One of the simplest and most basic test for assessing the hearing of a person is to do a PTA- a Pure Tone Audiogram.

A Pure Tone audiogram is a simple graph that plots the frequency in the X-axis and the amplitude (volume) at which the sound is heard in the Y-axis. 

The test is carried out using an Audiometer and ear probes and headphones for hearing, including a call button to indicate a response.

The set-up

The test is ideally performed in the following manner

  • Two-room set up-the tester and the tested  separated by a glass window 
  • Soundproof room - Since ambient noise interferes with the test results
  • Calibration- The Audiometer, as well as the transducers, must be regularly calibrated and checked for accuracy

Modes Of Stimulation

The sound pathway is stimulated in two different ways - 

1. AIR CONDUCTION- (AC) Sound signal is given by headphones - either above the ears - supra-aural, or else inside the ear canal - insert earphones. 

Air Conduction checks the integrity of the entire hearing pathway from the external ear to the brain. 

2. BONE CONDUCTION - (BC) Sound signal is given by transducers that are placed on the mastoid bone behind the ears. 

Bone Conduction checks the integrity of the Cochlea and beyond, including the Acoustic Nerve (the nerve of hearing).

One ear is tested at a time, one frequency at a time.

TYPES OF HEARING LOSS

Hearing losses are typically and commonly of three types

1. Conductive Hearing Loss - BC is normal, AC is depressed 

2. SNHL- Sensorineural Hearing Loss - BC is depressed

3. Mixed Hearing Loss - when there is a pathology in the conductive as well as neural mechanism- as in patients with a long-standing ear infection- both BC and AC are depressed and there is a gap between the two.

DEGREE OF HEARING LOSS


Interpretations

It must be understood that a PTA  is the basic preliminary test to check for hearing ability.

There are many other tests that are subsequently carried out, including

  • Speech Audiometry - to check for ability to understand speech
  • ABLB Alternate Binaural Loudness Balance - 
  • SISI - Short increment Sensitivity Index - check for ability to check for a small increase in sound.

The last two determine the level of the hearing loss - whether at the Cochlear or Retrocochlear level.

Other tests including BERA, ASSR as well as radiological investigations may be ordered to come to a proper diagnosis as well as for treatment planning.