Visual Perception Disability

Myra T. Merryll

University of Melbourne, Australia

Diagnostic features

A visual perception disability refers to a hindered ability to make sense of information taken in through the mind’s eye. There are a number of visual perception disabilities that are associated with how the brain is handling information that the eye sees. 

Visual discrimination

This is the ability to differentiate objects based on their individual characteristics. Visual discrimination is vital in the recognition of common objects and symbols. Attributes which persons use to identify different objects include: color, form, shape, pattern, size, and position. In terms of reading and mathematics, visual discrimination difficulties can interfere with the ability to accurately identify symbols, and gain information from pictures, charts, or graphs. One example in reading is being able to distinguish between “an/nl” and “Imp”, where the only distinguishing feature is the number of humps in the letters.

Visual closure

Visual closure is often considered to be a function of visual discrimination. This is the ability to identify or recognize a symbol or object when the entire object is not visible. 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 emerge even when there is a single missing facial feature (a nose, eye, mouth) and could render the face unrecognizable by the child. In reading, a student could have difficulty identifying incomplete words on the backboard. 

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. Reading and math are two subjects where accurate perception and understanding of spatial relationships are very important. Both of these subjects rely heavily on the use of symbols (letters, numbers, punctuation, math signs). Examples of how that difficulty may interfere with learning are in not being able to perceive words and numbers as separate units, and in directionality problems in reading and math, and confusion with similarly shaped letters, such as b/d/p/q. In math, one must be able to understand that certain digits go together to make a single number (i.e., 14), that others are single digit numbers, and that the operational signs (+, x, =) are distinct from the numbers, but demonstrate a relationship between them.

Object recognition (Visual Agnosia)

A number of children and adults are unable to visually recognize objects which are familiar to them, or even objects which they can recognize through their other senses, such as touch or smell. One school of thought about this difficulty is that it is based upon an inability to integrate or synthesize visual stimuli into a recognizable whole. Another school of thought attributes this difficulty to a visual memory problem, whereby the person cannot retrieve the mental representation of the object being viewed or make the connection between the mental representation and the object itself. Educationally, this can interfere with the child's ability to consistently recognize letters, numbers, symbols, words, or pictures.

Whole/part relationships

Some children have difficulty perceiving or integrating the relationship between an object or symbol in its entirety and the component parts which make it up. The common analogy is not being able to see the forest for the trees and conversely, being able to recognize a forest but not the individual trees which make it up. For example, “part perceivers” might be able to name the letters, or some of the letters within a word, but have great difficulty making up a whole, intact word. In creating artwork or looking at pictures, the “part perceivers” often pay great attention to details, but lack the ability to see the relationship between details. “Part perceivers could also be good at reading words and have an extensive vocabulary but their comprehension of stories and social situations lags far behind. “Whole perceivers”, on the other hand, might only be able to describe a piece of artwork in very general terms, or lack the ability to assimilate the pieces to have a deeper understanding.

Color Perception and Color Constancy

This involves the ability to distinguish different colors and to recognize different shades of color and light intensities. Because acquired color deficiencies are due to life events, they can be due to any number of different causes that affect the optic media – the eye, retina, visual pathways, or areas of the brain that process color information. “Acquired color vision deficiency” due to life events, can result from brain trauma, disease, or the effects of a toxic agent. Such acquired deficiencies are to be distinguished functionally from inborn or congenital deficiencies. Congenital deficiencies typically involve red-green confusion, whereas acquired deficiencies more often than not are a blue-yellow problem, called Kollner’s rule. Congenital deficiencies are linked to the X female chromosome, and are more prevalent in males than females. 

Visual Memory

Three types of memory are important to learning. “Working memory” refers to the ability to hold on to pieces of information (verbal or visual) until the pieces blend into a full thought or concept. For example, reading each word until the end of a sentence or paragraph and then understanding the full content. “Short-term memory” is the active process of storing and retaining information for a limited period of time. The information is temporarily available but not yet stored for long-term retention. “Long-term memory” refers to information that has been stored and that is available over a long period of time. Individuals might have difficulty with auditory memory or visual memory. These three types of memory are all involved in processing visual and/or verbal information.  Perceptual reasoning or reasoning without words requires information to be held in short-term memory, to be manipulated in working memory, and stored in long term memory. 

Diagnostic Criteria

Persons with a visual perception disability perform below the average range on subtests of visual perception skills. A visual processing disability is not diagnosed in persons with average cognitive abilities and average performance on academic tests. Most often, a visual-perception disability is associated with a learning disability. In fact, visual perception disabilities impact on different areas of learning, such as reading and writing, spelling, or math. For instance, visual-sequential processing difficulties are most often associated with math computations, and visual closure and spatial relations difficulties with reading comprehension. A number of tests such as the Test of Visual-Perceptual Skills (TVPS) (Morrison F. Gardner) assess different visual perceptual abilities: i.e., Visual Discrimination, Visual Memory, Visual Spatial Relationships, Visual Form-Constancy, Visual Sequential-Memory, Visual Figure-Ground, and Visual Closure.

Prevalence and Etiology

A visual processing or perceptual disability is among the most common causes of poor academic performance. About one out of four children have a visual processing disability that interferes with their ability to learn. Visual-perception disabilities often originate in the parietal lobe or the frontal lobe, which is involved in higher order processing. However, breakdowns along the neural pathways starting with the eye (input), to making sense of information (organization/integration), and storing and later retrieving information (memory) can interfere with visual-perception processing (output). As such, the specific visual-perception problems, much like auditory processing problems, result in learning disabilities in these four areas.

Interventions

Although learning disabilities often involve both visual perception and auditory perception difficulties, an effective intervention needs to aim at specific processing problems. Therefore, it is important to distinguish auditory memory (difficulty in remembering given verbal information or instructions) from visual memory (the ability to hold on to visual pieces of information) as it is to differentiate auditory discrimination or the ability to distinguish subtle differences in sound (called phonemes) from visual discrimination or the ability to differentiate objects based on their individual characteristics. Let us note that when multi-perception processing disabilities are involved, an effective intervention could require a multi-sensory approach or multimodal instruction.

A number of software programs are available to build visual perceptual skills; for instance, the Visual Perceptual Skills Builder CDs contain a comprehensive range of worksheets to stimulate the development of various aspects of visual perception and to encourage integration of visual perceptual skills in a child's schoolwork.

Books on visual perceptual skill building are also available; these help the student gain knowledge of the subject, and given strategies help the child develop critical thinking skills for reading, writing, and math; Visual Perceptual Skill Building, book 1, 2 and 3, by Raya Burstein. 

References

Burstein, Raya (2005). Visual Perceptual Skill Building (Book 1, 2 and 3). Puyallup: WA. Critical Thinking Co. 

Levine D. Melvin (2001). Developmental variation and learning disorders (2nd ed.). Cambridge, MA: Educators Publishing Service, Inc. (chap. 4: Spatial and temporal-sequential ordering, pp. 102-139).

Morrison, F. Gardner (1996). Test of Auditory Processing Skills (TAPS-3). Hydesville, CA: Psychological and Educational Publications, Inc.

National Center for Learning Disabilities (1999).  Visual and auditory processing disorders. LD online/article/6390. www.LDonline.org.

Visual Perceptual Skills Builder. London: England. Summerdale Educational Services Ltd. www.skillsforlearning.net.