The visual sense

Vision is a primordial sense in humans

Vision is at the centre of our interactions with the outside world, it gives us the possibility to identify and recognise people and objects. It also allows us to act on them and to guide our various behaviours.

With the arrival of new imaging technologies, studies have shown that the central nervous system becomes functional from the third trimester of gestation. It still seems very immature, but during this trimester it gradually develops, and sensory and perceptive capacities are perfected. Furthermore, research shows that learning continues beyond the end of gestation, indicating a transnatal continuity of the functionality of the sensory, perceptual and memory systems.

For a long time, we thought that the newborn child could not see anything at birth. As many parents testify, newborns stare and look from the moment they come into the world. They move their eyes to explore and interact with their environment. Indeed, they are able to see but their vision is not yet fully mature.
At birth the baby’s vision is rather blurred, it is the least developed sense. During the first year, the baby’s visual functions improve rapidly under the effects of the combination of biological maturation and environmental stimuli. We are going to present various observations which show that the sight of the small child develops progressively and accompanies him throughout his motor, cognitive and social development. The child understands very quickly that sight is an essential sense for integrating new information about its environment. Vision is the foundation of our learning and our relationship with the world. We find it in the first glances exchanged but also in the first steps and the first words read.
The visual system is not only the eye, the organ necessary for vision, it is a much more complex system that extends from the cornea to the brain. The eye sees the scene and then prints it on the retina which transmits electrical signals to the occipital cortex.
It is these visual brain areas that allow us to detect, identify, localise, remember and recognise. This visual system develops from conception to about six years of age, both anatomically and functionally.

How to assess the visual abilities of infants : the preferential gaze

In 1958, Fantz used patterns such as triangles, crosses, and circles to show the evolution of the infant’s vision with age. The baby has a preferential and automatic interest in stimuli with a maximum of contrasts and storytelling, whereas smooth and uniform stimuli do not arouse any interest in the small child. Around 1962, the same author perfected his protocol, adding black and white stripes. This technique made it possible to measure the separating power of the eye. The observation work of Fantz & all. (1962) proved that infants prefer to look at one pattern rather than another exposed on a homogeneous surface. These early studies are the basis for contemporary methods of studying infant vision.

Later, Teller continued and deepened the method to develop a rigorous psychophysical protocol called forced-choice preferential looking. This method consists of observing the choice of the child’s gaze, does it go to the right or to the left depending on the stimulus presented on one side of a surface. This procedure allows Teller to explore the various visual abilities.

Summary of the development of the visual system in children
Development of the eye

The first stimulation of the eye is through light. When we see an object, light rays reflect off the object, enter the eye and make an impression on the retina. Our visual quality depends on many factors such as the quality of the lighting, the size of the object, the ability of our eyes to converge on the object and the depth of our eye, which determines how the light rays are projected onto the retina.

The size of our eye increases progressively from birth to adolescence, but it grows the most during the first year. The depth of the eyeball, cornea and retina measures :

  • 16 mm in newborns
  • 21 mm at one year
  • 25 mm in adolescents

As the eyeball increases, the quality of the perceived image improves.

The retina

The retina is located at the back of the eye, and in the centre is what is known as the fovea, which allows precise vision. It is in this fovea that visual acuity is best. At birth, the foveal part of the retina is still immature. From the first weeks of life, the number of cones in the fovea increases, their shape changes, they become longer and thinner, which allows a better capture of light waves and increases the perception of contrast and colours. The fovea develops rapidly during the first two months and reaches maturity around the age of four when visual acuity is at its maximum.

The peripheral retina is composed of rod cells. Vision is much less precise. However, it is the area of the peripheral retina that we can detect movement. This part of the retina reaches its fullness around fifteen months. This explains why babies are more easily attracted to moving targets.

The difference between the central retina (fovea) and the peripheral retina explains the ability of a baby of a few weeks to direct his gaze towards a visual stimulus that enters his peripheral visual field in order to see this stimulus better in foveal vision. This ability is very important, it gives us the possibility to orient our attention in space. It is essential to enter into a relationship with our external environment.

Acuity and visual field

Two parameters will gradually increase during the first months: visual acuity and visual field, but also adaptation to light and visual exploration will improve. At birth, the baby sees imprecise shapes, which is probably due to limited visual acuity. Very quickly, this visual acuity develops :

  • At three months, it reaches 1/10th
  • At six months, it is 2/10ths
  • At one year, it reaches 4/10ths

It is identical to that of an adult, i.e. 10/10ths at four/six years of age.

The visual field is defined as the area of space within which we can detect or locate visual information without moving our eyes. In adulthood, this visual field measures 180° laterally and 115° vertically. When babies are born, their visual field is very small, measuring about 20° vertically and 60° laterally. At birth, they see at a distance of 20 cm, which corresponds to the distance between their face and their mother’s face when she feeds her baby. When an object is moved slowly, children can follow it with their eyes. Furthermore, of all visual stimuli, the infant’s preference is for human faces. This attraction to faces is important for the early relationship between mother and child and for the child’s emotional, relational and cognitive development. The visual field expands very quickly, and its development stabilises at the end of the first year.

Visual system

Adaptation to light

As early as 28 weeks, brain imaging and changes in heart rate show that fetuses are reactive to light. Observation of fetuses has shown that their visual system is functioning. Fetuses alternate moments of visual fixations and moments of eye movements while living in semi-darkness. Eye movements in fetuses are not yet necessary, but they prepare the system to perceive the outside world at birth. During the last three months of gestation, their experience enables them to discern differences in light and to become familiar with moving elements. As a result, children are born, albeit limited, with visual experience.

Babies who have just come out of a dark environment are very sensitive to light, preferring places where the light is subdued. When the light is too strong, they systematically close their eyes. The pupil plays the same role as in adults, it decreases when the light is bright and increases in a dark environment so that the maximum number of light rays reach the retina.

Eye saccades

Eye movements allow us to detect, fix and follow objects in our environment. From birth, babies are able to alternate moments of fixation and eye movements in order to follow an object in their field of vision. However, they do not yet have full control over the amplitude of their saccades. The direction to the object is accurate but the baby’s eyes may miss the target. The newborn must make several corrective eye saccades. The saccades become accurate around four months.

Visual tracking

When a target is moving, our eyes move in the direction of the target and at the same speed. In visual tracking, we make slow, combined movements of both eyes. When we slowly show babies a contrasting target (black and white spiral), we see that they pursue the target. In the first few weeks, tracking is done by combining head movements and then as babies grow, they follow their target by moving only their eyes. Around four months, visual tracking becomes more fluid. It evolves and stabilises regardless of the target at around twelve months. From birth, a newborn can fix and follow a slowly moving target, but the object must be between 20 and 50 cm.

Development of the cortical visual system

As we have just seen, the eyes are the first stage of visual processing, but the information must be transmitted through the optic nerve and then through the visual pathways to the brain regions involved in vision, which will decode the information. The visual pathways are established by five-seven months but become mature by seven-eight years of age. The primary visual areas in the occipital cortex increase and mature by the age of eleven/twelve.

It is important to note that the maturation of the visual system, particularly the visual pathways and brain centres of vision, will develop primarily through visual experiences. The more numerous, varied and of good quality visual simulations will be during this period, the more harmoniously the child’s visual system will develop.

Summary of the development of visual perception

Development of the eye

The eye is an essential element, but it is only the first link in the chain of visual processing. Subsequently, the visual information captured by the eye is transferred to the brain regions specialised in vision where it is decoded.

From birth, all the senses of small children are awake and allow them to open up to the world. They observe their environment and thus begin to integrate a large number of elements related to their surroundings. All the interactions that we develop with children bring them information that goes to their brain. This information is stored, organised and interpreted. The new sensations discovered and learned form the basis for the development of perception. Perception is the interpretation of the world around us. However, a distinction must be made between sensations that are objective while perception is subjective.

The cortical areas of vision
Neuroscience research shows that from birth, babies are able to use highly complex visual processing. In the first few months, babies can easily distinguish contrasts. Gradually, they have the ability to fix an object and focus their two eyes on a point. As a result, they perceive movements and reliefs. Before 4 months, babies do not yet coordinate their eyes, they squint from time to time. Later, at around 4-7 months, they adjust their vision to different distances. Babies are immediately attracted to places where there are many things to see and observe in order to train their visual mechanisms. If we put small children in a white room with no scenery, the newborns will look around vaguely. As soon as we present them with objects or people, their gaze will immediately come to life.
It is important to distinguish between the visual system and perceptual abilities. Even though the infant’s visual system is still developing, its perceptual abilities are efficient.

Contrasts and colours

Newborns have a preference for high-contrast objects, such as black and white. But this does not mean that they see in black and white, they live in a rather colourful world. However, their colour spectrum is not identical to that of adults. They can distinguish between green, red, yellow and white. But they do not yet distinguish between colours. Moreover, the colour blue is absent because the cones corresponding to the detection of this colour are not yet operational. It is only at the age of two months that the baby has the same ability to distinguish colours as an adult.

As soon as they are born, babies are able to inaccurately distinguish the shapes of objects and people, as they are very sensitive to contrasts. Children often focus on dark objects on light walls because they are more visible to them. It is only when the fovea becomes mature that children’s visual acuity improves. So if you want to develop this acuity, you need to have children look at large, high-contrast objects. Furthermore, if the contrasting objects are of different shapes, children can distinguish between curvilinear and rectilinear shapes. They are more attracted to real objects than to objects in photographs, and they also have a preference for heterogeneous rather than homogeneous shapes, and horizontal rather than vertical lines. Furthermore, babies are very sensitive to biological movements, i.e. points of light that mimic human movements.

Perceptual constants

When we look at an object, the size of the object varies on our retina depending on the distance. However, no matter how far away we are from the object, we see that it is the same size. It is our brain that constantly corrects the retinal projection by taking into account the distance of the object. The baby’s brain is capable of perceptual constancy from birth. The child’s visual world is therefore stable.

Sight and the other senses

The development of the brain is stimulated by information from hearing, sight, taste, smell and body movements. Children’s development occurs not only with each sense but also when the different senses interact with each other. When children discover an object, they use touch, vision, hearing and smell.

At around 6 months, they associate hearing and vision by linking voice and face.

The association between touch and vision contributes to the discovery of the body. The first limb to be discovered is the hand, which is in their visual field. They see it, move it, open it, close it, can bring it to their mouth. They can control it.

Before being able to grasp an object, children can discover their characteristics through vision. They see and register whether the object is big or small, bright or dull, moving or still.

As vision develops, children assess distances to objects. They appreciate movements in their environment. They also develop a sense of depth.

To conclude

Seeing is a sense that goes beyond looking at and following people or objects. We must not forget that it also involves finding one’s bearings in space, directing one’s visual attention, choosing the visual information to be processed, and learning to recognise familiar faces and places. These different cognitive processes are not only processed in the visual areas but in all brain regions. Throughout our lives we acquire new knowledge through our visual experiences and interactions with the world.

The development of babies’s visual skills encourages them to look at objects, to stare at them and to follow them as they move. They register their features. In addition, they judge distances and depth. From the very beginning, they look at human faces and decode emotional messages. Through their eyes, they communicate their needs and desires.

Editor: Chantal Caracci Simon