limitation of sight

Philip Jebaseelan 2 Mozart

Limitations of Sight & Hearing

Overcome Sight and Light Limitations, Page 1


Table of Contents

Introduction In SightPG.3

Introduction In Hearing..PG.4

Limitation Of Sight..PG.6

Types Of Limitations Of SightPG.7

Devices Of Sight..PG.9

ConclusionPG.17

Limitation Of HearingPG.18

Types Of Limitation Of Hearing.PG.

Devices Of Hearing..PG.

ConclusionPG.



Introduction In Sight

Visual perception is the ability to interpret the surrounding environment by processing information that is contained in visible light. The resulting perception is also known as eyesight, sight, or vision (adjectival form: visual, optical, or ocular). The various physiological components involved in vision are referred to collectively as the visual system, and are the focus of much research in psychology, cognitive science, neuroscience, and molecular biology, collectively referred to as vision science.

The visual system in animals allows individuals to assimilate information from their surroundings. The act of seeing starts when the lens of the eye focuses an image of its surroundings onto a light-sensitive membrane in the back of the eye, called the retina. The retina is actually part of the brain that is isolated to serve as a transducer for the conversion of patterns of light into neuronal signals. The lens of the eye focuses light on the photoreceptive cells of the retina, which detect the photons of light and respond by producing neural impulses. These signals are processed in a hierarchical fashion by different parts of the brain, from the retina upstream to central ganglia in the brain.

Note that up until now much of the above paragraph could apply to octopi, mollusks, worms, insects and things more primitive; anything with a more concentrated nervous system and better eyes than say a jellyfish. However, the following applies to mammals generally and birds (in modified form): The retina in these more complex animals sends fibers (the optic nerve) to the lateral geniculate nucleus, to the primary and secondary visual cortex of the brain. Signals from the retina can also travel directly from the retina to the superior colliculus.

The perception of objects and the totality of the visual scene is accomplished by the visual association cortex. The visual association cortex combines all sensory information perceived by the striate cortex which contains thousands of modules that are part of modular neural networks. The neurons in the striate cortex send axons to the extrastriate cortex, a region in the visual association cortex that surrounds the striate cortex.



Introduction In Hearing

Hearing, auditory perception, or audition is the ability to perceive sound by detecting vibrations, changes in the pressure of the surrounding medium through time, through an organ such as the ear. 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.There are three main components of the human ear: the outer ear, the middle ear, and the inner ear.

OUTER EAR : The outer ear includes the pinna, the visible part of the ear, as well as the ear canal which terminates at the eardrum, also called the tympanic membrane. The pinna serves to focus sound waves through the ear canal toward the eardrum. Because of the asymmetrical character of the outer ear of most mammals, sound is filtered differently on its way into the ear depending on what vertical location it is coming from. This gives these animals the ability to localize sound vertically. The eardrum is an airtight membrane, and when sound waves arrive there, they cause it to vibrate following the waveform of the sound.

MIDDLE EAR: The middle ear consists of a small air-filled chamber that is located medial to the eardrum. Within this chamber are the three smallest bones in the body, known collectively as the ossicles which include the malleus, incus and stapes (sometimes referred to coloquially as the hammer, anvil and stirrup respectively). They aid in the transmission of the vibrations from the eardrum to the inner ear. While the middle ear may seem unnecessarily complex, the purpose of its unique construction is to overcome the impedance mismatch between air and water, by providing impedance matching.

Also located in the middle ear are the stapedius and tensor tympani muscles which protect the hearing mechanism through a stiffening reflex. The stapes transmits sound waves to the inner ear through the oval window, a flexible membrane separating the air-filled middle ear from the fluid-filled inner ear. The round window, another flexible membrane, allows for the smooth displacement of the inner ear fluid caused by the entering sound waves.



IINNER EAR: The inner ear consists of the cochlea, which is a spiral-shaped, fluid-filled tube. It is divided lengthwise by the organ of Corti, which is the main organ of mechanical to neural transduction. Inside the organ of Corti is the basilar membrane, a structure that vibrates when waves from the middle ear propagate through the cochlear fluid endolymph. The basilar membrane is tonotopic, so that each frequency has a characteristic place of resonance along it. Characteristic frequencies are high at the basal entrance to the cochlea, and low at the apex. Basilar membrane motion causes depolarization of the hair cells, specialized auditory receptors located within the organ of Corti. While the hair cells do not produce action potentials themselves, they release neurotransmitter at synapses with the fibers of the auditory nerve, which does produce action potentials. In this way, the patterns of oscillations on the basilar membrane are converted to spatiotemporal patterns of firings which transmit information about the sound to the brainstem.



Limitation Of Sight

There are some limitations to the senses of sight and sense of hearing. For example, our eyes cannot see very small objects such as germs while our ears could not hear very small or very strong. However, with the advent of modern technology, obstacles and limitations to the senses as this can also be overcome.

To overcome the limitations of sight, the telescope, microscope and magnifier are used. The telescope let the space scientists to be able to look very distant objects like the moon, so that we know more about space. The function of the microscope is to view very small objects such as microorganisms. It is very useful to the microbiologists. Besides that, the magnifier also can overcome the limitations of sight because it can magnify the small objects.



Types Of Limitations Of Sight

There are several types of limitation towards sight such as:

Optical illusion

The Blind spot

There are also several types of defects of limitation of sight which are:

Astigmatisme

colour blindness

Optical Illusion

An optical illusion (also called a visual illusion) is characterized by visually perceived images that differ from objective reality. The information gathered by the eye is processed in the brain to give a perception that does not tally with a physical measurement of the stimulus source. There are three main types: literal optical illusions that create images that are different from the objects that make them, physiological illusions that are the effects of excessive stimulation of a specific type (brightness, colour, size, position, tilt, movement), and cognitive illusions, the result of unconscious inferences. Pathological visual illusions arise from a pathological exaggeration in physiological visual perception mechanisms causing the aforementioned types of illusions.

Optical illusions are often classified into categories including the physical and the cognitive or perceptual, and contrasted with optical hallucinations.



Blind Spot

A blind spot, scotoma, is an obscuration of the visual field. A particular blind spot known as the physiological blind spot, "blind point", or punctum caecum in medical literature, is the place in the visual field that corresponds to the lack of light-detecting photoreceptor cells on the optic disc of the retina where the optic nerve passes through the optic disc.Since there are no cells to detect light on the optic disc, a part of the field of vision is not perceived. The brain interpolates the blind spot based on surrounding detail and information from the other eye, so the blind spot is not normally perceived.

Although all vertebrates have this blind spot, cephalopod eyes, which are only superficially similar, do not. In them, the optic nerve approaches the receptors from behind, so it does not create a break in the retina.

The first documented observation of the phenomenon was in the 1660s by Edme Mariotte in France. At the time it was generally thought that the point at which the optic nerve entered the eye should actually be the most sensitive portion of the retina; however, Mariotte's discovery disproved this theory.

The blind spot is located about 1215 nasal and 1.5 below the horizontal and is roughly 7.5 high and 5.5 wide.



Devices On Sight

There are different types of devices to overcome the limitations of sight such as:

Microscope

Telescope

Binoculars

Magnifying glass

UltraSound Machine

Periscope

X-ray Machine

Microscope

A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy. Microscopic means invisible to the eye unless aided by a microscope.

There are many types of microscopes. The most common (and the first to be invented) is the optical microscope, which uses light to image the sample. Other major types of



microscopes are the electron microscope (both the transmission electron microscope and the scanning electron microscope), the ultramicroscope, and the various types of scanning probe microscope.

On October 8, 2014, the Nobel Prize in Chemistry was awarded to Eric Betzig, William Moerner and Stefan Hell for "the development of super-resolved fluorescence microscopy," which brings "optical microscopy into the nanodimension

History

The first microscope to be developed was the optical microscope, although the original inventor is not easy to identify. Evidence points to the first compound microscope appearing in the Netherlands in the late 1590s, probably an invention of eyeglass makers there: Hans Lippershey (who developed an early telescope) and Zacharias Janssen (also claimed as the inventor of the telescope). There are other claims that the microscope and the telescope were invented by Roger Bacon in the 1200s, but this is not substantiated. Giovanni Faber coined the name microscope for Galileo Galilei's compound microscope in 1625

Telescope

A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation (such as visible light). The first known practical telescopes were invented in the Netherlands at the beginning of the 17th century, using glass lenses. They found use in terrestrial applications and astronomy.

Within a few decades, the reflecting telescope was invented, which used mirrors. In the 20th century many new types of telescopes were invented, including radio telescopes in the 1930s and infrared



telescopes in the 1960s. The word telescope now refers to a wide range of instruments detecting different regions of the electromagnetic spectrum, and in some cases other types of detectors.

The word "telescope" was coined in 1611 by the Greek mathematician Giovanni Demisiani for one of Galileo Galilei's instruments presented at a banquet at the Accademia dei Lincei.In the Starry Messenger, Galileo had used the term perspicillum".

History

The earliest recorded working telescopes were the refracting telescopes that appeared in the Netherlands in 1608. Their development is credited to three individuals: Hans Lippershey and Zacharias Janssen, who were spectacle makers in Middelburg, and Jacob Metius of Alkmaar. Galileo heard about the Dutch telescope in June 1609, built his own within a month, and improved upon the design in the following year.

The idea that the objective, or light-gathering element, could be a mirror instead of a lens was being investigated soon after the invention of the refracting telescope. The potential advantages of using parabolic mirrorsreduction of spherical aberration and no chromatic aberrationled to many proposed designs and several attempts to build reflecting telescopes.In 1668, Isaac Newton built the first practical reflecting telescope, of a design which now bears his name, the Newtonian reflector.

The invention of the achromatic lens in 1733 partially corrected color aberrations present in the simple lens and enabled the construction of shorter, more functional refracting telescopes. Reflecting telescopes, though not limited by the color problems seen in refractors, were hampered by the use of fast tarnishing speculum metal mirrors employed during the 18th and early 19th centurya problem alleviated by the introduction of silver coated glass mirrors in 1857,and aluminized mirrors in 1932. The maximum physical size limit for refracting telescopes is about 1 meter (40inches), dictating that the vast majority of large optical researching telescopes built since the turn of the 20th century have been reflectors. The largest reflecting telescopes currently have objectives larger than 10m (33feet), and work is underway on several 30-40m designs.



The 20th century also saw the development of telescopes that worked in a wide range of wavelengths from radio to gamma-rays. The first purpose built radio telescope went into operation in 1937. Since then, a tremendous variety of complex astronomical instruments have been developed.

Binoculars

Binoculars, field glasses or binocular telescopes are a pair of identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Most are sized to be held using both hands, although sizes vary widely from opera glasses to large pedestal mounted military models.

Unlike a (monocular) telescope, binoculars give users a three-dimensional image: for nearer objects the two views, presented to each of the viewer's eyes from slightly different viewpoints, produce a merged view with an impression of depth.

History The first binoculars were built in December 1608 for the Assembly of the States General of the Netherlands by Hans Lippershey. He was a spectacle maker from Middleburg in Zeeland and had discovered that a convex lens and a concave lens could be combined to produce a magnified image of a distant object - a simple telescope. Lippershey offered his telescope to the States General on 2nd October 1608, and they requested a version to be used by both eyes, for military purposes. Three sets of binoculars (meaning roughly 'two eyes') were duly delivered but do not seem to have been a huge success with the military, perhaps because they would have had low magnification and poor image quality. Lippershey requested a patent on his invention but it was refused on the grounds



that it was not sufficiently novel. Indeed there is some doubt as to whether Lippershey really was the first to combine two lenses into a telescope. Certainly by early 1609 small 'spyglasses', which we would call telescopes, were widely on sale in Paris. Binoculars however were seldom made because they required much more than twice as much work as a telescope, to manufacture two precisely matched pairs of lenses and fix them in accurate alignment.

Considering that lenses had been available for several centuries, it is somewhat surprising that no-one had discovered the telescope before 1608. Possibly the reason is that to obtain useful magnification the eyepiece lens needs to have a short focal length and thus a large amount of curvature, and lens-grinding technology was not capable of producing such lenses of sufficient quality to yield a clear image.

Magnifying Glass

A magnifying glass (called a hand lens in laboratory contexts) is a convex lens that is used to produce a magnified image of an object. The lens is usually mounted in a frame with a handle (see image).

A sheet magnifier consists of many very narrow concentric ring-shaped lenses, such that the combination acts as a single lens but is much thinner. This arrangement is known as a Fresnel lens.

The magnifying glass is an icon of detective fiction, particularly that of Sherlock Holmes.

History

The earliest evidence of a magnifying device was a joke in Aristophanes's The Clouds from 424 BC, where magnifying lenses to start kindling were sold in a pharmacy, and Pliny the Elder's "lens", a glass globe filled with water, used to



cauterize wounds. (Seneca wrote that it could be used to read letters "no matter how small or dim"). Roger Bacon described the properties of a magnifying glass in 13th-century England. Eyeglasses were developed in 13th-century Italy.

UltraSound Machine

Diagnostic sonography (ultrasonography) is an ultrasound-based diagnostic imaging technique used for visualizing internal body structures including tendons, muscles, joints, vessels and internal organs for possible pathology or lesions. The practice of examining pregnant women using ultrasound is called obstetric sonography, and is widely used.

In physics, 'ultrasound' refers to sound waves with a frequency too high for humans to hear. Ultrasound images (sonograms) are made by sending a pulse of ultrasound into tissue using an ultrasound transducer (probe). The sound reflects (echoes) from parts of the tissue; these echoes are recorded and displayed as an image to the operator.

Many different types of images can be formed using ultrasound. The most well-known type is a B-mode image, which displays the acoustic impedance of a two-dimensional cross-section of tissue. Other types of image can display blood flow, motion of tissue over time, the location of blood, the presence of specific molecules, the stiffness of tissue, or the anatomy of a three-dimensional region.

Compared to other prominent methods of medical imaging, ultrasonography has several advantages. It provides images in real-time (rather than after an acquisition or processing delay), it is portable and can be brought to a sick patient's bedside, it is substantially lower in cost, and it does not use harmful ionizing radiation. Drawbacks of ultrasonography include various limits on its field of view including difficulty imaging structures behind bone and air, and its relative dependence on a skilled operator.

History



Ultrasonic energy was first applied to the human body for medical purposes by DrGeorge Ludwig at the Naval Medical Research Institute, Bethesda, Maryland in the late 1940s.English-born physicist John Wild (19142009) first used ultrasound to assess the thickness of bowel tissue as early as 1949; he has been described as the "father of medical ultrasound". Subsequent advances in the field took place concurrently in several countries.

Periscope

A periscope is an instrument for observation over, around or through an object, obstacle or condition that prevents direct line-of-sight observation from an observer's current position.

In its simplest form, it consists of an outer case with mirrors at each end set parallel to each other at a 45-degree angle. This form of periscope, with the addition of two simple lenses, served for observation purposes in the trenches during World War I. Military personnel also use periscopes in some gun turrets and in armoured vehicles.

More complex periscopes, using prisms and/or advanced fiber optics instead of mirrors, and providing magnification, operate on submarines and in various fields of science. The overall design of the classical submarine periscope is very simple: two telescopes pointed into each other. If the two telescopes have different individual magnification, the difference between them causes an overall magnification or reduction.

History Johannes Gutenberg, known for his contribution to printing technology, marketed a kind of periscope in the 1430s to enable pilgrims to see over the heads of the crowd at the vigintennial religious festival at Aachen. Johannes Hevelius described an early periscope with lenses in 1647 in his work Selenographia, sive Lunae descriptio [Selenography, or an account of the Moon]. Hevelius saw military applications for his invention.

In 1854 Hippolyte Mari-Davy invented the first naval periscope, consisting of a vertical tube with two small mirrors fixed at each end at 45. Simon Lake used



periscopes in his submarines in 1902. Sir Howard Grubb perfected the device in World War I. Morgan Robertson (18611915) claimed to have tried to patent the periscope: he described a submarine using a periscope in his fictional works.

Periscopes, in some cases fixed to rifles, served in World War I (1914-1918) to enable soldiers to see over the tops of trenches, thus avoiding exposure to enemy fire (especially from snipers).

During World War II (1939-1945), artillery observers and officers used specifically-manufactured periscope binoculars with different mountings. Some of them also allowed estimating the distance to a target, as they were designed as stereoscopic rangefinders.

X-ray Machine An X-ray generator is a device used to generate X-rays. It is commonly used by radiographers to acquire an x-ray image of the inside of an object (as in medicine or non-destructive testing) but they are also used in sterilization or fluorescence.

History

The discovery of X-rays came from experimenting with Crookes tubes, an early experimental electrical discharge tube invented by English physicist William Crookes around 1869-1875. In 1895, Wilhelm Rntgen discovered X-rays emanating from Crookes tubes and the many uses for X-rays were immediately apparent. One of the first X-ray photographs was made of the hand of Rntgen's wife. The image displayed both her wedding ring and bones. On January 18, 1896 an X-ray machine was formally displayed by H.L. Smith.

In the 1940s and 1950s, X-ray machines were used in stores to help sell footwear. These were known as fluoroscopes. However, as the harmful effects of X-ray radiation were properly considered, they finally fell out of use. Shoe-fitting use of the device was first banned by the state of Pennsylvania in 1957. (They were more a clever marketing tool to attract customers, rather than a fitting aid.)



Conclusion

Sight is very important for human being to ensure their survival. With sight, human being and animals can differentiate danger from other animals and enemies from human beings facial expression or even by physically actions presented.



Limitation Of Hearing

Every living being on earth has hearing ability. The definition Limitation Of Hearing is the range of sound that each individual such as human beings can hear.Human beings can hear up to 20-20000Hertz. Limitation of hearing varies with each human being.

The range of hearing in each individual lies on ones age, given an example, children have better hearing than adults. This is because childrens eardrums are much more elastic which leads to better hearing. As People slowly age, their hearing deteriorates and also their eardrum becomes less elastic. Therefore, the range frequencies that they can detect decreases. Sum up to that, the hearing of high pitched voice also decreases. A person who is exposed to very loud noises is prone to experience a loss of hearing range of hearing is smaller than normal people.



Types Of Limitation Of Hearing


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