Perceptual Abilities in Babies free essay sample

We are able to see and interpret visual stimuli, and process this information in a way that is meaningful to us. We can also perceive the location of a sound, transform pressure changes in the air into meaningful sentences, and create myriad tastes and smells from our molecular environment. But are these perceptual abilities innate or learned? 19th century psychologists believed that newborns and young infants experience a confusing perceptual world, either perceiving nothing or making very little sense of the stimulation they are exposed to. However, research carried out over the last 30 years has changed the traditional view of the young infants perceptual world from one of incompetence to one of competence. This essay will discuss the capacities of newborn infants in terms of visual, auditory, olfactory and taste perception. One of the most basic questions we can ask about infant visual perception is how well infants can perceive details. Using the preferential looking technique and the visual evoked potential method, researchers have determined that the perception of details is poorly developed in infants at birth. Generally speaking, visual acuity for infants tends to be between 20/400 to 20/600 at one month. This increases rapidly over the first 6 to 9 months, with full adult acuity being reached some time after 1 year of age. The explanation for this is the result of a poorly developed visual cortex, and poorly developed cone receptors in the fovea. The shape of the cones in the fovea are vastly different from those of an adult, with newborns having comparatively fatter inner segments and smaller outer segments. The small outer segment cannot absorb light effectively, because they contain less pigment than that of adult cones. Additionally, the fat inner segment creates a coarse receptor lattice with large spaces between each cone. This means that most of the light entering the newborn fovea is lost in the spaces between the cones, and is therefore not useful for vision. Thus, newborns perceive the world as blurry and unclear relative to adults. Another important aspect of visual perception is the ability to distinguish an object from its background, also known as contrast sensitivity. This is measured by determining the smallest possible difference between dark and light bars of a grating at which an observer can still detect the bars. The number of cycles of a grating (in which one cycle is one light bar and one dark bar) per degree of visual angle is referred to as the spatial frequency of a grating. Adults tend to be most sensitive to spatial frequencies of about 3 cycles. However, infants ability to perceive contrast is restricted to low frequencies, and even at these low frequencies, the infants contrast sensitivity is much lower than the adults. Additionally, infants can see little to nothing at frequencies of about 2 to 3 cycles, the frequencies to which adults are most sensitive. At one month, infants can see no fine details and can only see relatively large objects with high contrast. Clearly, infants are sensitive to only a small fraction of the pattern information available to the adult. As well as fine details and contrast, an additional aspect of our visual world is the richness of colour. Adult perception of colour is determined by the action of three different types of cone receptors. Because these cones are poorly developed at birth, we can guess that a newborn would not have good colour vision. However, research has shown that colour vision develops early and appreciable colour vision is present within the first 3-4 months of life. Using the method of habituation, Bornstein et al. (1976) determined that 4-month old infants categorise colours the same way that adult trichromats do. Along with colour, contrast, and detail, another crucial aspect of vision is depth perception. In order to perceive depth, the eyes must be able to binocularly fixate, however, newborns only have a rudimentary ability to do this. Richard Aslin (1977) determined when binocular fixation develops by examining whether infants eyes diverge and converge when looking at an object moving away and closer respectively. He found that although some divergence and convergence do occur in 1- and 2- month old infants, these eye movements are not reliable until about 3-months. Another type of depth information is provided by pictorial cues. These develop later than disparity, presumably because they depend on experience with the environment and the development of cognitive capabilities. In general, infants begin to use pictorial cues such as overlap, familiar size, relative size, shading, linear perspective, and texture gradients somewhere between about 5 and 7 months old. Another important component of perception is the ability to hear. Although some early psychologists believed that newborns were functionally deaf, recent research has shown that newborns do have some auditory capacities and that this capacity improves as the child gets older. There is evidence to support the idea that infants can identify sounds they have heard before. DeCasper and Fifer found that babies regulated the pauses in their sucking so that they heard their mothers voice more than a strangers voice. They suggested that the newborns recognise their mothers voice because they heard their mother talking during development in the womb. Perceiving individual sounds is an important basic skill that infants posses, but as the infant develops, another skill becomes important- the ability to discern meaning through words and sentences. Infants begin the process of language acquisition by being able to detect very small differences between speech sounds. Initially, they can discriminate all possible speech contrasts (phonemes). Gradually, as they are exposed to their native language, their perception becomes language-specific, i. e. they learn how to ignore the differences within phonemic categories of the language. As infants learn how to sort incoming speech sounds into categories, ignoring irrelevant differences and reinforcing the contrastive ones, their perception becomes categorical. Infants learn to contrast different vowel phonemes of their native language by approximately 6 months of age. The native consonantal contrasts are acquired by 11 or 12 months of age. This is illustrated by the fact that a 4- month old Japanese infant can distinguish between the sounds /r/ and /l/, but by the time they are 1 year old, they can no longer make this distinction, as the Japanese language does not distinguish between these two sounds. There is evidence to support the notion that infants have the capacity to perceive odours and tastes. J. E. Steiner (1979) demonstrated that infants can smell and can distinguish between different olfactory stimuli. The infants responded to the scent of banana or vanilla essence with sucking and facial expressions resembling smiles, and they responded to concentrated shrimp odour and an odour resembling rotten eggs with a look resembling disgust. Similarly, research regarding the perception of taste has demonstrated that infants can distinguish sweet, sour and bitter tastes, but not salt (Beauchamp, Cowart Schmidt, 1991). Although responses to taste and olfaction do show some change as the infant grows into childhood, it could be argued that taste and olfaction are the most highly developed of all senses at birth. The elements of perception have been discussed separately, however, in the real world, these senses often occur together to form one combined sensory experience. The combination of senses is called intermodal perception. There is evidence to suggest that infants are capable of intermodal perception. This was demonstrated by Kuhl and Menstroff (1982), who found that infants could identify the sound that a person should be making based on how their lip movements looked. This ability has a number of important applications. For example, Sai (2005) suggested that because infants are already familiar with the mothers voice before they are born from listening to it in the womb, when they hear this familiar voice paired with the mothers face, this creates a link between the two and helps the infant recognise the mothers face.