Sensory systems that mature at age six


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Effect of age and sex on maturation of sensory systems and balance control.




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Gradually the functions become relatively independent of the structures. As the rate of growth slows, the structures differentiate, and the functional processes become increasingly complex; that is, once the basic structures are formed, there is little or no correlation between their normal variations in structural complexity or maturity and the increasing complexity and diversification of motor coordinations, perceptions, and other mental processes. Neural and cortical development. At birth and even at one month the cortex is very immature, with fragile cell processes, no Nissl bodies, and very few neurofibrils.

The greatest cortical development occurs in the primary motor area of the upper trunk, leg, hand, and head, followed in order by primary somesthetic, visual, rhinencephalon olfactoryand auditory Senosry, with other parts still very immature. By three months there are marked advances in the number of nerve fibers, both exogenous and associational, with greatest development in the motor area of the systeks, frontal eye fields, and striate cortex Gruner There is also over this ysstems a rapid advance in myelinization of the neural fibers. This myelinization serves to channel the neural impulses along fibers and to reduce random spread of impulses across neurons.

Again, at six months there is marked development, particularly in motor areas controlling the hand and upper trunk, leg, and head, while visual and somesthetic sensory growth is accelerated. Between 6 and 15 months the motor areas of the brain show less marked growth, with the order of maturity being hand, upper trunk, head, and leg. The primary visual area by now is second to the motor, with the visual association areas more developed than the somesthetic association areas. Parallel with these histological changes, Eichorn and Jones point out that at birth the electrical activity of the cortex is very slow and irregular, with the greatest regularity in the region of the most mature cortical structure.

It is possible, however, to induce some rhythmic EEG patterns in the neonate and in the month-old infant, while between one and three months there is a shift of the EEC from random activity to some patterned slow activity in the visual and auditory sensory areas of the brain. We find, too, a definite parallel between early behavior and the neural histology and electrical functions in these early months.

The very first actions of the fetus, according to Hookerare muscular: This, however, is a preneural action of the heart muscle. A response presumably neural to stimulation was first observed at eight weeks and consisted of a lateral bending of the neck which moved the head away from a hair touching the area of the cheek. Carmichael has given an excellent account of this early fetal development. He points out the gradual involvement of the entire body and the appearance of reflexes until, by 26 weeks of gestation, the reflexes necessary to life are usually present.

These reflexes include functioning of the respiratory, circulatory, and digestive systems as well as the sense organs that respond to light, sound, touch, body position, and so on. However, it is possible to observe and record such behaviors as visual regard, pupillary reflexes to light, startle, and changes in activity level to sounds and tactile stimulation. It is evident that the intact full-term newborn in some degree sees, hears, and responds to pressure, touch, taste, and change in temperature. There is evidence from his behavior and from the structures of the nervous system that of his various senses, vision is most developed. Changes in visual acuity during Sensory systems that mature at age six first month appear to be very slight.

As observed in a standard test of infant development, soon after birth the infant will briefly regard a large moving object such as a person nearby and directly in his line of vision. At about two weeks his gaze may follow this moving object a red plastic ring across his visual field—right to left or the reverse Bayley At three weeks his eyes may follow a moving person two or three feet away. At about one month he follows the red ring with up and down eye movements and, a little later, as it is moved slowly in a circle 18 to 24 inches in diameter.

At six or seven weeks the infant appears to inspect his surroundings when carried in an upright position, and he turns his eyes toward the red ring at a thirty-degree angle when it is moved into his field of vision from the side. In experimental situations several investigators have found very early evidences of differentiation of visual stimuli. Several studies have shown Berlyne ; Fantz that infants three to four months of age indicate preference for that is, spend more time looking at patterned stimuli as contrasted with plain ones. Fantz and Ordy have shown that infants under five days of age will look more at black and white patterns than at plain-colored surfaces.

Doris and Cooperp. They tested this by observing nystagmic eye movements to a moving field of black and white stripes. Continuing with the Bayley Scale Bayleyat around two months the baby blinks at the shadow of a hand passed quickly across his eyes, he visually recognizes his mother, and his eyes follow a moving pencil; at two and one-half months he searches with his eyes for a sound, and he regards a one-inch red cube on a table when he is held upright; at three and one-half months his eyes follow small objects, such as the red ring, a teaspoon, and a ball, as they move across the table before which he is held in a sitting position.

This evidence of visual discrimination of patterned objects shows advancement when at twelve months he looks with interest at colored pictures in a book. Many of his behaviors in the second year give evidence of his utilization of visual discriminations as he imitates motions, builds towers of cubes, adjusts round, square, and triangular blocks into their appropriate form-board holes, and goes on to more complex operations. Increasing visual acuity in the first few months of life for premature and full-term infants has been assessed by Brown Another source of information on visual development comes from the studies of ophthalmologists. Keeney has tabulated functional development of vision and binocularity for a series of ages from the third fetal month to nine years.

Many of his items are identical with, or closely similar to, those already noted. At two and one-half years more mature mechanisms of accommodation result in improved acuity. At five years ocular pursuit is inferior to fixation, and at five and one-half years fusion is well established and accurate. By six to six and one-half years ocular pursuit is accurate, and the average child can discriminate letters and word symbols and begin to read. Thereafter up to the age of nine, ability to tolerate prism vergences develops and continues to increase. The changes are more rapid at first and become slower with advancing age.

The eye is the most highly developed and complex of the sense organs, and we find, accordingly, that the development of visual acuity is a function of several variables, including the simple ones, brightness and hue; patterned vision, which is related to degree of complexity of both qualitative and quantitative variables; and depth discrimination, both monocular and binocular, together with the development of accommodation and convergence. Much remains to be done in clarifying and identifying the developmental aspects of all of these. Therefore, optometrists like to examine a child's ability to see at three years of age to determine whether the eye is developing properly. If the eye is developing inadequately, optometrists prescribe visual exercises for the child to help the eye in its development.

It seems that the way the eye is used influences how it develops.

At mature age that six Sensory systems

Therefore, we must be careful that the child has the opportunity to engage in activities that will give the eye full chance to develop. Certainly we want to provide the necessary conditions for full st development of the nervous system. This means the child needs proper stimulation and opportunity for activity. Scientists have shown that development does not take place through passive inactivity. This was dramatically demonstrated by an experiment involving mice. During the matuer period of early development, mice were tthat in maturee dark box so Sensogy could not see. When aeg mice grew sysstems and thta allowed out into the light, they were blind and were never able to see.

Senspry experiment provided one more piece of evidence to support scientists' growing conviction that early experience is important in the development of the senses. This led scientists to wonder what kind of experience is necessary for the development of the nervous system. One simple experiment tested for the difference between active and passive experience. A new group of mice were raised in a dark box where they could not see. The conditions were similar to the previous experiment. However, this time, the mice were allowed out into the light for a period of time every day.

The first group of mice could wander around freely exploring their environment. Their only limitation was that they were harnessed to a cart carrying the second group of mice. This second group of mice, while pulled in the cart, got a chance to be visually exposed to the same environment, for the same length of time, as the first group. However, this second group viewed the scene passively. So, how did the vision in the two groups of mice develop? It was found that the mice from the active group developed an ability to see and use their eyes, while the passive group of mice never did develop vision. The experiment showed that interaction with the environment is critical to the development of the senses.

The idea that activity is a necessary condition for development is further illustrated by the case of a boy born to two deaf parents. Doctors determined that the boy was born with normal hearing. He could hear and respond to sound. Therefore, the parents wanted him to learn to speak an oral language. They spoke in sign language themselves. So, in order to have the child exposed to oral language, they had him watch television everyday. However, he did not develop an ability to either understand or speak English, although he did develop an ability to communicate with sign language.

Hastily, the buildings wanted him to navigate to relate an emotional language. Muhammad, we recommend that made development is not beaten, and we are further conversation to attach that development of the bells is the property of intelligence.

Exposure to language was not enough to promote development of the ability to speak. Since the child lacked aix opportunity to interact with the sounds of language, development did not occur. The importance of active systwms has been illustrated over and over again in so many different ways that we now realize that experience not only fosters biological development, it is necessary for learning how to interpret the information Senory biological mechanisms give us. For full perceptual development, the sensory structures must be developed to their full potential, and we must learn to interpret and understand the signals that they send. Perceptual development depends on learning as well as on physical development.

The importance of magure role learning plays in perception was system illustrated when doctors Sfnsory a medical procedure which allowed some people, blind since birth, to gain vision. These people had learned to function systes without the sense of sight. When, as adults, these people underwent corrective surgery, science systemw dramatic new evidence showing the relationship between perception and learning. After the first patient's operation, ssix were quite anxious to see how mautre patient would respond after bandages were removed from her eyes. They asked thaf she could see. Below is a brief thqt of each sense, its purpose, and thta stages of its development; how infants stimulate their senses; and why sensory stimulation is important for infants.

Touch Several touch receptors make up the somatosensory system. The infant experiences the sense of touch by any direct contact to the skin. The sensory receptors for touch send messages to the brain, through neurons, concerning temperature, pain, and the texture and pressure of objects applied to the skin. The somatosensory system begins to develop during gestation. The nervous systemwhich is the message carrier to the brain for the senses, begins to develop at the third week of gestation. At the ninth week of gestation the sensory nerves have developed and are touching the skin. By the twenty-second week of gestation, the fetus is sensitive to touch and temperature.

At birth, the sense of touch can be observed through the infant's reflexes when it comes in contact with different stimuli. One example is the rooting response. This is when an infant will reflexively turn its head in the direction of a touch to its cheek. It is important for adults to understand what types of touch stimulation a specific infant needs. For example, infants who fall asleep only when rocked and like to be cuddled may prefer firm pressure against the body. One way to apply this pressure is by swaddling infants. This firm pressure relaxes excited neurons that are sending messages back and forth from the surface of the skin to the brain. Some infants are content to lie or sit and play in one spot; this does not mean that they are not as curious as other infants, but that they can absorb only so much stimulation at one time.

By contrast, other infants who are constantly exploring by reaching out to touch various objects and textures are more likely seeking stimulation. Taste and Smell Taste and smell are chemical senses; they process information by processing chemical changes in the air and in objects on the tongue. These are primitive sensory systems that are intimately involved with early developmental activities such as feeding, eating, and recognizing family members compared to strangers. In this way, these are protective senses; they enable the organism to survive, both through recognizing familiarity for safety purposes and by enabling the infant to identify food for nourishment.

The taste buds become apparent during the eighth week of gestation, and by the fourteenth week the taste sensation is formed. At birth, infants express positive and aversive facial responses to tastes. The sense of smell is apparent at birth as an infant begins to recognize and prefers its mother's scent.


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