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Hearing (sense)
Hearing, or auditory perception, is the ability to perceive sounds through an organ, such as an ear, by detecting vibrations as periodic changes in the pressure of a surrounding medium. The academic field concerned with hearing is auditory science. Sound may be heard through solid, liquid, or gaseous matter. It is one of the traditional five senses. Partial or total inability to hear is called hearing loss. In humans and other vertebrates, hearing is performed primarily by the auditory system: mechanical waves, known as vibrations, are detected by the ear and transduced into nerve impulses that are perceived by the brain (primarily in the temporal lobe). Like touch, audition requires sensitivity to the movement of molecules in the world outside the organism. Both hearing and touch are types of mechanosensation. Hearing mechanism There are three main components of the human auditory system: the outer ear, the middle ear, and the inner ear. Outer ear The ou ...
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Psychoacoustics
Psychoacoustics is the branch of psychophysics involving the scientific study of sound perception and audiology—how humans perceive various sounds. More specifically, it is the branch of science studying the psychological responses associated with sound (including noise, speech, and music). Psychoacoustics is an interdisciplinary field of many areas, including psychology, acoustics, electronic engineering, physics, biology, physiology, and computer science. Background Hearing is not a purely mechanical phenomenon of wave propagation, but is also a sensory and perceptual event; in other words, when a person hears something, that something arrives at the ear as a mechanical sound wave traveling through the air, but within the ear it is transformed into neural action potentials. The outer hair cells (OHC) of a mammalian cochlea give rise to enhanced sensitivity and better frequency resolution of the mechanical response of the cochlear partition. These nerve pulses then travel to ...
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Impedance Matching
In electronics, impedance matching is the practice of designing or adjusting the input impedance or output impedance of an electrical device for a desired value. Often, the desired value is selected to maximize power transfer or minimize signal reflection. For example, impedance matching typically is used to improve power transfer from a radio transmitter via the interconnecting transmission line to the antenna. Signals on a transmission line will be transmitted without reflections if the transmission line is terminated with a matching impedance. Techniques of impedance matching include transformers, adjustable networks of lumped resistance, capacitance and inductance, or properly proportioned transmission lines. Practical impedance-matching devices will generally provide best results over a specified frequency band. The concept of impedance matching is widespread in electrical engineering, but is relevant in other applications in which a form of energy, not necessari ...
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Acoustic Impedance
Acoustic impedance and specific acoustic impedance are measures of the opposition that a system presents to the acoustic flow resulting from an acoustic pressure applied to the system. The SI unit of acoustic impedance is the pascal-second per cubic metre (), or in the MKS system the rayl per square metre (), while that of specific acoustic impedance is the pascal-second per metre (), or in the MKS system the rayl. There is a close analogy with electrical impedance, which measures the opposition that a system presents to the electric current resulting from a voltage applied to the system. Mathematical definitions Acoustic impedance For a linear time-invariant system, the relationship between the acoustic pressure applied to the system and the resulting acoustic volume flow rate through a surface perpendicular to the direction of that pressure at its point of application is given by: : p(t) = * Qt), or equivalently by : Q(t) = * pt), where * ''p'' is the acoustic pressure; * ...
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Cochlea
The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus. A core component of the cochlea is the Organ of Corti, the sensory organ of hearing, which is distributed along the partition separating the fluid chambers in the coiled tapered tube of the cochlea. The name cochlea derives . Structure The cochlea (plural is cochleae) is a spiraled, hollow, conical chamber of bone, in which waves propagate from the base (near the middle ear and the oval window) to the apex (the top or center of the spiral). The spiral canal of the cochlea is a section of the bony labyrinth of the inner ear that is approximately 30 mm long and makes 2 turns about the modiolus. The cochlear structures include: * Three ''scalae'' or chambers: ** the vestibular duct or ''scala vestibuli'' (containing perilymph), which lies superior to the cochlear duct and abuts the oval window ** th ...
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Ossicles
The ossicles (also called auditory ossicles) are three bones in either middle ear that are among the smallest bones in the human body. They serve to transmit sounds from the air to the fluid-filled labyrinth (cochlea). The absence of the auditory ossicles would constitute a moderate-to-severe hearing loss. The term "ossicle" literally means "tiny bone". Though the term may refer to any small bone throughout the body, it typically refers to the malleus, incus, and stapes (hammer, anvil, and stirrup) of the middle ear. Structure The ossicles are, in order from the eardrum to the inner ear (from superficial to deep): the malleus, incus, and stapes, terms that in Latin are translated as "the hammer, anvil, and stirrup". * The malleus ( la, "hammer") articulates with the incus through the incudomalleolar joint and is attached to the tympanic membrane ( eardrum), from which vibrational sound pressure motion is passed. * The incus ( la, "anvil") is connected to both the ...
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Sebaceous Gland
A sebaceous gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in the greatest number on the face and scalp, but also on all parts of the skin except the palms of the hands and soles of the feet. In the eyelids, meibomian glands, also called tarsal glands, are a type of sebaceous gland that secrete a special type of sebum into tears. Surrounding the female nipple, areolar glands are specialized sebaceous glands for lubricating the nipple. Fordyce spots are benign, visible, sebaceous glands found usually on the lips, gums and inner cheeks, and genitals. Structure Location Sebaceous glands are found throughout all areas of the skin, except the palms of the hands and soles of the feet. There are two types of sebaceous glands, those connected to hair follicles and those that exist independently. Sebaceous ...
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Ceruminous Gland
Ceruminous glands are specialized sudoriferous glands (sweat glands) located subcutaneously in the external auditory canal, in the outer 1/3. Ceruminous glands are simple, coiled, tubular glands made up of an inner secretory layer of cells and an outer myoepithelial layer of cells. They are classed as apocrine glands. The glands drain into larger ducts, which then drain into the guard hairs that reside in the external auditory canal. Here they produce cerumen, or earwax, by mixing their secretion with sebum and dead epidermal cells. Cerumen keeps the eardrum pliable, lubricates and cleans the external auditory canal, waterproofs the canal, kills bacteria, and serves as a barrier to trap foreign particles (dust, fungal spores, etc.) by coating the guard hairs of the ear, making them sticky. These glands are capable of developing both benign and malignant tumors. The benign Malignancy () is the tendency of a medical condition to become progressively worse. Malignancy is mo ...
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Cerumen
Earwax, also known by the medical term cerumen, is a brown, orange, red, yellowish or gray waxy substance secreted in the ear canal of humans and other mammals. It protects the skin of the human ear canal, assists in cleaning and lubrication, and provides protection against bacteria, fungi, and water. Earwax consists of dead skin cells, hair, and the secretions of cerumen by the ceruminous and sebaceous glands of the outer ear canal. Major components of earwax are long chain fatty acids, both saturated and unsaturated, alcohols, squalene, and cholesterol. Excess or compacted cerumen is the buildup of ear wax causing a blockage in the ear canal and it can press against the eardrum or block the outside ear canal or hearing aids, potentially causing hearing loss. Physiology Cerumen is produced in the cartilaginous portion which is the outer third portion of the ear canal. It is a mixture of viscous secretions from sebaceous glands and less-viscous ones from modified ap ...
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Waveform
In electronics, acoustics, and related fields, the waveform of a signal is the shape of its graph as a function of time, independent of its time and magnitude scales and of any displacement in time.David Crecraft, David Gorham, ''Electronics'', 2nd ed., , CRC Press, 2002, p. 62 In electronics, the term is usually applied to periodically varying voltages, currents, or electromagnetic fields. In acoustics, it is usually applied to steady periodic sounds—variations of pressure in air or other media. In these cases, the waveform is an attribute that is independent of the frequency, amplitude, or phase shift of the signal. The term can also be used for non-periodic signals, like chirps and pulses. The waveform of an electrical signal can be visualized in an oscilloscope or any other device that can capture and plot its value at various times, with a suitable scales in the time and value axes. The electrocardiograph is a medical device to record the waveform of t ...
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Vertical Sound Localization
Sound localization is a listener's ability to identify the location or origin of a detected sound in direction and distance. The sound localization mechanisms of the mammalian auditory system have been extensively studied. The auditory system uses several cues for sound source localization, including time difference and level difference (or intensity difference) between the ears, and spectral information. These cues are also used by other animals, such as birds and reptiles, but there may be differences in usage, and there are also localization cues which are absent in the human auditory system, such as the effects of ear movements. Animals with the ability to localize sound have a clear evolutionary advantage. How sound reaches the brain Sound is the perceptual result of mechanical vibrations traveling through a medium such as air or water. Through the mechanisms of compression and rarefaction, sound waves travel through the air, bounce off the pinna and concha of the exter ...
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Filter (signal Processing)
In signal processing, a filter is a device or process that removes some unwanted components or features from a signal. Filtering is a class of signal processing, the defining feature of filters being the complete or partial suppression of some aspect of the signal. Most often, this means removing some frequencies or frequency bands. However, filters do not exclusively act in the frequency domain; especially in the field of image processing many other targets for filtering exist. Correlations can be removed for certain frequency components and not for others without having to act in the frequency domain. Filters are widely used in electronics and telecommunication, in radio, television, audio recording, radar, control systems, music synthesis, image processing, and computer graphics. There are many different bases of classifying filters and these overlap in many different ways; there is no simple hierarchical classification. Filters may be: * non-linear or linear * time-vari ...
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