Vision Development (0 - 6 Months) Print
Research Review / Parent
Written by: Sunita Shankar, Barbara-Ann Robertson, and William R. Bobier, University of Waterloo
Newborns possess rudimentary forms of most adult capacities. Even though full visual maturation may take several years, the first six months of a baby's life include rapid development and dramatic changes in vision. Changes include intricate changes within the eye, the brain, and the connections between the two. A baby's vision cannot develop until the brain is able to process visual information, and the brain cannot process visual information until the eye itself can pick up information from the baby's environment. A baby's vision capabilities improve rapidly over the first six months because the eye and brain learn to work together to process visual information from the environment.
Physiology of Vision Development
The physiology of visual development describes the biological changes that take place with the connections within and between a baby's eye and the brain. The eye takes in visual information from the environment, and then this information is mapped onto to particular areas in the brain for processing. This 'processing' will give information to the baby as to what the object is, how far away it is, and whether it is moving.
Much of what we know about the development of the visual system has come from animal research. From this work, we know that as the brain develops it is able to process more complex and detailed visual information. At birth most processing occurs in structures located deep in the centre of the brain, and is almost reflexive.
Later, more evolved superficial areas ('cortex') located close to the surface of the brain develop and participate in the processing of visual information. It is in the cortex where complex thought and decision-making processes occur, along with integration of sensory and motor information so that we can interact with our environment. It is this change in where the visual information is processed (from primitive deep brain structures to the more evolved superficial areas of the brain) that provides for the dramatic improvement in vision that is seen over the first 6 months of an infant's life.
The area of the brain that is specifically dedicated to processing visual information is called the "primary visual" cortex. To identify this area, cup the back of your baby's head with your hand; the area under your hand is mostly visual cortex. Connections, called visual pathways, run between the eye, structures deep in the brain and the visual cortex, and these pathways are present at birth.
Even though these connections are present at birth they are immature and unable to process much visual information. As the brain and eye develop, these pathways become more efficient and precise allowing the baby to process more visual information and see more. Cells which respond to images formed at the back of the eye undergo structural changes that allow better discrimination of edges of dark and light and colour.
Changes in the eye-brain connections allow more rapid and efficient transmission of information. More cells in the visual cortex respond to different features of the visual input. In order for brain development in the visual cortex to be normal, babies must be exposed to a normal visual environment.
A normal visual environment is one that provides lots of stimulation. For example, having a mobile over your baby's crib and having toys of simple shapes and colours available provides important features of varying light and dark and colour along with motion. These simple shapes, colours, and motions will be processed to greater extents by your baby with growth. However, it should be noted that normal development needs only normal visual exposure and it is actually possible to over-stimulate a newborn's sensitive visual system.
From Birth to 6 Months
During the first six months of life, infants experience lots of changes in their vision development. These include changes to the light-receiving elements and their interconnections within the eye itself. This is a complex developmental process that will continue until the baby is approximately 45 months of age.
As visual pathways continue to develop babies are able to investigate their environment with new capabilities. For example, by about three months of age, infants should be able to recognize their caregivers through more facial details instead of its external outline. These new capabilities allow for visual processing to become more complex and diverse, and will allow your baby to see more and more as they grow older.
Development of Sensory Functions of Vision
Three sensory functions of vision most evident during the 0-6 month period of visual development include acuity, colour, and binocular vision.
Visual Acuity in a Black and White Environment and Related Functions
Visual acuity measures the resolving power of the eye. If you have ever had your eyes tested by naming letters on an eye chart you have been tested for visual acuity. Since eye charts cannot be used until a child learns to read, other methods are used to examine visual status in babies. Babies have some rudimentary levels of visual acuity because they prefer looking at a chart with black and white stripes rather than a simple one that is just grey. As they get older babies can start to see thinner and thinner black and white stripes. Visual acuity in infants is quite poor, it is just a fraction of what they will have as adults, but it increases steadily over the first three months, and over the first few years of life.
Since the newborn's visual acuity is quite poor, you might be wondering what your baby can actually see. If you were to have your newborn view the clock tower on Parliament Hill in Ottawa, your newborn could determine the outline of the tower but not the details of the clock itself. The outline of the tower would appear fainter to your newborn than it would to you. During the first 6 months of life the outline of the tower would become more distinct and more details of the clock face would become apparent but still not to the same level you can see it.
The same is true for how your baby sees you. Newborns are thought to be able to discriminate face-like features from a scrambled picture as young at 4-5 weeks, but babies prefer to look at the outside features of the face rather than the centre of the face. This preference is so strong that in one study, when a mother's hairline was covered up with a scarf, her baby could no longer recognize her. However, by three months of age babies preferred to look at facial features such as the eyes and nose and were not 'tricked' by the scarf.
At birth colour discriminations are weak or absent. When tested in the laboratory babies begin to discriminate red colours from green during the first two months from birth. What is not known is if a baby's experience of colour is what it is for adults. All that is known is that they start to prefer some colours over plain grey, and are quickly able to differentiate colours. By three months they can discriminate blue from yellow. At this point, your baby can see a complete range of colours. While this may not affect the paint colours you select for your baby's nursery, they have the capacity to recognize that you are changing it from blue to yellow, or a colour in-between.
Binocular vision is the ability to see one image through both eyes. Each eye takes in information about the surrounding environment, then through a process called "fusion" the brain (visual cortex) puts the two images together so that we only see one of everything that is in front of us.
Because the visual pathways leading to the visual cortex are immature at birth (see 'at birth' section), newborns do not have this ability. As with many other visual functions binocular vision develops quickly and is found in babies by approximately 3 months of age. Binocular vision brings with it the ability to enhance judgments of object position (depth). By about 4 months of age a baby can tell if an object is near or far away from them. By 6 months a baby's depth perception is similar to levels seen in adults. Unlike visual acuity which develops in a slow and steady fashion over many years, binocular vision is initially absent and then appears and matures rapidly over a few months.
It is fascinating that six specialized eye muscles receive commands from three separate cranial nerves and hold the eyes steady while looking at an object in spite of head and body movements. In addition, this 'oculomotor system' can disengage fixating on an object to allow a rapid shift in gaze to fixate on a new object or start to track a moving one.
Gaze Stabilization and Fixation
Gaze stabilizing reflexes, which keep the eye steady while viewing an object, are present at birth. The degree to which a baby's eye can follow a moving object is limited by necessary maturation of components within the eye and brain. Therefore, while newborns can follow a moving object, they often cannot do so quickly enough. By approximately six months, infants are much better at tracking and in fact appear to do so as well as adults.
Ocular Alignment (Vergence) and Focus (Accommodation)
Being able to properly align the eyes and focus clearly are important motor aspects that accompany our binocular vision. This ability also develops significantly over the first 6 months of life.
When we are young and shift our eyes from viewing something far away to something close, a clear and flexible lens within our eye changes its focus through a process called accommodation. The alignment of the eyes must also adjust to the changing depth of the object, and this process is called mergence.
Newborns have some ability to change the alignment of their eyes, but it is very basic and limited; however, this ability becomes much more accurate over the first 3 months of life based on the maturation of their binocular vision capacity. Accommodation is also limited in newborns and similarly shows significant increases to adult-like ranges during the first 3 months of life.
Like eye alignment, this improvement relates more to their increased capacity to see objects more clearly which leads to a more active focusing response. However, accommodative accuracy is better when objects are close (75cm) vs. distant (150cm) until the infant reaches 6 months of age. Infants probably prefer closer objects because they have limited attention spans, and closer objects capture their attention.
Visual attention is the ability to concentrate on what is happening in our visual environment, and to change our attention when appropriate. This process is called 'cognitive' because it requires mature brain function to operate completely. However, certain aspects of visual attention develop early.
From birth to two months, babies develop what is called an 'alert state' where basically they become aware of what is happening around them.
From 2-3 months to about 6 months babies begin to understand where things are located in the environment around them and start to pay attention to specific objects.
From 5-6 months old, infants have the ability to self-direct visual attention. Instead of paying attention to the most obvious visual object in front of them, babies now have the ability to pay attention to what they want to. This important development in visual attention is due to the shift of processing from the deep brain structures to the cortical brain pathways. Also, disengagement of attention, which requires the infant to cancel attention from one object and shift it to another is also present in a rudimentary form very early in life, but appears to show considerable improvement from 2 to 4 months, again likely reflecting refined cortical development.
Summary: The Six Month Old Infant
Rapid changes occur in a baby's visual capacity in the first 6 months. The 6-month-old infant enjoys rudiments of all critical aspects of adult vision. They see colour, form and movement. Information is being gathered and processed binocularly. They are able to fixate and follow objects in their environment. They can recognize their caregivers, fixate on a novel stimulus, and supply sufficient focus to visually examine items within their grasp. These changes reflect growth in the visual function itself as well as improved visual attention. Motor development is close to adult levels where responses are limited by sensory development (such as visual acuity) and visual attention.
Shankar, S., Robertson, B-A., & Bobier, W.R. (2007). Parent/Caregive Narrative: Vision Development (0 - 6 Months). In L.M. Phillips (Ed.), Handbook of language and literacy development: A Roadmap from 0 - 60 Months. [online], pp. 1 - 5. London, ON: Canadian Language and Literacy Research Network. Available at: Handbook of language and literacy development