlear from retrocochlear disorders.

A continuous tone is presented to the patient, usually at 20 dB SL (Sensitivity Level), with an occasional 1 dB intensity increment. The patient is asked to respond each time he or she hears the very small increase. Patients with a cochlear pathology, who experience abnormal loudness growth, are more likely to perceive the small, 1 dB loudness increment, whereas patients with retrocohlear or central pathology will likely not hear the change.

With the SISI, a training session is conducted prior to test administration.