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D

Decibel - measurement of the intensity or loudness of a sound. 

Developmental level/age - the age at which a child acquires specific skills

Difference Limens (DL) - Many psychological experiments in the field of sensation and perception have been performed to measure difference limens or limena. A difference limen (DL) in any sensory process is defined as a just noticeable difference (JND) in whatever aspect of the sensation is under investigation. Thus, so far as hearing is concerned, the DL for frequency is the amount of change in frequency required to produce a JND pitch, or the DL for intensity is the amount of change in intensity required to produce a JND in loudness. Most of the work with DL's in clinical hearing tests has been concerned with measuring the size of the DL for intensity. 

Digital Hearing Aid - Hearing aids that use a digital circuit to analyze and process sound. These aids are available in ITC (In-the-canal), ITE (In-the-ear), CIC (Completely in the Canal) and BTE (Behind-the-ear) models.

Direct Audio Input - direct input of sound into a hearing aid by means of a hard-wired connection between the hearing aid and an assistive listening device or other sound source

Dispenser - A person trained to fit and dispense hearing systems.

Down's Syndrome - (J.L.H. Down, English physician, 1828-1896) congenital abnormality with a wide variety of symptoms including mental retardation, mild to severe; caused by the representation of chromosome 21 three times, instead of twice, in some or all cells; also called chromosome 21-trisomy syndrome or mongolism. This syndrome is also characterized by varying degrees of hearing loss, and speech impairment, as well as other physical signs.

Dry-aid Kit - a package of products, including a pouch of silica gel which is used to reduce moisture in hearing aids 

E

Ear (auris)- organ of hearing and balance that is divided into:

• 1. The external ear includes the sound-collecting visible portion (auricle or pinna), the outer ear canal (external auditory meatus), and the outer surface of the eardrum (tympanum).
• 2. The middle ear includes the inner surface of the eardrum, the ossicular chain (hammer, anvil and stirrup - or malleus, incus, and stapes), the eustachian tube, and the outer surface of the oval and round windows, and the cochlea.
• 3. The inner ear includes the vestibule, the semi-circular canals, the inner surface of the oval
  and round windows, and the cochlea.

Earache - ear pain. Any ache or pain arising in the ear. Technically it may be called otalgia or otodynia.

Ear Canal - see External Auditory Meatus

Eardrum - (tympanic membrane) A thin layer of skin at the end of the external ear canal.

Earhook - the portion of a behind-the-ear hearing aid that connects the case to the earmold tube and hooks over the outer ear

Earmold - a custom fit device that attaches to a behind-the-ear (BTE) hearing aid to deliver sound from the aid to the ear; other types of earmolds can be made as custom swim plugs (to block out water) or as noise protection ear plugs

Ear Plugs - a device that goes in the ear or covers the ear designed to keep noise out, thereby protecting the hearing of the individual.

Ear Specialist - commonly accepted name for a medical ear specialist is otologist. He or she may also be known as an aural surgeon aurist. Other medical specialists especially interested in ears are variously known as otolaryngologists or otorhinolaryngologists - (oto) ear, (rhino) nose, (laryngo) throat specialists.

Ear-specific Testing - hearing test designed to derive independent thresholds by testing each ear separately

Ear Trumpet - a device with a large opening at one end designed to gather sound waves and direct them through a smaller opening into the outer ear canal.

Ear Wax - wax in the external ear; see also cerumen

Echolalia - involuntary repetition of words or phrases just spoken by someone else. Also known as echologia, echophasia, echophrasia, echo speech and mimic speech.

Effusion - discharge of fluid into a body cavity, such as the middle ear, as a result of inflammation

Eighth Nerve - Cranial Nerve VIII; consists of the suditory nerve and vestibular nerves. The nerve that transmits messages from the inner ear to the brain.

E.N.T. - Otologists, Otolaryngolists and E.N.T. physicians are medical doctors trained in diagnosing and treating diseases of the ear, and in identifying types of hearing loss that respond to medical or surgical treatment. Some offices may have a hearing aid specialist or dispensing audiologist on staff for patients who can benefit from the use of hearing aids.

Embryo - developing fetus from about two weeks after conception to the end of the seventh or eighth week

Erythroblastosis Fetalis - This is a disease with oxygen deficiency (see anoxia) in the blood of the fetus caused by Rh incompatibility in the parents of the unborn baby. Rh incompatibility; when the mother and her child have incompatible blood groups. This occurs when the mother's blood type is Rh negative and the father's is Rh positive, resulting in an Rh positive child. Rh incompatibility is a serious disease which has greater consequences with each pregnancy.

Eustachian Tube - (Bartolomeo Estachio, Italian anatomist, 1510-1574) A tube approximately 1 1/2 inches (36 mm) long connecting the middle ear cavity and the nasopharynx (back of the throat). It has a diameter of 1/8 " to 1/4 " (3 mm to 6 mm) It can be opened by coughing or swallowing, though it is normally closed. The occasional opening of the Eustachian tube is necessary to equalize the air pressure in the middle earcavity with outside air. Also called: auditory tube (tuba auditiva) 

External Auditory Meatus (Canal) or External Auditory Canal - the portion of the auditory system that extends (approximately 2.3 cm to 2.9 cm) from the opening of the ear to the eardrum; also called the ear canal. The auditory canal is the channel through which the sounds are led from the ear outside to the middle ear. It functions to reinforce sound and provide protection for the eardrum.

Eyeglass -Amplification devices in the form of eyeglass frames are available. These instruments are designed for wearers who wear eyeglasses and for whom conventional hearing instruments are not practical.

F

Feedback - a high-pitch squealing or whistling sound that occurs when amplified sound is re-amplified usually due to a leak from an aid or earmold that does not fit properly

Fetus - an unborn baby

Frequency - the number of complete oscillations per unit of time; with sound, frequency is the number of cycles per second expressed in Hertz (Hz); see " pitch " For example, 256 HZ has the same pitch as middle C on the piano. Doubling this produces a tone one octave higher; if it is halved the tone will be one octave lower. Pitch is the psychological response to frequency.

Frequency modulation (FM) system - an assistive listening device used especially in schools to reduce the interference of background noise. It transmits the speaker's voice via a microphone to a small receiver

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