CHAPTER 5 CHANGES IN HEIGHT AND WEIGHT The average newborn weighs 7 1 2 pounds and measures about 20 inches from head to toe In the next two years the infant will grow faster than at any later period including adolescence Birth weight typically doubles by five months to 15 pounds and triples by the first birthday to 22 pounds The baby gains only 5 to 6 pounds in the second year and 4 to 5 pounds in the third year Height increases by about half in the first year to 30 inches and by an additional 5 6 inches in the second year Despite the overall rapid growth during the first two years the rate of growth tapers off from the first to the second year It has been shown that a babies tend to grow in spurts rather than in an even progression Lampl et al 1992 For example a baby might not grow at all for several days or weeks followed by sudden growth of up to an inch in 24 hours Childproofing central nervous system CNS of which the brain is a part 250 000 new nerve cells each minute resulting in approximately 100 billion nerve cells in the newborn fundamental structure of the nervous system is designed to manage the storage and transfer of all of the information necessary to support the biological functions of bodily systems and the psychological functions of sensation perception learning and intelligence Nerve cells do not actually touch each other but adjoining cells form a microscopic gap called a synapse which is structured to allow Impulses to be conducted from cell to cell by chemicals known as neurotransmitters Synapses begin to develop in very large numbers prenatally and continue to increase in extraordinarily large numbers through the first 3 years of life in a process called synaptogenesis 1 000 trillion synapses in the nervous system 50 more than in the adult brain at end of third year If one part of the nervous system becomes damaged or unable to function other parts of the system will be able to take over We refer to this as the plasticity of the human brain Synapses and cells that are not stimulated are eliminated through a massive and continuing destructive process know as pruning begins at 2nd year continues to 10th year PERCEPTION Visual Tests visual preference method the researcher presents pairs of stimuli to the baby The researcher observes the infant from a hidden vantage point between the two stimuli detects which stimulus the infant is looking at by the reflection of the fixated stimulus on the pupil of the infant s eye and records changes in fixation method of event related potentials electrodes are attached to the scalp of the infant to measure changes in electrical activity in the brain in response to changing stimuli presented to the infant Variations in brain wave patterns to different stimuli are interpreted as indications that the infant has perceived the stimuli as different habituation dishabituation procedure researchers take advantage of the fact that like adults infants react to changes in sound smell taste or visual display by staring blinking ducking reaching or blushing and or by changes in heart rate and respiration As a particular stimulus is repeated over and over at the same intensity infants habituate to the stimulus the intensity of their responses steadily decrease When habituation has lowered the response rate to about one half of the original level the researcher introduces some subtle change in the stimulus and records corresponding changes in the infant s responses If the infant does not alter his or her behavior to the change in stimulus the researcher concludes that the change was not perceived However if the infant changes response or dishabituates the researcher infers that the child has discriminated the change in the stimulus high amplitude sucking technique Siqueland Delucia 1969 researchers use of a special pacifier with an internal sensing device that indicates when the infant s rate or intensity of sucking increases An increase sucking activates a device that generates a visual or auditory stimulus If the infant likes the stimulus it keeps sucking if not it will decrease its sucking Visual Development retina a complex layered tissue on the back surface of the eye made up of light sensitive cells and nerve cells fovea a densely packed set of highly sensitive cells at the center of the retina can discriminate the detail necessary to perceive objects Since the retina and the fovea are not mature at birth infants visual acuity or sharpness of vision is quite low The eye must also learn to use its ciliary muscles to bend or focus light waves reflected off objects at varying distances toward the fovea infants develop smooth pursuit movements that enable them to track the movement of objects in space Once the infant has learned to explore the external contours and internal contours of objects the stage is set for differentiating objects out as separate entities Historically psychologists have referred to this as the problem of separating the figure from the ground or the object from its background Infants must learn to process three types of visual information Binocular information derives from the different locations of the two eyes in the head Each eye views nearby objects from a slightly different angle thus producing two slightly different retinal images The infant must learn to blend these slightly discrepant views into a single image and to estimate the distance of the object The infant s ability to interpret binocular cues is reasonably well developed by about four months kinetic information When the infant s head moves from side to side the image of a near object moves more rapidly across the retinal surface than the image of a more distant object The infant s ability to detect and interpret this difference emerges slowly during the first months life visual cliff distance cues are also provided by pictorial information Photographs though they are flat give various pictorial cues that create the impression of three dimensionality perspective objects of equal size are judged closer or farther away by their relative size in a picture and superimposition objects that block out the view of other objects are judged to be closer The ability to process pictorial depth cues develops between 5 and 7 months AUDITORY PERCEPTION OTHER taste and smell REFLEX BEHAVIORS reflexes involuntary stimulus response patterns reflexes are controlled by clusters of cells within the brain stem located at the upper end of the spinal cord just below the
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