Auditory Threshold: The audibility limit of discriminating sound intensity and pitch.Audiometry: The testing of the acuity of the sense of hearing to determine the thresholds of the lowest intensity levels at which an individual can hear a set of tones. The frequencies between 125 and 8000 Hz are used to test air conduction thresholds and the frequencies between 250 and 4000 Hz are used to test bone conduction thresholds.Audiometry, Pure-Tone: Measurement of hearing based on the use of pure tones of various frequencies and intensities as auditory stimuli.Cochlear Diseases: Pathological processes of the snail-like structure (COCHLEA) of the inner ear (LABYRINTH) which can involve its nervous tissue, blood vessels, or fluid (ENDOLYMPH).Hearing Loss, Noise-Induced: Hearing loss due to exposure to explosive loud noise or chronic exposure to sound level greater than 85 dB. The hearing loss is often in the frequency range 4000-6000 hertz.Hearing: The ability or act of sensing and transducing ACOUSTIC STIMULATION to the CENTRAL NERVOUS SYSTEM. It is also called audition.Evoked Potentials, Auditory, Brain Stem: Electrical waves in the CEREBRAL CORTEX generated by BRAIN STEM structures in response to auditory click stimuli. These are found to be abnormal in many patients with CEREBELLOPONTINE ANGLE lesions, MULTIPLE SCLEROSIS, or other DEMYELINATING DISEASES.Melopsittacus: A genus, commonly called budgerigars, in the family PSITTACIDAE. In the United States they are considered one of the five species of PARAKEETS.Cochlea: The part of the inner ear (LABYRINTH) that is concerned with hearing. It forms the anterior part of the labyrinth, as a snail-like structure that is situated almost horizontally anterior to the VESTIBULAR LABYRINTH.Noise: Any sound which is unwanted or interferes with HEARING other sounds.Hearing Loss: A general term for the complete or partial loss of the ability to hear from one or both ears.Acoustic Stimulation: Use of sound to elicit a response in the nervous system.Sensory Thresholds: The minimum amount of stimulus energy necessary to elicit a sensory response.Differential Threshold: The smallest difference which can be discriminated between two stimuli or one which is barely above the threshold.Pain Threshold: Amount of stimulation required before the sensation of pain is experienced.Ketamine: A cyclohexanone derivative used for induction of anesthesia. Its mechanism of action is not well understood, but ketamine can block NMDA receptors (RECEPTORS, N-METHYL-D-ASPARTATE) and may interact with sigma receptors.Anesthetics, Dissociative: Intravenous anesthetics that induce a state of sedation, immobility, amnesia, and marked analgesia. Subjects may experience a strong feeling of dissociation from the environment. The condition produced is similar to NEUROLEPTANALGESIA, but is brought about by the administration of a single drug. (From Gilman et al., Goodman and Gilman's The Pharmacological Basis of Therapeutics, 8th ed)Isoflurane: A stable, non-explosive inhalation anesthetic, relatively free from significant side effects.Periodicals as Topic: A publication issued at stated, more or less regular, intervals.Audiometry, Evoked Response: A form of electrophysiologic audiometry in which an analog computer is included in the circuit to average out ongoing or spontaneous brain wave activity. A characteristic pattern of response to a sound stimulus may then become evident. Evoked response audiometry is known also as electric response audiometry.Chinchilla: A genus of the family Chinchillidae which consists of three species: C. brevicaudata, C. lanigera, and C. villidera. They are used extensively in biomedical research.Noise, Occupational: Noise present in occupational, industrial, and factory situations.Ear Protective Devices: Personal devices for protection of the ears from loud or high intensity noise, water, or cold. These include earmuffs and earplugs.Stainless Steel: Stainless steel. A steel containing Ni, Cr, or both. It does not tarnish on exposure and is used in corrosive environments. (Grant & Hack's Chemical Dictionary, 5th ed)Dictionaries, MedicalDark Adaptation: Adjustment of the eyes under conditions of low light. The sensitivity of the eye to light is increased during dark adaptation.Dictionaries as Topic: Lists of words, usually in alphabetical order, giving information about form, pronunciation, etymology, grammar, and meaning.Photoreceptor Cells: Specialized cells that detect and transduce light. They are classified into two types based on their light reception structure, the ciliary photoreceptors and the rhabdomeric photoreceptors with MICROVILLI. Ciliary photoreceptor cells use OPSINS that activate a PHOSPHODIESTERASE phosphodiesterase cascade. Rhabdomeric photoreceptor cells use opsins that activate a PHOSPHOLIPASE C cascade.Auditory Cortex: The region of the cerebral cortex that receives the auditory radiation from the MEDIAL GENICULATE BODY.Auditory Fatigue: Loss of sensitivity to sounds as a result of auditory stimulation, manifesting as a temporary shift in auditory threshold. The temporary threshold shift, TTS, is expressed in decibels.Neurons: The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the NERVOUS SYSTEM.Postural Balance: A POSTURE in which an ideal body mass distribution is achieved. Postural balance provides the body carriage stability and conditions for normal functions in stationary position or in movement, such as sitting, standing, or walking.HungaryArousal: Cortical vigilance or readiness of tone, presumed to be in response to sensory stimulation via the reticular activating system.Accidental Falls: Falls due to slipping or tripping which may result in injury.Sensation Disorders: Disorders of the special senses (i.e., VISION; HEARING; TASTE; and SMELL) or somatosensory system (i.e., afferent components of the PERIPHERAL NERVOUS SYSTEM).Posture: The position or attitude of the body.Gait: Manner or style of walking.Hearing Aids: Wearable sound-amplifying devices that are intended to compensate for impaired hearing. These generic devices include air-conduction hearing aids and bone-conduction hearing aids. (UMDNS, 1999)Hearing Tests: Part of an ear examination that measures the ability of sound to reach the brain.Hearing Disorders: Conditions that impair the transmission of auditory impulses and information from the level of the ear to the temporal cortices, including the sensorineural pathways.Hearing Loss, Sensorineural: Hearing loss resulting from damage to the COCHLEA and the sensorineural elements which lie internally beyond the oval and round windows. These elements include the AUDITORY NERVE and its connections in the BRAINSTEM.Hearing Loss, High-Frequency: Hearing loss in frequencies above 1000 hertz.Birth Certificates: Official certifications by a physician recording the individual's birth date, place of birth, parentage and other required identifying data which are filed with the local registrar of vital statistics.Airports: Terminal facilities used for aircraft takeoff and landing and including facilities for handling passengers. (from McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed.)Pediatrics: A medical specialty concerned with maintaining health and providing medical care to children from birth to adolescence.Whales, Pilot: The genus Globicephala, in the family Delphinidae, consisting of two species of DOLPHINS. They are mostly black with a stocky shape and bulbous foreheads.Whales: Large marine mammals of the order CETACEA. In the past, they were commercially valued for whale oil, for their flesh as human food and in ANIMAL FEED and FERTILIZERS, and for baleen. Today, there is a moratorium on most commercial whaling, as all species are either listed as endangered or threatened.Fin Whale: The species Balaenoptera physalus, in the family Balaenopteridae, characterized by a large, strongly curved, dorsal fin. It is the second largest of the WHALES, highly migratory, but rarely seen near the shore.Beluga Whale: The species Delphinapterus leucas, in the family Monodontidae, found primarily in the Arctic Ocean and adjoining seas. They are small WHALES lacking a dorsal fin.Morbillivirus: A genus of the family PARAMYXOVIRIDAE (subfamily PARAMYXOVIRINAE) where the virions of most members have hemagglutinin but not neuraminidase activity. All members produce both cytoplasmic and intranuclear inclusion bodies. MEASLES VIRUS is the type species.Morbillivirus Infections: Infections with viruses of the genus MORBILLIVIRUS, family PARAMYXOVIRIDAE. Infections mainly cause acute disease in their hosts, although in some cases infection is persistent and leads to degenerative conditions.Cetacea: An order of wholly aquatic MAMMALS occurring in all the OCEANS and adjoining seas of the world, as well as in certain river systems. They feed generally on FISHES, cephalopods, and crustaceans. Most are gregarious and most have a relatively long period of parental care and maturation. Included are DOLPHINS; PORPOISES; and WHALES. (From Walker's Mammals of the World, 5th ed, pp969-70)