Abdominal aponeurosis: Broad flat tendon covering the abdomen and serving as an anchor for abdominal muscles.

Acoustic (VIII) nerve: The auditory nerve running from the base of the cochlea to the brain stem and upward to end at the auditory cortex in the temporal lobe of the brain.

Acoustic feedback: The whistling sound that is created when the signal leaving the receiver of a hearing aid leaks back into the microphone and is reamplified.

Acoustic gain: The difference, in decibels, between the intensity of the input signal and the intensity of the output signal in a hearing aid.

Acoustic immittance: The sound that the eardrum reflects during tympanometric testing.

Acoustic impedance: The total opposition to the flow of acoustic energy (as in the plane of the eardrum membrane). It consists of mass, stiffness, and frictional resistance and is influenced by frequency.

Acoustic neuritis: Inflammatory or degenerative lesions of the auditory nerve.

Acoustic neuroma: A tumor on the nerve sheath that may result in vertigo, tinnitus (ringing in the ear), and hearing loss.

Acoustic reflex arc: The path of an acoustic stimulus that ascends from the outer ear to the brainstem and then descends via the facial nerves on both sides of the head to innervate the stapedial muscles in both middle ears.

Acoustic reflex decay: A decrease in the magnitude of the middle-ear reflex that occurs with constant acoustic stimulation.

Acoustic reflex threshold (ART): The lowest intensity at which a stimulus can produce the acoustic reflex.

Acoustic reflex Contraction: of one or both of the middle-ear muscles in response to an intense sound.

Acoustic trauma notch: A precipitous increase in hearing loss in the 3000 to 6000 Hz range, with recovery of hearing function at higher frequencies. It is usually, but not exclusively, associated with patients with noise-induced hearing loss.

Acquired immune deficiency syndrome (AIDS): See Human immunodeficiency virus.

Acquired: Occurring after birth.

Action potential (AP): A change in voltage measured on the surface of a neuron when it fires.

Active electrode: The electrode used in testing auditory evoked potentials in conjunction with a reference electrode. It is placed on an area of the scalp, such as the vertex, where electrical activity is high. The potential difference between these electrodes is amplified, thus canceling out unwanted signals.

Acute laryngitis: Temporary swelling of the vocal folds, resulting in a hoarse voice quality.

Acute A: condition characterized by rapid onset, frequently of short duration.

Addition: In articulation, the insertion of a phoneme that is not part of the word.

Aditus ad antrum: A space in the middle ear containing the head of the malleus and the greater part of the incus. It communicates upward and backward with the mastoid antrum.

Adventitious: Occurring sometime after birth.

Afferent: Nerves that carry impulses from the periphery toward the brain.

Affricate: A combination of a stop and fricative phoneme.

Age-equivalent score: The average score for people of a given age.

Agnosia: Sensory deficit accompanying some aphasias that make it difficult to understand incoming sensory information.

Agrammatism: Omission of spoken and written grammatical elements found in some aphasias in which individuals omit short unstressed words and morphological endings.

Agraphia: Writing difficulty accompanying some aphasias and characterized by mistakes and poorly formed letters.

AIDS: See Human immunodeficiency virus.

Air conduction: The course of sounds that are conducted to the inner ear by way of the outer ear and middle ear.

Air-bone gap (ABG): The amount by which the air-conduction threshold of a patient exceeds the bone-conduction threshold at any frequency in the same ear.

Alexia: Reading difficulties found in some aphasias in which the client may be unable to recognize even common words that he or she says.

Allele: One of two or more forms of a gene occupying corresponding locations on corresponding chromosomes.

Allophone: A phonemic variation.

ALS: See Amyotrophic lateral sclerosis.

Alternate binaural loudness balance (ABLB): test A procedure that tests for recruitment in unilateral hearing losses. The growth of loudness of pure tones in the impaired ear is compared with that of the opposite (normal) ear as a function of increasing intensity.

Alveolus: Area of the mandible and maxilla which houses the teeth.

Alzheimer's disease: A cortical pathology that affects primarily memory, language, or visuospatial skills as a result of diffuse brain atrophy; presenile dementia.

American Sign Language (ASL): A complex, nonvocal language containing elaborate syntax and semantics. The primary method by which a deaf individual becomes part of the American Deaf culture.

Amplification: Personal hearing aids, cochlear implants, and FM assistive listening devices; often a first step in aural rehabilitation.

Amplitude distortion: The presence of frequencies in the output of an electroacoustic system that were not present at the input, resulting in a disproportional difference between the input and output waves.

Amplitude: The extent of the vibratory movement of a mass from its position of rest to that point furthest from the position of rest.

Ampulla: The widened end of each of the three semicircular canals where they return to the utricle. Each ampulla contains an end organ for the sense of equilibrium.

Amyotrophic lateral sclerosis (ALS): Commonly called Lou Gehrig's disease, ALS is a rapidly progressive degenerative disease in which the individual gradually loses control of her or his musculature. It is characterized by fatigue, muscle atrophy or loss of bulk, involuntary contractions, and reduced muscle tone. Speech in the later stages is labored and slow with short phrasing, long pauses, hypernasality, and severely impaired articulation.

Analog hearing aid: An amplification system in which the electrical signal is analogous to the input acoustical signal in frequency, intensity, and temporal patterns.

Anatomy: The study of the structures of the body and the relationship of these structures to one another.

Anechoic chamber: A specially built room with large wedges of sound-absorbing material on all walls, floor, and ceiling. The purpose of the room is to provide maximum sound absorption and to keep reverberation to an absolute minimum.

Aneurysm : A type of hemorrhagic stroke resulting from the rupture of a sac-like bulging in a weakened artery wall.

Angular gyrus: The area of the brain that assists in integrating visual, auditory, and tactile information and linguistic representation.

Ankyloglossia: Tongue-tie; a relatively short lingual frenum.

Annulus: The ring of tissue around the periphery of the tympanic membrane that holds it in position at the end of the external auditory canal.

Anomia: Difficulty naming entities.

Anomic aphasia: A fluent aphasia characterized by naming difficulties and mild to moderate auditory comprehension problems.

Anotia: Absence of the pinna.

Anoxia: Deprivation of oxygen to specific cells of the body affecting their normal metabolism.

Aperiodic wave: A waveform that does not repeat over time.

Apgar Test: A method for evaluating the status of infants immediately and shortly after birth. Observations are made of the child's respiration, heart rate, muscle tone, color, and reflex irritability.

Aphasia: An impairment due to localized brain injury and affecting understanding, retrieving, and formulating meaningful and sequential elements of language.

Aphonia : Persistent absence of voice that is perceived as whispering.

Aplasia: Hearing loss due to the absence or malformation of the inner ear structures during embryonic development.

Apraxia of speech or verbal apraxia: A neurological impairment of the ability to program-organize and plan-and execute movement of the speech muscles, unrelated to muscle weakness, slowness, or paralysis.

Arbitrary symbols: Based on judgment or decision rather than "natural" law (e.g., letters and words).

Arcuate fasciculus: A white fibrous tract below the cortex that connects Wernicke's and Broca's areas.

Arteriovenous malformation: A rare type of ischemic stroke resulting from a poorly formed tangle of arteries and veins in which arterial walls are weak and give way under pressure.

Articulation : Rapid and coordinated movement of the tongue, teeth, lips, and palate to produce speech sounds.

Articulatory/resonating system: Structures used during sound production including the oral cavity, nasal cavity, tongue, and soft palate.

Artifacts: Objects such as clothing that communicate information about people.

Artificial ear: A device for calibrating air-conduction earphones. It consists of a 6 cm3 coupler to connect an earphone to a condenser microphone with cathode follower and a meter that reads in dB SPL. When calibrating insert earphones, a 2 cm3 coupler must be used.

Artificial mastoid: A device for calibrating bone-

Aryepiglottic folds: The membrane and muscle that connect the sides of the epiglottis to the arytenoid cartilages in the larynx.

Arytenoid cartilages: Small cartilages on the posterior aspect of the cricoid cartilage that serve as the posterior attachments of the vocal folds.

ASHA: The American Speech-Language-Hearing Association.

Aspiration: Inhaling; used to mean the inhalation of fluid or food into the lungs; in phonology, a puff of air that is released in the production of various allophones.

Assessment of communicative disorders: The systematic process of obtaining information from many sources, through various means, and in different settings to verify and specify communication strengths and weaknesses, identify possible causes, and make plans to address them.

Assistive listening device (ALDS): Any of several types of equipment, other than a conventional hearing aid, that amplifies or enhances hearing, for example, FM systems and telephone and television amplifiers.

Ataxia: Disorder of muscle coordination.

Ataxic cerebral palsy: A congenital disorder characterized by uncoordinated movement and disturbed balance. Movements lack direction, and hypotonic muscles lack adequate force and rate and have poor directional control.

Ataxic dysarthria: A motor speech disorder involving a combination of muscle weakness or reduced tone or hypotonia and problems with muscle coordination. Little or no paralysis exists, and the problem is one involving the accuracy, timing, and direction of movement. Speech is characterized by excessive and equal stress and imprecise articulation especially in repetitive movements.

Athetoid cerebral palsy: A congenital disorder characterized by athetosis, a slow involuntary writhing that is most pronounced when the individual attempts volitional movement. The resultant behavior may be disorganized and uncoordinated.

Athetosis: One of the three major categories of cerebral palsy, characterized by squirming or writhing movements.

Atresia: Congenital closure of a normally open body orofice, such as the ear canal, either at the pinna or within the ear canal, that may result in a conductive hearing loss.

Atropine: A medication that is used to control drooling.

Attention deficit hyperactivity disorder (ADHD): Hyperactivity and attentional difficulties in children who do not manifest other characteristics of learning disabilities.

Attenuation: The reduction of energy (e.g., sound).

Audible prolongation: Stuttering behavior in which production of a sound is excessively sustained, as in "sssssss-snow."

Audiogram: A graphic representation of audiometric findings showing hearing levels as a function of frequency.

Audiological rehabilitation: Treatment of those with adventitious hearing loss to improve communication through hearing aids, hearing therapy, speechreading, and counseling. Audiological habilitation of children may also include speech and language therapy, auditory training, and manual communication. Also known as aural rehabilitation.

Audiologist: A professional whose distinguishing role is to identify, assess, manage, and prevent disorders of hearing and balance.

Audiology: "The discipline involved in the prevention, identification, and evaluation of hearing disorders, the selection and evaluation of hearing aids, and the habilitation/rehabilitation of individuals with hearing impairment" (Bess & Humes, 1995, p. 6).

Audiometer (pure-tone): A device for determining the thresholds of hearing. Pure tones at various frequencies are generated, and their levels are increased and decreased until thresholds are found. Outputs may include earphones for air-conduction testing, a bone conduction vibrator for bone-conduction testing, and one or more loudspeakers for sound field testing.

Audiometric Weber test: An extension of the tuning-fork Weber test. The bone-conduction vibrator of the audiometer is applied to the forehead of a patient, and tones are presented above threshold. The patient is directed to respond by stating whether the tone was heard in the right ear, the left ear, or the midline.

Auditory bombardment: In phonological therapy, the repeated presentation of target phonemes at a slightly amplified level.

Auditory brain stem evoked response (ABER) audiometry: A type of electrophysiological testing in which electrodes placed at various points on the scalp gather and record neural responses generated as a "sound" progresses from the auditory nerve to designated points along the brain stem. The result is a waveform known as a Jewett wave.

Auditory brainstem response (ABR): The seven wavelets that appear within 10 milliseconds after signal presentation.

Auditory event-related potentials (ERPs): AEPs that occur after latencies of about 60 milliseconds, with the largest positive wave at about 300 milliseconds. Patients must cooperate by counting "oddball" stimuli.

Auditory evoked potentials (AEPs): The use of summing or averaging computers to observe the very small electrical responses to sound from the cochlea, brainstem, and cortex.

Auditory middle latency response (AMLR): Responses that occur 10 to 50 milliseconds after signal onset and are thought to arise from the upper brainstem.

Auditory nerve: The VIIIth cranial nerve that connects the inner ear to the brain stem.

Auditory nervous system: The brain stem pathways and the auditory cortex of the brain.

Auditory neuropathy: A mild to moderate sensorineural hearing loss with speech recognition difficulties disproportionate to degree of loss. In contrast to acoustic neuroma, there is an unexpected absence of ABR wave forms and a normal MRI.

Auditory placode: A thickened plate, near the hindbrain in the human embryo, that develops into the inner ear.

Auditory radiations: A bundle of nerve fibers passing from the medial geniculate body to the temporal gyri of the cerebral cortex.

Auditory training: Teaching a person with a hearing impairment how to use the residual or remaining hearing that is available to him or her with the goal of maximizing use of speech and nonspeech cues. The term also applies to intervention with people with phonological and articulatory disorders in which the client is trained to listen to particular sounds.

Auditory tube: See Eustachian tube.

Auditory Reference: to the sense of hearing.

Aural rehabilitation: Treatment to improve communication ability of those with hearing loss acquired after the development of spoken language.

Aural/oral communication method: An approach to teaching communication skills to individuals with hearing impairment that emphasizes the use of residual hearing to receive language and the spoken word to express language and places heavy emphasis on use of amplification, auditory training, and speech-language therapy.

Auricle: The cartilaginous appendage of the external ear.

Auropalpebral reflex (APR): Contraction of the ring muscles of the eyes in response to a sudden, unexpected sound.

Authentic data: Information about an individual that is based on real life.

Autism: A severe form of pervasive developmental disorder characterized as an impairment in reciprocal social interaction with a severely limited behavior, interest, and activity repertoire that has its onset before thirty months of age (American Psychiatric Association, 1987).

Automatic gain control: A special circuit within a hearing aid that prevents sounds from being overamplified for the impaired ear.

Automaticity: The ease with which a person uses a particular skill without apparent thought.

Autophony: A condition produced by some middle-ear or eustachian tube abnormalities, in which individuals' voices seem louder than normal to themselves.

Autosomal dominant: The capacity of a gene to express itself when carried by only one of a pair of homologous chromosomes.

Autosomal recessive: The inability of a gene to express a trait unless it is carried by both members of a pair of homologous chromosomes.

Autosome: Any chromosome other than a sex chromosome. There are 22 pairs in humans.

Axon: The efferent portion of a neuron.