In the course of the test, an audiometer is used to play over-loud volume jumps in the ears of the patient, which are either recognized by the test person or remain unrecognized. The evaluated percentage of detected volume increases helps to assess whether positive or negative recruitment exists.
What is the SISI test?The test belongs to the group of over-threshold hearing tests, as the patient is offered volume fluctuations above the hearing threshold.
SISI stands for "short increment sensitivity index" and is the name of a subjective and audiometric test procedure for ear, nose and throat medicine. The test belongs to the group of over-threshold hearing tests, as the patient is offered volume fluctuations above the hearing threshold. Above all, the method has a relevance for recruitment, ie a psychoacoustic phenomenon in inner ear diseases.
With the SISI, conclusions about the cause of sensorineural hearing loss can be drawn. The test results can be used to diagnose positive or negative recruitment. The test was developed in 1959 by James Jerger and colleagues. At the time, the basis of this development was the Lüscher test, which, although based on the same principles, is associated with considerably more effort for the patients and the test personnel.
Function, effect & goals
In the SISI, intensity differences in the level range are measured by the excitation of hair cells in the inner ear. The basis for the test is the assumption that hearing-impaired people perceive small level fluctuations as clearly as hearing-healthy people. To perform the SISI, an audiometer is required. Headphones are used to play sounds to the patient at a supralonic level.
In addition to many hospitals, such an audiometer also has the most ENT latches and praxes. As a rule, the SISI is only performed on patients who suffer from a hearing impairment of at least 40 dB. At lower hearing thresholds, the test is not applied because the test procedure then lacks informative value. The threshold of 60 dB should not be exceeded during the entire test process. Since the test is a subjective audiometric test procedure, the patient's cooperation during the SISI is explicitly required and is even crucial for the reliability of the results.
During the course of the test, the test person is given earbuds of various levels on the earphones, which become louder and louder by tiny dB jumps. The patient is prompted to comment on recognized db jumps. The test is opened by a test tone level that is around 20 dB above the individual hearing threshold. This test tone level is regularly increased for a short duration. In general, the time interval between the volume changes is around five seconds.
The amplitude of the intensity change is normally one dB each. The duration of the individual sound amplifications is always one second. The patient indicates after each change in the sound intensity whether he has detected a jump in the level. At the beginning of audiometry, the jump for him is usually clearly visible. Often loses towards the end of the investigation but the recognizability. The data collected during the investigation will be documented during the SISI and later evaluated by recruitment staff. For normal hearing, a level change of one dB can not be detected at 20 dB above the threshold of hearing.
If, on the other hand, there is cochlear sensorineural hearing loss, then the patient will also detect volume changes by one dB, which is undoubtedly 20 dB above the threshold of hearing. On the other hand, if retrocochlear causes are present for sensorineural hearing loss, such as damage to the auditory nerve, the intensity changes in the SISI test are not recognized.
The evaluated test result corresponds to the percentage of detected volume changes and serves to diagnose the recruitment. Values between 60 and 100 percent are associated with a positive recruitment. For values between 0 and 15 percent, there is negative recruitment. In the test range from 0 to 30 percent, there is therefore no cochlear hearing loss with high certainty. In the range between 70 and 100 percent, on the other hand, cochlear deafness can be assumed to be very probable.
Risks, side effects & dangers
The SISI is inextricably linked to the Lüscher test, in which James Jerger was officially oriented in the development. As with the Lüscher method, the SISI also focuses on the increased detectability of fluctuations in the sound intensity that patients have cochlear sensorineural hearing loss with respect to normal hearing.
Ultimately, the SISI corresponds to a methodological simplification of the Lüscher test procedure and has made the basis of the Lüschner test applicable only on a large scale. The SISI is therefore associated with no great effort, nor with risks or side effects for the patient. Nevertheless, the SISI is generally not applied to infants or people with intellectual disabilities.
Nor is the subjective test suitable for unwilling test persons. Since the cooperation of the patient is crucial for the accuracy of the data collected, the patient must be able to understand the test procedure and, in addition, be willing to behave. However, the results of the SISI are not always meaningful even for willing patients. For example, in the transition range between 15% and 60% of detected changes in volume, it is not possible to make a clear statement as to recruitment or the likelihood of hearing impairment.