NationMaster - Encyclopedia: Audiograms in mammals

An audiogram is used to show the quietest sounds someone can hear at different frequencies Hz (pitches). The quietest sound someone can hear is known as their hearing threshold. The intensity of the sounds is measured in decibels (dB), 0 dB is the average human threshold of hearing at 1000Hz. So the scale ranges from -10 dB to 100 dB. The frequencies are along the x axis of the audiogram, in human audiograms these range from 250Hz to 8000Hz. This is not the full range of frequencies that humans can hear but they are the frequencies that are most important when looking into hearing loss. So when reading an audiogram, we can see that for a specific frequency, what intensity the sound needs to be presented for the person to be able to hear it. An audiogram is a graphical representation of how well a certain person can perceive different sound frequencies. ... Threshold of hearing is the sound pressure level SPL of 20 µPa (micropascal) = 2 × 10-5 Pascal (Pa). ... The decibel is a dimensionless unit (like percent) that is a measure of ratios on a logarithmic scale. ... FreQuency is a music video game developed by Harmonix and published by SCEI. It was released in November 2001. ... In physics, intensity is a measure of the time-averaged energy flux. ...

Hearing thresholds of humans and other mammals can be found by using behavioural hearing tests or physiological tests. An audiogram can be obtained using a behavioural hearing test called Audiometry. For humans the test involves different tones being presented at a specific frequency (pitch) and intensity (loudness). When the person hears the sound they raise their hand or press a button so that the tester knows that they have heard it. The lowest intensity sound they can hear is recorded. The test varies for children, their response to the sound can be a head turn or using a toy. The child learns what they can do when they hear the sound, for example they are taught that when they heard the sound they can put they toy man in the boat. A similar technique can be used when testing some animals. But instead of a toy food can be used as a reward for responding to the sound. Physiological tests do not need the patient to respond. For example when performing the auditory evoked potentials the patient’s brainstem responses are being measured when a sound is played into their ear. Orders Subclass Monotremata Monotremata Subclass Marsupialia Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Subclass Placentalia Xenarthra Dermoptera Desmostylia Scandentia Primates Rodentia Lagomorpha Insectivora Chiroptera Pholidota Carnivora Perissodactyla Artiodactyla Cetacea Afrosoricida Macroscelidea Tubulidentata Hyracoidea Proboscidea Sirenia The mammals are the class of vertebrate animals primarily characterized by the presence of mammary... Pitch may refer to: Look up Pitch in Wiktionary, the free dictionary. ... Loudness is the quality of a sound which is high in volume (amplitude, or sound pressure). ...

The information on different mammals hearing was obtained primarily by behavioural hearing tests.

Human hearing

Frequency ranges in mammals

Land mammals

Dogs

The hearing ability of a dog is dependant on its breed and age. However, the range of hearing is approximately 40 to 60, 000 Hz, which is much greater than that of humans. As with humans, some dog breeds become deaf with age, such as the German Shepard and Miniature Poodle. When dogs hear a sound, they will move their ears towards it, in order to gain maximised reception. In order to achieve this, the ears of a dog are controlled by at least 18 muscles. This allows the ears to tilt and rotate. Ear shape also allows for the sound to be more accurately heard. Many breeds often have upright and curved ears, which direct and amplify the sounds. As dogs hear much higher frequency sounds to humans, they have a different perception of the world in comparison to humans. Sounds that seem loud to humans often emit high frequency tones that can scare away dogs and ultrasonic signals are used in training whistles as a dog will respond much better to such levels. In the wild dogs use their hearing capabilities to hunt and locate food and domestic breeds are often used as guard dogs due to their increased hearing ability. Trinomial name Canis lupus familiaris The dog Canis lupus is a type of canine, a mammal in the order Carnivora. ... The German Shepherd Dog or Alsatian (See History), is a breed of dog. ...

Bats

Mice

Mice have large ears in comparison to their bodies; if we compare the relative size of our ears and mice ears we can see a large difference. Mice hear higher frequencies then humans; their frequency range is 10kHz to 70kHz. They do not hear the lower frequencies that we can; therefore they communicate using high frequency noises that are inaudible for humans. The distress call of a young mouse can be produced at 40kHz. The mice use their ability to produce and hear sounds out of our and other predators frequency ranges to their advantage. They can alert other mice of danger without also alerting the predator to their presence. The squeaks that we can hear a mouse make are lower in frequency and are used by the mouse to make longer distance calls, as the low frequency sound can travel further then the high frequency sounds. Mice may refer to: An abbreviation of Meetings, Incentives, Conferencing, Exhibitions. ... The frequency range is defined as the range of frequencies in which the device is allowed to operate. ... Communication is the process of exchanging information usually via a common system of symbols. ... Feral mouse A mouse (plural mice) is a rodent that belongs to one of numerous species of small mammals. ... This snapping turtle is trying to make a meal of a Canada goose, but the goose is too wary. ... FreQuency is a music video game developed by Harmonix and published by SCEI. It was released in November 2001. ...

Marine Mammals

Marine mammals are mammals that primarily inhabit marine environments. There are many different types and all vary in terms of form and function. As the environment in which they live completely contrasts the habitat of land mammals, there are many differences in evolution. Due to this, the internal functioning of marine mammals varies to that of the land mammals. These differences extend as far as the auditory system, leading to an extensive amount of research being carried out for this select group of mammals. A marine mammal is a mammal that is primarily ocean-dwelling or depends on the ocean for its food. ...

We realise through advanced technology that humans rely on the ocean and its delicate balance of life forms that reside within the great vast depths under the surface. These marine species form a delicate chain that has gone untouched and unchanged for millennia, but modern technology is changing that maybe forever. The world’s oceans are a very noisy environment due to naturally occurring sounds like volcanic eruptions and fault-line shifts, these naturally occurring acoustical signals have been happening for millennia and as such the marine species have adapted to them. However modern times has increased the sounds in the world’s oceans exponentially, as a consequence marine species are finding it increasingly difficult to navigate and communicate with each other while in the presence of this interference. Scientists are at present collecting data pertaining to marine species range of hearing, to hopefully better understand the problems caused by man-made marine equipment in the underwater environment. Some studies have shown a worrying link between the man-made sounds and possible trauma being caused to the marine species while in the sound field of these highly powerful emitters. These emitters are usually found aboard military and large commercial vessels like the ones used for scanning the worlds oceans looking for ship wrecks and military hardware lost to the depths of the ocean, they all employ some form of highly focused sonar device capable of scanning several miles of ocean at once. The problems seem to arise from a large collection of vessels using sonar actively to scan a particular area, while on their own they only cause minor irritation to the marine species but collectively the problem is exacerbated. Marine species have been found to beach themselves in great numbers when in the presence of these active sonar scans. Npower commissioned a report to highlight this problem. This has been reported on several occasions in varying geographical locations over several years. Only recently have we been aware of these underlying problems with increased noise and its devastating consequences on the world’s marine creatures. Further study is on-going to try and unravel the mysteries of the relationship between marine species, man-made sonar and noise pollution. The goal: to try and use the equipment we have made to better serve the underwater world we share and live in. This and other fields related to this study are at the forefront of current marine scientists remits worldwide. NPower is a national network of nonprofit technology assistance providers based in Seattle, WA, USA. // Mission ...to ensure all nonprofits can use technology to better serve their communities. ...

Bottlenose Dolphins

One of the more commonly tested marine mammals is the bottlenose dolphin, mainly due to them being found in captivity, making testing much easier. Much testing has been carried out to determine the pathway of auditory signals as it is believed that marine mammals possess a different auditory system to that of land mammals. Binomial name Tursiops truncatus Montagu, 1821 Bottlenose Dolphin range (in blue) The Bottlenose Dolphin (Tursiops truncatus) is the most common and well-known dolphin species. ...

The auditory system of a land mammal typically works via the transfer of sound waves through the ear canals. If such mammals are submerged underwater, the traditional methods of auditory transmission cannot be sustained. Instead the sound is transmitted via bone conduction at all angles around the skull. Due to this process however there is a loss of localisation ability, partially due to an impedance mismatch between the water and cranial tissue.

In the dolphin population and in other toothed whales however, this process does not occur. The auditory organs are isolated from the skull, preventing mass bone conduction from taking place.

It has been found through numerous experiments, that dolphins and similar species of marine mammal have two potential ways of hearing; one for low frequency signals and one for echolocation signals. The first is similar to that of land mammals. Bottlenose dolphins have an external meatus, as found in humans, and despite often being filled with cellular debris, particularly in adult dolphins, tests have shown that it acts as an auditory pathway. Electrophysiological tests have found minimum audible threshold levels, when sounds are played below 20-30 Hz, just above the external meatus. Image File history File links Previously Dolphin. ... Image File history File links Previously Dolphin. ...

Dolphins use the process of echolocation to determine the position of objects, such as prey. Studies have shown that echolocation signals are transmitted through a process similar to bone conduction. It is thought that the sounds travel from the water to the dolphin, via the mandibular fat channels, found in the lower jaw. As this area has a similar impendance to that of the water, transmission is much faster. See: Animal echolocation: animals emitting sound waves and listening to the echo in order to locate objects or navigate. ...

Studies have found there to be two different types of cochlea in the dolphin population. Type one has been found in the Amazon River dolphin and harbour porpoises. These types of dolphin communicate with high frequency signals that are better suited to travelling shorter distances. It has been found that the harbour porpoise emits click sounds in two frequency bands, one at 2 kHz and one between 120-140 kHz. The cochlear in these dolphins is specialised to accommodate high frequency sounds and its basilar membrane is narrower at the apex. Cross section of the cochlea. ...

The second type of cochlear is found in offshore and open water species of dolphin, such as the bottlenose dolphin. The sounds produced by Bottlenose dolphins are low frequency and range between 0.25 to 150 kHz. The higher frequencies in this range make up echolocation and the majority of the low frequencies are for social interaction as the signals travel much further distances.

These frequency ranges relates to the thresholds obtained from studies of dolphins. Look up Threshold in Wiktionary, the free dictionary A threshold is a fixed location or value where an abrupt change is observed. ...

Marine mammals use vocalisations in many different ways. Dolphins communicate via clicks and whistles, and whales use low frequency moans or pulse signals. Each signal varies in terms of frequency and different signals are used to communicate different aspects. In dolphins echolocation is used in order to detect and characterise objects and clicks and whistles are used in sociable herds as identification and communication devices. The auditory system of marine mammals is adapted to enable these forms of communication. This is shown through the evolution of the positioning of the auditory processes in dolphins, and the specialised cochlea’s found in dolphins dependant on their habitat.

References

Contents

Introduction to hearing audiograms

Audiograms

Human hearing

Frequency ranges in mammals

Land mammals

Dogs

Bats

Mice

Marine Mammals

Bottlenose Dolphins

References

See also

Contents

Introduction to hearing audiograms GA_googleFillSlot("encyclopedia_square");

Audiograms

Human hearing

Frequency ranges in mammals

Land mammals

Dogs

Bats

Mice

Marine Mammals

Bottlenose Dolphins

References

See also

Introduction to hearing audiograms