tential cues and neural processing strategies have been suggested as ways in which the sources of many sounds can be processed and segregated in a complex, multisource acoustic environment. People with hearing loss often remark that they have problems in noisy situations, such as at a cocktail party, implying that they are not able to determine the auditory scene as well as people without hearing loss.

Thus, listeners with normal hearing can use many potential cues to determine many of the sources of sounds in the workplace, even when the sounds from the sources overlap in time and perhaps in space.

CAUSES OF HEARING LOSS

In general, hearing loss can be caused by heredity (genetics), aging (presbycusis), loud sound exposure, diseases and infections, trauma (accidents), or ototoxic drugs (drugs and chemicals that are poisonous to auditory structures). Hearing loss can categorized into the following ranges based on PTAs (PTA 512):

  • slight (16-25 dB hearing loss)

  • mild (26-40 dB hearing loss)

  • moderate (41-55 dB hearing loss)

  • moderately severe (56-70 dB hearing loss)

  • severe (71-90 dB hearing loss)

  • profound (greater than 90 dB hearing loss)

The loss can be caused by damage to any part of the auditory pathway. Three major types of hearing loss have been defined: conductive, sensorineural, and mixed. Conductive hearing loss refers to damage to the conductive system of the ear—that is, the ear canal, tympanic membrane (eardrum), and ossicles (middle ear bones)—and can include fluid filling the middle ear space. Sensorineural hearing loss indicates a problem in the inner ear, auditory nerve, or higher auditory centers in the brainstem and temporal lobe. Mixed hearing loss designates that the hearing loss has both a conductive and sensorineural component. Treatments for hearing loss involve surgery, hearing aids of various types, cochlear prostheses, medication, and various forms of habilitation and rehabilitation.

Conductive Hearing Loss

If a problem arises in the external or middle ear, a conductive hearing loss occurs that is largely due to the outer and middle ear’s no longer being able to overcome the loss in sound transmission from the outer to



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