Types of Hearing Tests — Subjective and Objective (OAE, ABR, ASSR, COR)

1. How the exam asks about it

The training curriculum for sign-language volunteers that candidates for the National Unified Examination study (Ministry of Health, Labour and Welfare notice of 26 June 2023) covers how the ear works, hearing aids and cochlear implants under basic knowledge of hearing impairment, but does not list types of hearing tests. This article is aimed at candidates for the certified interpreter exam.

2. Subjective and objective tests

Hearing tests fall into two broad groups.

• Subjective tests: judged from the person’s response or behaviour — raising a hand, pressing a button or turning toward the sound when they hear it
• Objective tests: a machine records the response of the ear or brain, without the person having to answer

Objective tests work for sleeping babies and for people who find it hard to respond. Japan’s certification guidelines also require “an objective hearing test such as the auditory brainstem response” when grade 2 is newly diagnosed for someone without a certificate.

The other way to look at it is how far along the ear each test reaches. Sound passes through the outer and middle ear, is turned into an electrical signal by the hair cells of the inner ear, and travels along the auditory nerve to the brainstem and brain. Tests differ in how far along that path they examine (Figure 1).

• SubjectiveTests where the person responds: to the brain (up to noticing “I heard that”)
• ObjectiveOAE: to the inner ear
• ObjectiveABR, ASSR: to the brainstem

When OAE is normal but ABR shows no response, the cause is thought to lie beyond the inner ear, between the auditory nerve and the brainstem.

3. Tests where the person respondsSubjective

Standard pure-tone audiometrySubjective

Pure tones are played through headphones frequency by frequency, the person signals when they hear one, and the level at which hearing begins is measured. Results go on an audiogram. There is also bone conduction, with a vibrator on the bone behind the ear; the gap between air and bone conduction tells conductive from sensorineural loss. See the audiogram article for details.

Speech audiometrySubjective

This tests how well speech is understood, not how loud a sound must be. Under Japan’s certification criteria, single-syllable test words are presented at a normal speaking level and the percentage correctly heard is the “speech discrimination score.” Grade 4 of the disability certificate has a criterion of 50% or less on this score.

Tests for infants (BOA, COR, play audiometry)Subjective

For children too young to wear headphones and signal, tests that watch behaviour are used.

COR and play audiometry use behaviour, so they count as subjective tests.

4. Tests where a machine records the responseObjective

TympanometryObjective

A thin tube in the ear canal changes the air pressure to examine the middle ear: middle-ear pressure, whether fluid has collected, and how well the ossicles move. It helps find otitis media with effusion and ossicle problems.

OAE (otoacoustic emissions)Objective

When sound goes in, the cochlea of the inner ear sends back a very faint sound, which a probe in the ear canal records. OAE tests the function of the cochlea’s outer hair cells. It is quick, but may show no response when the ear canal is narrow or the middle ear holds fluid.

Problems beyond the inner ear — the auditory nerve — cannot be found with OAE. Kanagawa Prefecture’s newborn screening guide says OAE “cannot detect problems in the auditory nerve and other parts central to the inner ear” (my translation).

ABR (auditory brainstem response)Objective

Electrodes on the head record the electrical response from the auditory nerve to the brainstem while the person sleeps and hears sounds. Clicks are the usual stimulus, and the result is said to reflect hearing mainly around 2000–4000 Hz. It can be done from just after birth.

Automated ABR, used in newborn screening, is a device developed for testing newborns. It checks the brainwave response to sounds about as quiet as a whisper, and gives a result of pass (response present) or refer (retest needed).

ASSR (auditory steady-state response)Objective

Like ABR, this is an objective test that records the brain’s electrical response to sound. Unlike ABR, it can estimate hearing frequency by frequency at 500, 1000, 2000 and 4000 Hz, so it examines the frequencies needed for speech in detail. It takes 30 minutes to an hour during sleep.

5. Newborn hearing screening

Babies have a hearing screening at the maternity unit soon after birth. The national notice on newborn hearing screening sets out this timing (Ministry of Health, Labour and Welfare, revised notice of 28 December 2017).

• First test by about day 3; if referred, a confirmation test by about one week
• Diagnostic tests by about 3 months at the latest
• Early support for children who need it should start by about 6 months at the latest

The October 2023 revision (Children and Families Agency) states that the first and confirmation tests should preferably use automated ABR. The reason given is auditory neuropathy spectrum disorder (ANSD). In ANSD the inner ear works normally or nearly so, so OAE gives a pass, while the auditory nerve does not, so automated ABR gives a refer.

The same revision recommends that, when the confirmation test is a refer, a test for congenital cytomegalovirus (CMV) infection be done within three weeks of birth. It is a urine test, covered by health insurance within the first three weeks.

6. Points to check before the exam

Closing

Hearing-test names are mostly abbreviations, and several look alike. Sorting them two ways — whether the person responds or a machine records, and how far along the ear the test reaches — makes the answer choices easier to narrow down.

To experience a simulation of hearing loss, try these learning tools on our site (in Japanese).

The way I have organised this is one way of looking at it. How tests are done and the age guidelines can differ by clinic and region. If you were taught differently, or you think a piece of this is off, I would be glad to hear it through the contact form (the article name is filled in for you).