The lowest or minimal level of a pure tone that an average human ear can detect in a quiet room is called the auditory threshold. This threshold level, however, can vary depending on the frequency of the tone, whether it is a low or high frequency. Since sound is a wave, the auditory threshold is truly measuring a change in pressure sensation in an individual’s ear. Audiologists are health care professionals who use specific tools to test a person’s hearing abilities and his or her auditory threshold. Certain tools are used for different age groups, particularly since infants and young children may not understand the directions to show that they hear a sound or tone.
Types of Auditory Tests
There are two methods to measure an individual’s absolute threshold of hearing: minimal audible field and minimal audible pressure tests. The main difference between these tests are that the minimal audible field tests both ears at the same time—binaural hearing—while minimal audible pressure tests one ear at a time—monaural hearing. In a minimal audible field test, the person sits in a sound booth (field) with stimuli being presented via loudspeakers. The person steps out of the booth and the level of sound is measured at the position of the person’s head. In minimal audible pressure test, the individual puts on headphones and stimuli are presented though the headphones. This process measures sound pressure in the person’s ear canal using a small probe microphone. Generally, minimal audible field thresholds are lower than the minimal audible pressure threshold because binaural hearing is more sensitive than monaural hearing. This could be due to the person with the headphones also hearing internal noises such as heartbeat or swallowing that could mask the pressure stimuli.
Classical Auditory Testing
To understand how the test is performed, the patient is told that a sound will be produced and how to respond when he or she hears the tone. In this yes/no paradigm, during each interval of the hearing test a sound is either present or absent. The individual then responds, stating whether he or she heard the stimulus. The hearing test continues with a predetermined sequence including a catch trial where no tone is presented.
The most common test for absolute threshold of hearing is the method of limits. In this paradigm, the tester controls the levels of stimuli but there are no catch trials. The tone progresses through multiple series of ascending or descending intensities. In the ascending trial run, the tone is presented well below the person’s expected auditory threshold. The tone is then slowly increased until the individual responds. The opposite occurs in the descending trial run. In this test the tone is well above the anticipated auditory threshold. When the person responds correctly to the stimulus, the tone is decreased by a specified amount and presented again. This paradigm continues until the individual no longer responds to the presented stimuli. After several ascending and descending trials, the person’s absolute hearing threshold is calculated as the average intensity between the last audible tone and the first inaudible level.
Patricia A. Bloomquist and Jennifer L. Hellier
See also: Auditory Hallucinations; Auditory Processing Disorder; Auditory System; Brainstem Auditory Evoked Potentials; Cochlea; Cochlear Implants; Vestibulocochlear Nerve
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Nave, R. (2016). Threshold of hearing. HyperPhysics at Georgia State University. Retrieved from http://hyperphysics.phy-astr.gsu.edu/hbase/sound/earcrv.html
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