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This article throws light upon the top seven aspects of sensory development in child during first year. The aspects are: 1. Vision 2. Hearing 3. Olfaction 4. Gustation 5. Thermal Sensitivity 6. Pain 7. Static, Kinesthetic Sensitivity.
Sensory Development: Aspect # 1.
Vision:
In the human embryo, the development of the essential neural mechanism begins during the third week of prenatal life. When the infant is born, the neuromuscular apparatus involved in the vision does not happen to be perfect.
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Important studies have been conducted on the responses to visual stimuli; and, the facts revealed may be summarised as under:
(i) The pupillary reflex:
The child contracts its pupil in response to light; it is a reflex action that needs no learning but occurs automatically. At birth, this response happens to be sluggish but perfection in this response is achieved in the first few weeks of birth.
(ii) Visual pursuit:
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In the beginning, a child cannot concentrate its vision on an object; but soon he develops response to this effect.
Though a change of vision, from one object to another in a quick movement, does not happen to be a possibility till the child is about 16 weeks old, yet visual pursuit movement may be marked in a child who is about 15 days old, especially in case, where the stimuli are some nearing coloured spots or some such a thing.
(iii) Co-ordination of the two eyes:
We may have seen that the neonate, for many days after its birth, cannot look at an object with both eyes concentrating immediately upon it as soon as it is brought to its vision—proper co-ordination of the two eyes develops in 7 or 8 weeks’ time when the convergence or binocular fixation becomes “smooth and continuous”; though convergence “in a series of jerking movements” starts occurring even after a few hours of birth.
(iv) The ciliary muscles:
The ciliary muscles of the neonate do not happen to be mature enough so as to catch images properly. But gradually, as the child grows, these muscles also develop the functioning of the eye, goes on improving rapidly.
Fantz found in his experiments that up to about 15 weeks after birth, the preference of the child continued to be for complex patterns, such as a checkerboard or a bull’s eye; simple structures, such as a circle, a square or a triangle, rarely diverted his gaze to look at them.
Nearly up to 8 weeks of time, between a striped pattern and bull’s eye, the preference of the infant was for the former, but after 8 weeks the preference was shifted to the bull’s eye.
In an experiment, three faces were shown to 49 infants, of ages from 4 days to 6 months, to mark their reactions to these three different stimuli. It was found that the infants looked longest at the real face, somewhat less at the scrambled one, and the third face which was no better than a black patch, was typically ignored.
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From this, it can be concluded that the unlearned preference of the child is always for the complex or varied patterns, rather than for “simple and relatively homogeneous stimuli”.
An infant’s visual apparatus matures very rapidly. To assess the visual acuity of a child, an object of his preference will have to be used.
Through experiments, it was found that as a baby grew in age, the visual acuity developed to such a level that a six month old child, from a distance of 10 inches, could concentrate his vision on a stripe that was only 1/64 inch in width—the experimenter had been decreasing the width of stripes as the child was growing in age.
An infant avoids a stimulus of sudden increase in depth. A terrestrial animal would avoid the side which has a sharp “drop-off or cliff; likewise an infant, 6 months old, also avoids a surface which has a sudden dropping down depth.
There are some animals who have a capability of depth perception from the very first day; the chicken and the goat are such animals. So, in the end, it can be summed up that some aspects of visual perception are unlearned, while others develop early during the first year.
Sensory Development: Aspect # 2.
Hearing:
At the time of birth, the hearing mechanism happens to be sufficiently well developed to be functional. Even then, nature protects the neonate in case there is a sudden onslaught of a very loud sound—the mid-ear mucus, or obstruction of the external auditory canal, works as protector. Poor hearing during the early natal days may be there because of these reasons.
Sounds, lasting longer, have greater effect than those which are of very short durations such as for a second or so. A sound which lasted for 15 seconds, elicited more bodily movements, caused faster respiration, and closing of eyelids. If the sound continued for duration much longer than this, first there was response which later on subsided because of such a long duration of the sound.
Loud sounds proved stronger stimulants and elicited more bodily movements, closing of eyelids, and changing of respiratory rates. Bridger in an experiment on 50 neonates, ranging in age between 1 to 5 days, found that they responded differently to different frequencies.
“A tone of a given pitch was sounded repeatedly until babies ceased responding to it”, and then, the pitch of the tone was changed, though the loudness was the same, and there was a response; bodily movements were increased, and there was also increase in the rate of heart palpitation.
Sensory Development: Aspect # 3.
Olfaction:
The investigators found that the little babies responded differently to pleasant and unpleasant smells. The neonate would suck its thumb when there was a pleasant odour, such as that of anise oil. It turned away its head, and made grimaces, when the smell was unpleasant. If there was a greater saturation of odours, the baby would make more movements.
Sensory Development: Aspect # 4.
Gustation:
The experiments found that the neonates did not give any indication of having felt any difference in taste among solutions of different kinds, that is, that of sugar, salt, citrate, and so on, when applied to their tongues— so poor happens to be the taste sensitivity in the beginning.
However, a two weeks old child made clear, positive (sucking) response to sugar, and negative (grimacing) to quinine and citric acid. The experiments were conducted by Pratt KC et al. Another investigator found “a moderately full baby is a better discriminator than the very hungry infant.”
Sensory Development: Aspect # 5.
Thermal Sensitivity:
The neonate becomes more active when it is colder, but the activity level is reduced when the object touching its leg is made hotter by 5 to 6 degrees from a neutral point of 33 °C. Cold stimuli (11°C or 12°C below the neutral point), when applied to the legs, increased head movements, accelerated breathing; and irregular pulse followed when stimulation was applied to the forehead.
It was also found that milk warmer than 50°C, colder than 23°C made the infant squirm and suck irregularly. Of course, in this respect also individual differences are found.
Sensory Development: Aspect # 6.
Pain:
There is no localised area in the brain which can receive and integrate pain producing stimulation. Learning plays a significant role in this respect. Pain sensitivity happens to be present in some degree even at the time of birth, but it grows sharper during the first few days.
Number of pain stimuli decreases during the period from birth to 8 days but the sensitivity grows sharper. Constitutional differences, of course, are found there. A female child is more sensitive to the stimulation of pain; the more sensitive to the stimulation of pain one is, the more susceptible to the feeling of fear and anxiety he would be.
Sensory Development: Aspect # 7.
Static, Kinesthetic Sensitivity:
If a neonate is held upside down, or jarred, or its spatial position is changed, it will make generalized postural adjustment. Body rotation or prone placement on a table, may stimulate nystagmus (oscillation of eyes).
If the infant is held upright with its feet resting upon a flat surface, it would alternate stepping. Thus, from the very beginning, the child has the tendency of maintaining upright posture; this tendency proves helpful in enabling the child to walk in due course of time (Fig. 4.3).
