Are parents ready to red shirt there children? No, I'm not talking about sports but kindergarten. Many parents are facing the issue of whether or not their children are ready for the big step into the classroom. Before entering kindergarten children need to develop their perceptual skill (depth perception). As humans we need depth perception for detection, discrimination, and identification of objects. Depth perception is a difficult topic to access due to the fact that the world is three dimensional and human visions are two dimensional. When transmitted to the brain, an image on the retina is not a picture; rather it is a pattern of nerve impulses, aroused by a light pattern that terminates in the visual area of the cerebral cortex.
Through some activity of the occipital lobes of the cerebral cortex, human beings apparently perceive the external world in a three-dimensional manner that is correlated with the retinal-image pattern in some orderly manner. Psychologists are particularly interested in the cues which enable people to perceive depth and distance. Stimulus patterns for arousing a depth experience occur when individuals are given specific cues. The cues may be monocular, effective when using one eye as well as two, or binocular, requiring the usage of both eyes. The cues may also be psychological, depending only on the visual image, or physiological, originating from the structure and movement of the eyes. In this paper I will explain perceptual development and how it relates to animals, infants, and blind infants.
Infancy is the period of life in which development occurs most rapidly. Development occurs in a variety of different ways and has been categorized with the study of infancy into physical, motor, and perceptual development. Each of these forms of development occurs simultaneously and progress in each facilitates the progress of the other. There are many studies I will assess to further explain how they contribute to explaining the development of perception. In developing direct perception one must be able to directly perceive what the objects and surfaces in the environment are perceived as an action of afford ances.
An example of an is stair climbing. Walking down a flight of stairs as an 18 month and adult are different. As an individual grows, perception of afford ances might change. When climbing the stairs a person must be able to judge leg length to judge how they climb the stairs. Oculomotor and visual cues help us solve this problem as sources of depth perception.
Oculomotor is broken down into convergence and accommodation. The amount of convergence and accommodation can be used as cues for absolute depth (for objects not too far away from you). Visual cues can be broken down into binocular and monocular. Binocular visual fields make use of binocular depth cues; an organism must have a binocular visual field -- a region of overlapping visibility for the two eyes. Different animals have different extents of binocular visual fields. In general, predators have both eyes on the front of their heads, and consequently have large binocular visual fields.
In contrast, prey typically have one eye on either side of their heads, and consequently have small, if any, binocular visual fields. The visual system uses disparity information as one cue to depth. The fact that a three-dimensional percept can be derived from retinal disparity is seen when we view stereogram displays in which each eye receives a slightly different picture / view. In the 1830 s, Wheatstone developed a device with which to view stereogram: the stereoscope. This device presented one two-dimensional view of a scene to one eye, and a slightly different two-dimensional view to the other eye. When the brain received these slightly different views from the two eyes, it integrated them into one three-dimensional scene.
In other words, the disparity between the two scenes enabled the observer to see depth. Perceptual development means how animals and humans alike develop their seeing capabilities. This development of perception could be learnt or innate. This concept of perceptual development is heavily based from an old issue in psychology, the nature vs. nurture. We have to wonder, stated by Walk in The Development of Depth Perception in Animals and Human Infants, "Do we learn to the world about us, or do we see the world in all its complexity innately, without any learning?" The question of whether individuals learn or inherit the ability to interpret these cues is a persistent controversy among psychologists.
Some psychologists maintain that human perceptions of space, at least to a certain extent, are sensed directly by visual cues beginning at birth. Research involving a visual cliff shows that, by the time infants are crawling, they already avoid tumbling off a visual drop off. Some animals, born with open eyes and walking ability, also avoid visual cliffs, apparently without 'learning.' It is, of course, difficult to prove that this behavior is not learned, since both animals and human infants are exposed to an environment involving depth and space before they can be tested on the visual cliff. Some psychologists contend that the process of defining and using visual cues results from our learning about the world through our other senses. People may learn to interpret these cues through associated tactile and motor processes. For example, an object looks round because it feels' round, or an object looks nearer to someone because the muscular effort used to touch it is less than the effort expended reaching for an object that looks farther away.
One psychologist has written that this type of learning is not an either-or proposition, because innate organization and acquired meaning may both be involved. Many theorists found perception as a predecessor to both movement and cognition and projected that children with learning disabilities lacked perceptual development. An example of this is being able to perceive the difference in spatial orientation between a circle and line, and the difference between the form of a letter b and the form of letter d. If a child lacks perception reading may become complex. Many theorists hypothesize that deficits could be re mediated by perceptual-motor activity programs.
By implicating these programs perceptual motor responses, children could overcome perceptual and cognitive difficulties. Animal studies allow us to do things that we could not do to human infants, and see what effect our manipulations have on the animal's development. Animals like babies are unable to tell us what they perceive. I will explain the concept of development of depth perception in chick and kittens. Conditions in 1873 done by Spalding in Instinct with Original Observations on Young Animals, was the first controlled observation of distance perception in animals. He held a chick in a black flannel bag after it was hatched and observed the chick going to its mother even though there were obstacles in its way.
This was a control to ensure that animals were relying on vision and not sound. In 1957 Walk, Gibson, in The Visual Cliff, used a visual cliff apparatus and animals that had no previous visual experience. The animal was placed in the center of glass. On one side of the center board, a texture surface was just beneath the glass which was considered the shallow side. On the other side there was no textured surface under glass but could see a textured surface a distance below which was considered the deep side. In 1960 Gibson and Walk combined and tested day old chicks on the same visual cliff, and found that evidence of depth perception in chick is present at birth.
However, in 1963 a study by Nealey and Riley kept animals in the dark for 300 days. On their emergence from the dark, their depth perception was absent. Two years later Walk, Try chin, and Karel found lack of depth perception past 140 days in the dark. But depth discrimination returned with experience in the light.
When a cat extends its forelimbs automatically as if to prevent collision this is called visual placing. Visual placing is common in all mammalian species, and is used to examine depth perception in animals. Working with kittens, Riesen and Aarons in 1959 showed that visual placing response was absent in kittens reared for six weeks in the dark. Gibson and Walk furthered Riesen and Aarons study and showed that a 4 week old kitten discriminates depth on a visual cliff model, and a dark reared 4 week old animal does not. Gibson and Walk findings confirmed that they found the visual placing absent in dark reared animals. One of the most famous studies done with Kittens was when theorists Held and Hein in 1963 studied early motor activity in kittens.
The purpose of this study was to understand if perception is learnt or is an innate process. They deprived some newborn kittens of motor activity while permitting others to move. They kept the visual experience identical for all kittens having them in a kitten carousel. One of the pair of kittens was harnessed but could walk around (active kitten) while the other kitten was restricted from moving (passive kitten). The passive kitten later failed to accurately judge depth perception and failed paw placing and eye blinking, when an object approached.
The active kitten developed both visual placing reaction and depth discrimination on the visual cliff. With this study you can conclude that kittens do not show perception of depth at birth and is learnt in kittens. Held and Hein concluded that it wasn't that the kittens actually failed to learn about depth cues, but it was that they failed to learn the correct motor responses associated with them. This study provides more evidence that at least some visual abilities have to be learned through experience; in this case experience of locomotion around one's own immediate environment. Three conclusions from animal studies is that first, depth perception is innate in some species, such as the chick. The second conclusion is that depth perception must be maintained by light stimulation in all species.
The third conclusion is that the development of depth perception in some species, such as the kitten, is dependent on an interaction of innate factors and environmental stimulation. With human infants Gibson and Walk used the visual cliff apparatus which was used in animals. Gibson and Walk suggested that avoidance over the visual cliff was instinctive. Human infants when called by their mother on the opposite side refused to crawl out on the glass covering drop-off. Campos and his associates in 1971 had a different thought; he believed that avoidance behavior in human infants is not instinctive.
Campos argued that avoidance develops as a consequence of experience loco moting. His explanation lies in a re afferent theory of perception whereby feedback correlates with self produced movement is seen as necessary to produce appropriate visually directed behavior. In 1978 Campos examined the heart rate response to the visual cliff with age. He used infant from 2, 3. 5, and 5 months old who showed a significant heart rate deceleration when placed on the glass over the apparent drop off, or deep side.
While infants of 9 months showed an acceleration of heart rate on the same deep side. Deceleration of heart rate is most often taken as evidence of interest, while acceleration is taken to be evidence of fear. It was recorded that there was a positive correlation with an increase in age between the crawling experience and latency to reach mother on deep side. In this study heart rate only shows a relationship between age and fear of the deep side of the visual cliff and not between loco motor experience and fear. When an infant is placed in the center of the visual cliff it is relying on feedback. Feedback is known to have at least three aspects: internal feedback that signals an intended action within the nervous system, this occurs prior to overt action.
Feedback proper form the effectors system during action, and knowledge of results that may occur only after action has been completed. It is important for infants to have good relation of body movements with hands and legs, for infants it allows them to learn the emergence of their new tools. Infants given experience in a walker failed to avoid the cliff when tested. These findings with the walker went against the finding in the reaffernet theory of avoidance behavior.
Infants were tested on the visual cliff's shallow and deep sides in the walker and while crawling. The subjects tested in the walker first and the other half tested crawling first. Analysts show that when infants learn to crawl is the best predictor of when the child will avoid the deep side of the visual cliff apparatus when crawling. In this study children that cross the visual cliff learned to crawl before 6. 5 months. While, those who avoided the cliff had learned to crawl at or after 6.
5 months of age. This study proved that the amount of crawling experience predicts avoidance behavior. One problem with this study is that having babies in the walker they feel safe, and for some reason ignore the significance of the cliff study. As well as if crawling begins before 6. 5 months crawling is not as responsive to visual information specifying a drop-off. Having an infant who crawled before or after 6.
5 months may relate to the sensitive periods during human development. The concept of sensitive period is fundamental to understand the effects of early experience in development. A developing organism is subject to the effects of specific forms of experience and outcomes in the form of significant structural and functional changes that are resistant to change at later ages. The basis of the sensitive period is the neurophysiological process in intrinsic generation of an excess number of synaptic connections among neurons. Development of these synaptic connections survives while others do not. The determining factor of if they survive is if those synapses are activated by sensory or motor experience, while others are lost through disuse.
Infant's visual mechanisms are still maturing and in return an infant can be coaxed across a deep side under the condition of a cliff study. In 1961 Frantz has reported that infants 3 to 5 months of age fixate stripes of 5 to 10 minutes of visual angel in preference to gray, a preference for stripes of 1/32 to 1/64 inches at 10 inches distance. The performance in the visual cliff may be affected because it weakens the acuity mechanisms. These studies aim to find out whether we can adapt to a consistent change in our visual array. This would show that we are able to adapt and have more evidence that perceptual ability is learnt, whereas a failure would support the assertion that perception is innate. Stratton inverted his vision with lenses in 1896 and found that he was soon able to adapt and carry out complicated procedures like writing and pouring drinks with ease, although better with his eyes closed.
Most human subjects are able to adapt after a short period of disorientation, significantly better if they moved around. This implies that human perception is learnt and that the motor system plays an important part with perception depth. Having two stimuli a deep side appearance and shallow side appearance on the visual cliff increases shifting. Shifting is when human infants are presented with two visual displays; they often alternately fixate the two. An increase in shifting in the two conditions of greater similarity suggests that infants are able to process information collectively and separately. Increasing the similarity of the two stimuli in a pair would lead to in habituate to the common aspects of both stimuli at the same time.
The more unfamiliar the stimuli or the fewer features they have in common, the more likely that they would fixate on the second stimulus, longer looking at that side. Perception is also important by differentiating the perception of surfaces. In 1987 Gibson et al examined infants with crawling experience and walking experience with a rigid surface (cloth over plywood) and a deforming surface (cloth over a waterbed. ) All of the infants traversed the surfaces, but the walkers hesitated to cross the deforming surface. The walker examined the deforming surface both by vision and touch, and then crawled over the surface.
Crawlers showed no preference of any surface, but walkers showed preference to the rigid surface. Experience in interacting with the world is vital to perception. For instance, with the Held and Hein in 1963, Movement-produced Stimulation in the Development of Visually Guided Behavior, kittens raised without visual experience or deprived of normal visual experience do not perceive the world accurately. In one experiment, researchers reared kittens in total darkness, except that for five hours a day the kittens were placed in an environment with only vertical lines.
When the animals were later exposed to horizontal lines and forms, they had trouble perceiving these forms. Philosophers have long debated the role of experience in human perception. In the late 17 th century, Irish philosopher William Molyneux wrote to his friend, English philosopher John Locke, and asked him to consider the following scenario: Suppose that you could restore sight to a person who was blind. Using only vision, would that person be able to tell the difference between a cube and a sphere, which she or he had previously experienced only through touch? Locke, who emphasized the role of experience in perception, thought the answer was no. Visual experience is useful because it creates memories of past stimuli that can later serve as a context for perceiving new stimuli. Thus, you can think of experience as a form of context that you carry around with you.
How does perception and motor abilities develop in a child who has been blind since birth? Usually in blind children loco motor milestones are delayed compared to normal population. In the study by Norris et. al in 1957 a group of 66 children blind from birth and neurologically intact, only 50% were walking independently at 24 months. In Gross Motor Development in Infants Blind by Birth by Adelson et al in 1974 studies 10 infants, blind from birth and showed neuromuscular maturation and postural achievements. From the findings with these infants, it was found that blindness does not affect gross motor development. Blindness has little impact upon postural achievements in blind and normal infants.
One dilemma in blind infants is that there is a delay in self initiated mobility, that vision may play a central role in the achievement of mobility and posture. Only after an infant receives experience in reaching on sound will it begin to creep, walk, and slowly map the concrete world around him. In 1971 Freedman and Can nady in 1971 found significantly greater delays in infants who had suffered severe environmental deprivation than in infants who were blind from birth. From reading these studies there are two theories that I think should be looked at more closely and examined. With relation to the animal studies with the chicks born with depth perception, maybe this had some relation to the amount of time a hen is pregnant with a chick. However with infants depth perception is learnt.
Does the amount of time in the womb effect depth perception in human infants. With the chicks when exposed to light for a certain amount of time depth perception was learnt. If possible, to test pregnant women and shine a light on the womb to see if that would increase depth. If possible to try on cats before humans.
Also from reading the visual cliff study and shifting, is it possible if the redesign of the visual cliff increase which side an infant would prefer. On each side of the visual cliff deep and shallow there is the same pattern but a different depth. In infancy visual acuity is to fully developed, to its mature state. Having black and white blocks in a child vision would look as grey on each side showing no visual preference or stimulation for a side. Trying different visual cliff apparatus with different designs and colors, but introduce colored visual cliff when colored vision has matured in an infant. T.
S. Eliot stated that, 'What we call the beginning is often the end. And to make an end is to make a beginning. The end is where we start from." This quote explains the process of depth perception in humans. Even though with so much information from centuries, we still have to go back to the start to understand where we are heading with perception and where we want it to go. From a biological stand point we understand how it works with the Central Nervous System.
One problem is how the brain actually is fooled and when perception in infants and other animals are completely different. In conclusion, after understanding the dynamic system of vision with the concentration of perception and depth perception contained much research since 1980. Bibliography Adelson, E. , & Freiberg, S. , Gross Motor Development in Infants Blind from Birth, Child Development, 1974, (45) 114-126 Bennett, I.
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