top of page

Understanding Special Tests in Audiology: Insights from Baranagar Speech & Hearing Clinic

When it comes to diagnosing and treating hearing disorders, precision and thoroughness are paramount. At Baranagar Speech & Hearing Clinic, a variety of specialized tests are employed to accurately identify the nature and location of auditory issues. These tests, which include Short Increment Sensitivity Index (SISI), Tone Decay Test (TDT), Alternate Binaural Loudness Balance Test (ABLB), and Monaural Loudness Balance Test (MLB), play a crucial role in distinguishing between cochlear lesions and retrocochlear lesions. This blog delves into these special tests, exploring their methodologies and significance in audiological assessments.

The Importance of Differentiating Cochlear and Retrocochlear Lesions

Cochlear lesions involve damage to the cochlea, the sensory organ responsible for converting sound waves into neural signals. Retrocochlear lesions, on the other hand, refer to issues beyond the cochlea, typically involving the auditory nerve or central auditory pathways. Accurate differentiation between these two types of lesions is essential because they require different diagnostic approaches and treatment plans. Specialized audiological tests are designed to pinpoint the exact nature of the hearing impairment, guiding effective intervention strategies.

Short Increment Sensitivity Index (SISI)

The Short Increment Sensitivity Index (SISI) test is a diagnostic tool used to detect cochlear lesions. This test evaluates a person’s ability to perceive small changes in sound intensity, which is often affected in cochlear pathologies.


During the SISI test, a continuous tone is presented at a level slightly above the individual’s hearing threshold. Small increments in intensity, usually around 1 dB, are introduced, and the patient is asked to indicate when they detect these increments.


Individuals with normal hearing or retrocochlear lesions typically struggle to perceive these small changes in intensity. However, those with cochlear lesions can often detect the increments, even at very small levels. A high score on the SISI test suggests a cochlear origin of hearing loss, providing valuable information for further diagnosis and treatment planning.

Tone Decay Test (TDT)

The Tone Decay Test (TDT) is designed to assess auditory fatigue, which can indicate the presence of retrocochlear lesions.


In this test, a continuous tone is presented at the hearing threshold level in one ear. The patient is instructed to signal as long as they hear the tone. If the tone becomes inaudible within 60 seconds, the intensity is increased by 5 dB, and the process is repeated.


Normal auditory systems or those with cochlear lesions can usually sustain the tone without significant decay. However, if the tone decays rapidly (within 60 seconds), it suggests a retrocochlear pathology. The TDT is particularly useful in identifying lesions affecting the auditory nerve or pathways, prompting further neurological evaluation.

Alternate Binaural Loudness Balance Test (ABLB)

The Alternate Binaural Loudness Balance Test (ABLB) is used to compare the loudness perception between the two ears, helping to identify asymmetrical hearing loss often associated with cochlear lesions.


During the ABLB test, tones of varying intensities are alternately presented to each ear. The patient is asked to compare the loudness of these tones, indicating when the loudness perception is equal in both ears.


In cases of cochlear lesions, loudness recruitment (an abnormal growth in perceived loudness) is common. This means that even a small increase in intensity can be perceived as a significant change in loudness. The ABLB test helps to quantify this phenomenon, distinguishing cochlear pathology from retrocochlear issues where loudness recruitment is less likely to occur.

Monaural Loudness Balance Test (MLB)

The Monaural Loudness Balance Test (MLB) focuses on assessing loudness perception within a single ear, providing further insights into cochlear function.


Similar to the ABLB, the MLB test involves presenting tones of different intensities to one ear and asking the patient to judge the loudness. The goal is to determine the point at which the patient perceives the loudness as balanced.


The MLB test helps identify loudness recruitment in one ear, supporting the diagnosis of cochlear lesions. By isolating the ear in question, audiologists can better understand the specific nature of the hearing loss, aiding in the development of targeted treatment plans.

Integrating Special Tests into Comprehensive Audiological Assessments

At Baranagar Speech & Hearing Clinic, these special tests are integrated into comprehensive audiological assessments. Each test provides unique insights into the auditory system, and when used together, they offer a detailed picture of the patient’s hearing health.

A Collaborative Approach

The success of these tests lies in their precise administration and interpretation by skilled audiologists. At Baranagar Speech & Hearing Clinic, audiologists work closely with patients, ensuring that the tests are conducted accurately and the results are interpreted in the context of each individual’s overall health and hearing profile.

Personalized Treatment Plans

The information gathered from these tests allows for the creation of personalised treatment plans. Whether the diagnosis points to a cochlear or retrocochlear lesion, the clinic’s audiologists can tailor interventions to address the specific needs of the patient. This might include hearing aids, cochlear implants, auditory training, or referrals for further medical evaluation.


Specialised audiological tests such as the Short Increment Sensitivity Index (SISI), Tone Decay Test (TDT), Alternate Binaural Loudness Balance Test (ABLB), and Monaural Loudness Balance Test (MLB) are invaluable tools in the accurate diagnosis and treatment of hearing disorders. By distinguishing between cochlear and retrocochlear lesions, these tests enable audiologists to develop targeted and effective treatment plans.

At Baranagar Speech & Hearing Clinic, the integration of these tests into comprehensive audiological assessments ensures that patients receive the highest standard of care. With a commitment to precision and personalised treatment, the clinic stands at the forefront of audiological services in Kolkata, helping individuals achieve better hearing health and an improved quality of life.

0 views0 comments


bottom of page