The terms visual perceptual skills and visual processing skills are often used interchangeably, and refer to the skills that a person uses to make sense of what they see. Recognising letters and numbers, matching shapes, recognising a face, finding a toy in a messy cupboard, reading a road sign – these are all examples of how visual perception is used in everyday life.
A visual perceptual deficit refers to a reduced ability to make sense of information taken in through the eyes, and should be distinguished from the types of visual deficits that are most commonly associated with the blind and partially sighted, that is, deficits in visual acuity. The latter defects are caused by improper functioning of the sensory organ itself — the eye — due to malformation, injury, or disease. The visual perceptual problems addressed within the field of learning disabilities are concerned with problems that occur despite the fact that the child has structurally sound eyes and adequate muscular control over them.
To understand what a visual perceptual deficit is one must understand the meaning of the word perception. Perception is concerned with the interpretation of information through the five senses. In the act of reading visual perception plays a very important role. In order to read, a person must continually discriminate between foreground and background, forms, sizes and spatial relations. Of course, lack of experience may cause a person to misinterpret what he has seen. In other words, perception represents our apprehension of a present situation in terms of our past experiences, or, as stated by the philosopher Immanuel Kant (1724-1804): “We see things not as they are but as we are.”
The following situation illustrates how perception correlates with previous experience:
Suppose a person parks his car and walks away from it while continuing to look back at it. As he moves further and further away from his car, it will appear to him as if his car is gradually becoming smaller and smaller. However, in such a situation, none of us would gasp in horror and cry out, “My car is shrinking!”
Although the sensory image of the car is shrinking rapidly, we do not interpret that the car is changing size. Through past experiences we have learned that objects do not grow or shrink as we walk towards or away from them. We have learned that their actual size remains constant, despite the illusion. Even when one is five blocks away from one’s car and it seems no larger than one’s fingernail, one’s interpretation would be that it is still one’s car and that it hasn’t actually changed size. This learned perception is known as size constancy.
Pygmies, however, who used to live deep in the rain forests of tropical Africa, were not often exposed to wide vistas and distant horizons, and therefore did not have sufficient opportunities to learn size constancy. Colin Macmillan Turnbull, an anthropologist and author of The Forest People, wrote about one pygmy who, when removed from his usual environment, was convinced he was seeing a swarm of insects when he was actually looking at a herd of buffalo at a great distance. When driven toward the animals he was frightened to see the insects “grow” into buffalo and was sure witchcraft had been responsible.
A person needs to interpret sensory phenomena, and this can only be done on the basis of past experience of the same, similar or related phenomena. Perceptual ability, therefore, heavily depends upon the amount of perceptual practice and experience that the subject has already enjoyed.
Visual processing deficits
Difficulties with visual perception affect how visual information is interpreted or processed. The person may have a difficulty to discriminate in terms of foreground-background, forms, size, and position in space. He may be unable to synthesise and analyse, and he may have a problem with visual closure.
Visual processing problems can interfere with many areas of a child’s learning, particularly reading and maths. Below are a few examples of how a visual processing deficit can interfere with learning:
- Form discrimination: Whether it be the differentiation of the shape of a circle from a square, or the letter B from P, the ability to perceive the shapes of objects and pictures is an important skill for the developing child to acquire. There is hardly an academic activity that does not require the child to engage in form discrimination.
The most obvious classroom activity requiring the child to discriminate forms is that of reading. The learning of the letters of the alphabet, syllables, and words will undoubtedly be impeded if there is difficulty in perceiving the form of the letters, syllables, and words. That the discrimination of letters is a crucial skill in the early stages of reading is evidenced by an extensive literature review conducted by Chall. She concluded that the letter knowledge of young children is a better predictor of early reading ability than the various tests of intelligence and language ability.
- Size discrimination: Capital letters, being used at the start of a sentence, sometimes look exactly the same as their lowercase counterparts, and must therefore be discriminated mainly with regard to size. A person who is unable to interpret size may, for example, find it difficult to distinguish between a capital letter C and a lowercase c.
- Spatial relations: This refers to the position of objects in space. It also refers to the ability to accurately perceive objects in space with reference to other objects. A person with a spatial problem may find it difficult to distinguish letters like b, d, p, and q.
- Synthesis and analysis: Synthesis refers to the ability to perceive individual parts as a whole, while analysis refers to perceiving the whole in its individual parts. Synthesis plays an important role in reading, while analysis is of special importance in spelling.
- Visual closure: Difficulties in visual closure can be seen in such school activities as when the young child is asked to identify, or complete a drawing of, a human face. This difficulty can be so extreme that even a single missing facial feature (a nose, eye, mouth) could render the face unrecognisable by the child.