What do Otoacoustic Emissions (OAEs) sound like and are they prompted by environmental sounds?

Understanding Otoacoustic Emissions (OAEs)

Otoacoustic emissions (OAEs) are acoustic signals generated within the cochlea that travel in a reverse direction through the middle ear and tympanic membrane out to the ear canal, and are not sounds that a person can hear themselves. 1

What OAEs Are and How They're Generated

OAEs are physiological phenomena that originate from the cochlea's sensory hair cells, specifically the outer hair cells, as they respond to auditory stimulation:

• They are caused by the motion of the cochlea's sensory hair cells as they energetically respond to sound 2
• OAEs are recorded using a sensitive microphone placed in the ear canal 1
• They are generated in response to an auditory stimulus, typically clicks or tone bursts 1
• OAEs reflect the status of the peripheral auditory system extending to the cochlear outer hair cells 1

Types of OAEs and Their Measurement

There are two primary mechanisms by which OAEs are generated:

1. Nonlinear distortion: Generated through nonlinear cochlear processes 3
2. Linear reflection: Produced through linear reflection mechanisms 3

Clinically measured OAEs include:

• Evoked OAEs: Generated in response to acoustic stimuli
  • Transient-evoked OAEs (TEOAEs): Response to clicks or tone bursts
  • Distortion-product OAEs (DPOAEs): Response to two simultaneous tones
• Spontaneous OAEs: Occur without external stimulation

OAEs and Environmental Sounds

OAEs are not sounds that a person hears in response to environmental sounds. Important distinctions:

• OAEs are not perceptible to the person generating them 2
• They require specialized equipment (a sensitive microphone) to detect 1
• OAEs are evoked during testing using specific stimuli (clicks or tone bursts) delivered through a probe placed in the ear canal 1
• They are not a subjective experience but rather an objective physiological response 2

Clinical Applications of OAEs

OAEs have several important clinical applications:

• Newborn hearing screening: Provides a quick, non-invasive screening test for hearing function 4
• Monitoring cochlear function: Used to detect early changes in hearing due to ototoxicity or noise exposure 1
• Differential diagnosis: Helps distinguish between cochlear and neural hearing disorders 1

Limitations and Considerations

OAEs have specific limitations that affect their interpretation:

• They only assess the peripheral auditory system up to the outer hair cells 1
• OAEs cannot detect neural (eighth nerve or auditory brainstem pathway) dysfunction 1
• Middle ear conditions (like fluid or effusion) can affect OAE measurement even when cochlear function is normal 5
• OAEs may be absent in the presence of even mild hearing loss 1

Key Points for Medical Providers

When interpreting OAE results:

• OAEs provide information about cochlear health but not about central auditory processing
• A "pass" on OAE testing indicates normal outer hair cell function but does not rule out neural hearing disorders
• OAEs are highly sensitive to middle ear conditions, which can result in false "fail" results
• For complete hearing assessment, OAEs should be used in conjunction with other audiological tests like ABR

In summary, OAEs are physiological responses generated by the cochlea that require specialized equipment to detect and are not sounds that individuals can hear themselves in response to environmental stimuli.