Visual Perception

Anatomy of the Eye

A basic understanding of the anatomy and physiology of the eye aids comprehension of its influence on perception (Figure 12-1). The eye functions to transmit light to the retina, on which it focuses images of the environment. The eye is shaped to refract light rays such that the most sensitive part of the retina receives rays at a convergent point. The cornea covers the front of the eye and is part of the outermost layer of the eyeball. It plays a significant part in the focusing or bending of light rays that enter the eye. Behind the cornea is the aqueous humor, a clear fluid; the pressure of this fluid helps both to maintain the shape of the cornea and to focus light rays. The colored part of the eye, the iris, with its center hole, the pupil, is directly behind the cornea. The iris controls the amount of light entering the eye by increasing or decreasing the size of the pupil. The light then progresses through the crystalline lens, which does the fine focusing for near or far vision, and through a jelly-like substance called the vitreous humor.

The eye has three layers: the sclera, the choroid, and the retina. The sclera, which is fibrous and elastic, helps hold the rest of the eye structure in place; the choroid is composed primarily of blood vessels that nourish the eye; and the retina is the innermost layer. The retinal layer is composed of receptor nerve cells that contain a chemical activated by light. The retina has three types of receptor cells: cones, which are used for color perception and visual acuity; rods, which are used for night and peripheral vision; and pupillary cells, which control opening (dilation) and closing (constriction) of the pupil.

The fovea centralis, which is located in the retina, is the point of sharpest and clearest vision. It is most responsive to daylight and must receive a certain amount of light before it transmits the signal to the optic nerve. The retina responds to spatial differences in the intensity of light stimulation, especially at contrasting border areas, and provides basic information about light and dark areas. Light stimulates the visual receptor cells in the retina, causing electrochemical changes that trigger an electrical impulse to flow to the optic nerve. The optic nerve (cranial nerve II) transmits the visual sensory messages to the brain for processing. This information travels to the brain in a special way. Fibers from the nasal half of each retina divide, and half of the fibers cross to the contralateral side of the brain. Fibers from the outer half of each retina do not divide; therefore, they carry visual information ipsilaterally. Thus visual information from either the left or right visual field enters the opposite portion of each retina and then travels to the same hemisphere of the brain. This organization means that even with the loss of vision in one eye, information is transmitted to both hemispheres of the brain. It also means that damage in the region of the left or right occipital cortex can cause a loss of vision, referred to as a field cut, in the opposite visual field.⁷²

The optic nerve leads from the back of the eye to the lateral geniculate nucleus in the optic thalamus. It is here that binocular information is received and integrated at a basic level, which may contribute to crude depth perception. Information then passes from the two lateral geniculate bodies of the thalamus to the visual cortex in the occipital lobe (area 17). From the occipital cortex the refined visual information is sent in two directions via visual area 18 or 19.^109,110 Some impulses flow upward to the posterior parietal lobe, where visual-spatial processing occurs, focusing on the location of objects and their relationships to objects in space. This pathway is referred to as the dorsal stream. The magnocellular channel is dominant in the dorsal stream; this channel is associated with motion and depth detection, stereoscopic vision, and interpretation of spatial organization.⁶⁹ Other impulses flow downward to the inferior temporal lobe, where visual object processing takes place. Information sent here is analyzed for the specific details of color, form, and size needed for accurate object identification; the focus is on pattern recognition and detail and on remembrance of the qualities of objects. This is referred to as the ventral stream. The parvocellular channel is dominant in the ventral stream; this channel is thought to be important for color perception and for detailed analysis of the shape and surface properties of objects.⁸²

Visual-Receptive Functions

The oculomotor system enables the reception of visual stimuli (visual-receptive process). The visual-receptive components include visual fixation, pursuit and saccadic eye movements, acuity, accommodation, binocular fusion and stereopsis, and convergence and divergence. Visual fixation on a stationary object is a prerequisite skill for other oculomotor responses, such as shifting the gaze between objects (scanning) or tracking. Each eye is moved by the coordinated actions of the six extraocular muscles. These are innervated by cranial nerves III, IV, and VI (oculomotor, trochlear, and abducens nerves). The oculomotor nuclei are responsible for automatic conjugate eye movements (lateral, vertical, and convergence). They also help regulate the position of the eyes in relation to the position of the head. The nuclei receive most of their information from the superior colliculus.

Two types of eye movements are used to gather information from the environment: pursuit eye movements, or tracking, and saccadic eye movements, or scanning. Visual pursuit, or tracking, involves continued fixation on a moving object so that the image is maintained continuously on the fovea. The smooth pursuit system is characterized by slow, smooth movements. Tracking may occur with the eyes and head moving together or with the eyes moving independently of the head. Saccadic eye movements, or scanning, are defined as a rapid change of fixation from one point in the visual field to another. A saccade may be voluntary, as when localizing a quickly displaced stimulus or when reading, or it may be involuntary, as during the fast phases of vestibular nystagmus. A saccadic movement is precise, although the presence of a slight overshoot or undershoot is normal.

In addition to voluntary control of eye movements, the vestibulo-ocular pathways control conjugate eye movements reflexively in response to head movement and position in space. These pathways enable the eyes to remain fixed on a stationary object while the head and body move.

In addition to the tasks of visual fixation, pursuit movements, and saccadic movements, other visual-receptive components include the following:

For a more detailed description of the function of these components, see the textbook by Gentile.⁵⁷

Visual-Cognitive Functions

Interpretation of the visual stimulus is a mental process involving cognition, which gives meaning to the visual stimulus (visual-cognitive process). The visual-cognitive components are visual attention, visual memory, visual discrimination, and visual imagery.

Motor and Process Skills

Client factors may affect performance skills that in turn may affect activities and occupations. Motor skills of posture, mobility, and coordination may be affected by poor visual skills. For example, in the area of mobility, research has shown the importance of vision in the development of proprioception of the hand prior to the onset of reaching in newborn infants.³³ This can explain why young babies spend much time visually examining their hands. By 5 to 7 months, infants, in preparation for reaching, may use the current sight of the object’s orientation, or the memory of it, to orient the hand for grasping; sight of the hand has no effect on hand orientation at this point.⁹⁶ If problems occur in visual memory affecting the memory of the hand, the hand may not be properly oriented during reach, and this affects coordination.

Process skills of knowledge, temporal organization, organization of space and objects, and adaptation all can be affected by visual perception. Children who have acquired damage to the white matter around the lateral ventricles or damage to the posterior parietal lobes can find it difficult to use vision to guide their body movements.⁴⁷ For example, a floor boundary between carpet and linoleum can be difficult to cross because it looks the same as a step. Black-and-white tiled floors can be frightening to walk across. At a curb, the foot may be lifted to the wrong height, too early, or too late, and walking down stairs without a banister is difficult and dangerous.

Developmental Framework for Intervention

Warren presented a developmental framework based on a bottom-up approach to evaluation and treatment.¹⁵⁷ Using the work of Moore,⁶² Warren suggested that with knowledge of where the deficit is located in the visual system, the therapist could design appropriate evaluation and treatment strategies to remediate basic problems and improve perceptual function.¹⁵⁷ To apply this approach, the occupational therapist must have an understanding of the visual system, including both the visual-receptive and visual-cognitive components. Although Warren’s model was presented as a developmental framework for evaluation and treatment of visual-perceptual dysfunction in adults with acquired brain injuries, it is useful as a model for children with visual-perceptual deficits. A hierarchy of visual-perceptual skill development in the central nervous system is presented in Figure 12-2. The definitions of components of each level are provided in the following list and are used in later descriptions of intervention.

Warren’s model provides a framework for assessing vision alone, without consideration of the other sensory systems. When visual-perceptual problems relate to sensory integration (SI) dysfunction, models based on SI theories can guide evaluation and intervention.²⁰ These models consider organization of multisensory systems and the influence of vision as it integrates with other sensory systems.

Vision can be viewed as a dynamic blending of sensory information in which new visual and motor input are combined with previously stored data and then used to guide a reaction. Research demonstrates an expansive interconnectivity of sensory systems.¹⁴³ Studies of brain activity confirm that when an individual is using the visual system, many areas of the brain are activated. Evidence of full brain activity during visualization supports the concept that vision should be viewed in the totality of all sensory systems.

Visual-Receptive Functions

As with other areas of development, the development of visual-receptive process and abilities takes place according to a prescribed timetable, which begins in the womb. By gestational week 24, gross anatomic structures are in place, and the visual pathway is complete. Between gestational weeks 24 and 40, the visual system, particularly the retina and visual cortex, undergoes extensive maturation, differentiation, and remodeling.⁶² As early as the fifth gestational month, eye movements are produced by vestibular influences.⁴³ At birth the infant has rudimentary visual fixation ability and brief reflexive tracking ability. The visual system at this age is relatively immature compared with other sensory systems, and considerable development occurs over the next 6 months.⁶²

Toward the end of the second month, accommodation, convergence, and oculomotor subsystems are established.¹⁵ Stereopsis is evident at about 2 months of age; it does not appear to depend on visual recognition and does not need to be taught.¹⁶⁰ Maximum accommodation is reached at 5 years of age, and the child should be able to sustain this skill effort for protracted periods at a fixed distance.

Controlled tracking skills progress in a developmental pattern from horizontal eye movements to eye movements in vertical, diagonal, and circular directions. By kindergarten a child should be able to move the eyes with smooth control and coordination in all directions. This can be demonstrated by asking the child to follow with the eyes a moving object located 8 to 12 inches from the child’s face. If the child moves the head as a unit along with the eyes, this skill is still developing. Visual acuity is best at 18 years of age and tends to decline thereafter.

Visual-Cognitive Functions

Vision enables infants to acquire information from multiple locations at a range of distances and is a means for infants to organize information received from their other senses.¹⁴² By coordinating visual and auditory input, infants accumulate information as they explore places, events, and individuals in the physical and social environments.¹³⁷ Some visual-cognitive capacities are present at birth, whereas other higher-level visual-cognitive abilities are not fully developed until adolescence. This development occurs through perceptual learning, the process of extracting information from the environment. Perceptual learning increases with experience and practice and through stimulation from the environment.

Role of Vision in Social Development

The importance of vision in facilitating infants’ participation in social interactions has been widely recognized.⁹⁹ Facial expressions are an important way to communicate emotions.⁷⁶ Infants respond to attentive, social initiations from their parents by visually focusing on their parents’ eyes, smiling, and occasionally shifting gaze to scan their parents’ faces and the environment. Mutual gaze between parents and infants facilitates emotional attachment. Adults’ facial expressions appear to be the major driving force during social interactions with infants younger than 6 months. Infants discriminate between happy and sad facial expressions by 3 months of age. Toward the end of the first year an infant can shift attention from one person to another person, or to an object of mutual interest in joint attention paradigms.⁴² Social imitation then shifts from simple reactions to another person’s facial expressions to imitations of another person’s actions with objects. Toddlers will imitate a peer’s action on an object, but only when identical objects are available.

Visual-Receptive Functions

The importance of good vision for classroom work cannot be overemphasized. More than 50% of a student’s time is spent working at near-point visual tasks such as reading and writing. Another 20% is spent on tasks that require the student to shift focus from distance to near and near to distance, such as copying from the board. For more than 70% of the day, therefore, tremendous stress is put on the visual system.¹¹⁵ Many students with visual dysfunction may have difficulty meeting the behavioral demands of sitting still, sustaining attention, and completing their work. Academic instruction in the first years places great demand on the child’s visual processing skills, with emphasis on recognition, matching, and recall. In early elementary grades, periods of sustained near work are infrequent, and visual stimuli (letters) are relatively large and widely spaced.

Visual efficiency becomes a more significant need in later elementary grades, middle school, and high school. Letters and text become smaller and more closely spaced and reading requires more comprehension effort for extended periods of time. Students visually attend for sustained periods of near work.¹⁰²

Learning-related vision problems represent deficits in two broad visual system components: visual efficiency and visual information processing.¹³ Figure 12-3 presents a sample list of behaviors noted in children with specific visual problems.¹⁰² In addition, individuals with functional vision problems may exhibit⁵⁶:

Impairment of oculomotor control can occur through disruption of cranial nerve function or disruption of central neural control. The pattern of oculomotor dysfunction depends on the areas of the brain that have been injured and the nature of the injury.⁸⁸ Oculomotor problems can limit the ability to control and direct gaze. In addition, when large amounts of energy must be used on the motor components of vision, little energy may be left for visual-cognitive processing.⁷² Warren¹⁵⁷ and Scheiman¹²⁵ present detailed descriptions of oculomotor deficits and other deficits seen in visual-receptive components.

At least 20% of students with learning disabilities have been found to have prominent visual information–processing problems. The prevalence of visual efficiency problems in children with learning disabilities is thought to be in the 15% to 20% range.¹²⁶ Accommodative disorders have been reported in 60% to 80% of individuals with visual efficiency problems; accommodative insufficiency is the most prevalent type.¹⁰² Convergence insufficiency is the most common convergence anomaly.

Visual-Cognitive Functions

Diagnoses with Problems in Visual Perception

When children with disabling conditions have visual problems, the effects of the visual impairments can be tremendous. Numerous studies have found a high frequency of vision problems among individuals with disabilities.³² Severe refractive errors are common among children with developmental problems,¹¹⁷ and impaired visual attention can have a pervasive negative influence on the functional behavior of these children. Often considered distractible, these children may be able to locate objects but have difficulty sustaining eye contact or recognizing objects visually.¹¹⁷

Retinopathy of prematurity (ROP) is the single most cited cause of blindness in preterm infants. However, the number of infants with ROP has declined in past 25 years because of changes in medical interventions for premature infants.¹³⁶ Cortical visual impairment also occurs in preterm infants and is generally associated with severe CNS damage, such as periventricular leukomalacia. Other visual disorders common in preterm children include lenses that are too thick, poor visual acuity, astigmatism, extreme myopia, strabismus, amblyopia, and anisometropia (unequal refraction of the eyes).⁵ These children also have difficulty processing visual information. Scores for visual attention, pattern discrimination, visual recognition, memory, and visual-motor integration are lower than those for full-term infants.^29,120,132 Studies of older children suggest that these problems often persist.¹¹⁷

Children with developmental disabilities commonly have a coexisting diagnosis of blindness or other visual impairment. These children also may have sensory integrative deficits that further complicate their functional abilities.¹¹⁹

Children with cerebral palsy (CP) frequently have been identified as a group with visual-perceptual deficits.^17,21 Children with CP often have a strabismus, oculomotor problems, convergence insufficiencies, or nystagmus. These problems may also limit the ability to control and direct visual gaze.¹¹⁷

Early research indicated that the degree of perceptual impairment in individuals with CP was related to the type and severity of the motor impairment.¹⁰ In a comparison study, children with CP scored significantly lower on a motor-free test of visual perception than typical children.⁹⁶ These findings supported earlier studies that showed that a group of children with spastic quadriplegia demonstrated the greatest problems in visual perception. Children with left hemiplegia scored significantly lower than control children on motor-free visual tests, but children with right hemiplegia did not.²¹

In children with language delay, poorly developed visual perception may contribute to the language difficulties. For example, language moves from the general to the specific. Young children call every animal with four legs a dog. Eventually they are able to discriminate visually between dogs and lions, and the vocabulary follows the visual-perceptual lead. Next, they can tell Dalmatians from Dachshunds, but they are unable to recognize that both are dogs. Finally, the ability to categorize and generalize emerges somewhere between 7 and 9 years of age. In addition, the child who has visual-spatial perception deficits may show difficulty understanding directional language, such as in, on, under, and next to.

Visual-perceptual problems are found more frequently in individuals who have significantly higher verbal scores than performance scores on intelligence testing. Not all children with learning disabilities have visual-perceptual problems.⁷⁰ A recent study suggests that early brain damage can give rise to specific visual-perceptual deficits, independent of, although occurring in association with, selective impairment in nonverbal intelligence.¹³⁸

Children with learning disabilities may have difficulty filtering out irrelevant environmental stimuli and therefore have erratic visual attention skills. Children who have difficulty interpreting and using visual information effectively are described as having visual-perceptual problems because they have not acquired adequate visual-perceptual skills despite having normal vision.¹⁴⁴ Children with developmental coordination disorder (DCD) obtained significantly lower scores compared with typically developing children on a motor-free test of visual perception.¹⁴⁷ Although group differences were statistically significant, some of the children with DCD did not have general visual-perceptual dysfunction.

Dyslexia is best understood as a neurocognitive deficit that is specifically related to reading and spelling processes. Dyslexia can occur for two different reasons. One cause is that the reader has difficulty decoding words (single word identification) and encoding words (spelling).¹³² A second reason for dyslexia is that the reader makes a significant number of letter reversals (b – d), letter transpositions in words when reading or writing (sign – sing) or has right-left confusion.⁶⁶

Daniels and Ryley studied the incidence of visual-perceptual and visual-motor deficits in children with psychiatric disorders.³⁹ In their study, deficits in visual-motor skills occurred far more frequently than deficits in visual-perceptual skills. When visual-perceptual problems occurred, they did so in conjunction with visual-motor skill problems.

Some children with autism have demonstrated poor oculomotor function.¹²¹ Children with autism often do not appear to focus their vision directly on what they are doing.¹⁰³ A possible explanation is that they use peripheral vision to the exclusion of focal vision. One study found that children with autism spend the same amount of time inspecting socially oriented pictures, have the same total number of fixations, and have scan path lengths similar to those of typically developing children.¹⁵³ These results do not support the generally held notion that children with autism have a specific problem in processing socially loaded visual stimuli. The study authors suggested that the often-reported abnormal use of gaze in everyday life is not related to the nature of the visual stimuli, but that other factors, such as social interaction, may play a role.

Effects of Visual-Perceptual Problems on Performance Skills and Occupations

The effects of visual-perceptual problems may be subtle. However, when the child is asked to perform a visual-perceptual task, he or she may be slow or unable to perform it. Because visual-perceptual dysfunction affects the child’s ability to use tools and to relate materials to one another,⁴ bilateral manipulative skills are affected to a greater degree than the child’s basic prehension patterns indicate. The child with visual-perceptual deficits may show problems with cutting, coloring, constructing with blocks or other construction toys, doing puzzles, using fasteners, and tying shoes. Visual perception deficits also can influence children’s areas of occupation, such as activities of daily living (ADLs), education, work, play, leisure, and social participation.

Children with visual-perceptual problems may demonstrate difficulty with ADLs. In grooming, the child may have difficulty obtaining the necessary supplies and using a brush and comb and mirror to comb and style the hair. Applying toothpaste to the toothbrush may be difficult for the child. Using fasteners; donning and doffing clothing, prostheses, and orthoses; tying shoes; and matching clothes may present problems. Skilled use of handwriting, telephones, computers, and communication devices may present difficulty for the child with visual-cognitive problems. Instrumental ADLs, such as home management, may present problems. For example, the child may have trouble sorting and folding clothes. Community mobility may be difficult because the child is unable to locate objects and find his or her way. In play, the child may demonstrate difficulty with playing games and sports, drawing and coloring, cutting with scissors, pasting, constructing, and doing puzzles.

Classroom assignments may present problems for the child with visual-perceptual problems. He or she may have difficulty with educational activities such as reading, spelling, handwriting, and math. The educational problems seen in the school-aged child are considered in some detail next. Visual processing deficits are considered developmental. With maturation and experience the performance of the child with deficits improves, but the rate of maturation of skill continues to lag.

Evaluation of Visual-Receptive Functions

Evaluation should begin by focusing on the integrity of the visual-receptive processes, including visual fields, visual acuity, and oculomotor control.¹⁵⁸ In children who have deficits in these foundational skills, insufficient or inaccurate information about the location and features of objects is sent to the CNS, and the quality of their learning through the visual sense is severely affected. Warren suggested that what sometimes appear to be visual-cognitive deficits are actually visual-receptive problems, which may include oculomotor disturbances.¹⁵⁶ Therefore, visual-receptive and visual-cognitive deficits may be misdiagnosed. The occupational therapist should be familiar with visual screening, because evaluation of vision and oculomotor skills assists in the assessment and analysis of their influence on visual perception and functional performance.¹⁴⁴

Visual screening consists of basic tests administered to determine which children are at risk for inadequate visual functions.^15,72 The purpose of the screening is to determine which children should be referred for a complete diagnostic visual evaluation. Therefore, the purpose of screening the visual-receptive system is to determine how efficient the eyes are in acquiring visual information for further visual-cognitive interpretation. The checklist presented in Figure 12-3 can alert the therapist to visual symptoms commonly found in children who demonstrate poor visual performance.

Perimetry (computerized measurement of visual field by systematically showing lights of differing brightness and size in the peripheral visual field), confrontation, and careful observation of the child as he or she performs daily activities provide useful information about field integrity.¹⁶⁵ For example, missing or misreading the beginning or end of words or numbers may indicate a central field deficit.

The child’s refractive status, which is the clinical measurement of the eye, should be determined. A school nurse or vision specialist usually performs this test. The refractive status reflects whether the student is nearsighted (myopic), farsighted (hyperopic), or has astigmatism. Several methods can be used to determine a child’s refractive status. One method, the Snellen test, is used to screen children at school or in the physician’s office. However, it measures only eyesight (visual acuity) at 20 feet. This figure, expressed commonly as 20/20 for normal vision, has little predictive value for how well a child uses his or her vision. It is estimated that the Snellen Test detects fewer than 5% of visual problems.¹²⁹ When a child passes this screening, he or she may be told that the existing vision is fine. However, it is only the eyesight at 20 feet that is fine.

Some schools and clinics use a Telebinocular or similar instrument in vision screening. This device provides information on clarity or visual acuity at both near and far distances, as well as information on depth perception and binocularity (two-eyed coordination). Warren suggested that the Contrast Sensitivity Test is best for measuring acuity.¹⁵⁸ A pediatric version of this test is available (Vistech Consultants, Dayton, Ohio).

The occupational therapist may observe oculomotor dysfunction in the child. The screening test should answer several questions, including the following^73,165:

In addition, the child’s ocular health should be evaluated. The presence of a disease or other pathologic condition, such as glaucoma, cataracts, or deterioration of the nerves or any part of the eye, must be ruled out. An interview with the family regarding significant visual history helps identify any conditions that may be associated with visual limitations. This information can also be obtained from a review of the child’s records and from consultation with other professionals involved in direct care of the child (e.g., teacher or physician).

When visual problems are detected in screening, the child may be referred to a vision specialist such as an optometrist. The specialist can help determine whether the child has a visual problem that might be causing or contributing to school difficulties. The therapist then will be able to understand the effect those deficits have on function and can devise intervention strategies by designing and selecting appropriate activities that are within the child’s visual capacity.¹⁵

Evaluation of Visual-Cognitive Functions

Clinical evaluation and observation may be the occupational therapist’s most useful assessment methods. The therapist should observe the child for difficulty selecting, storing, retrieving, or classifying visual information. Observations may include visual search strategies used during visual-perceptual tasks (e.g., outside borders to inside), how the child approaches the task, how the child processes and interprets visual information, the child’s flexibility in analyzing visual information, methods used for storage and retrieval of visual information, the amount of stress associated with visual activities, and whether the child fatigues easily during visual tasks. The therapist should analyze the tasks observed carefully to determine what visual skills are needed and to identify the areas in which the child has difficulty.

Tsurumi and Todd have applied task analysis to the nonmotor tests of visual perception.¹⁵⁰ This information greatly assists the therapist in analyzing the results of these tests. Currently, the best method for evaluating visual attention in children is informal observation during occupational performance tasks. Standardized assessments that may be used include the following:

Visual-Spatial Tests

Visual-Perceptual Tests

Visual-Motor Integration Tests

These tests can be used to evaluate how the child is processing, organizing, and using visual-cognitive information. Care should be taken in interpreting and reporting test results because it is not always clear what visual-perceptual tests are measuring. Because of the complexity of the tests, it is certain that they tap different kinds and levels of function, including language abilities.

The effectiveness of any treatment method is largely determined by how the child is diagnosed; therefore, careful analysis of test results and observations is important. Burtner et al. provided a critical review of seven norm-referenced, standardized tests of visual-perceptual skills frequently administered by pediatric therapists.²² Each assessment tool was critically appraised for its purpose, clinical utility, test construction, standardization reliability, and validity. Discussion focused on the usefulness of these assessment tools for describing, evaluating, and predicting visual-perceptual functioning in children.

Theoretical Approaches

The theoretical approaches that guide evaluation and treatment of visual-perceptual skills can be categorized as developmental, neurophysiologic, or compensatory. The developmental model devised by Warren,^157,158 described in a previous section, is based on the concept that higher level skills evolve from integration of lower level skills and are subsequently affected by disruption of lower level skills. Skill levels in the hierarchy function as a single entity and provide a unified structure for visual perception. As pictured in Figure 12-2, oculomotor control, visual field, and acuity form the foundational skills, followed by visual attention, scanning, pattern recognition or detection, memory, and visual cognition. Identification and remediation of deficits in lower level skills permit integration of higher-level skills. Occupational therapists who follow this model need to evaluate lower level skills before proceeding to higher level skills to determine where the deficit is in the visual hierarchy and to design appropriate evaluation and intervention strategies.

The neurophysiologic approaches address the maturation of the human nervous system and the link to human performance. These approaches help create environmental accommodations to sensory hypersensitivity and visual distractibility. They also promote organization of movement around a goal, reinforcing the sensory feedback from that movement. Neurophysiologic approaches emphasize the importance of postural stability for oculomotor efficiency. The role of visual perception as part of sensory integration and the way the child perceives his or her environment are discussed in Chapter 11. The neurophysiologic approaches focus on improving visual-receptive and visual-cognitive components to enhance a child’s occupational performance.

Learning theories and behavioral approaches emphasize a child’s development of visual analysis skills. The therapist provides the child with a systematic method for identifying the pertinent, concrete features of spatially organized patterns, thereby enabling the child to recognize how new information relates to previously acquired knowledge on the basis of similar and different attributes. Because the child learns to generalize to dissimilar tasks, that improvement in visual-perceptual skills leads to increased levels of occupational performance.

In compensatory approaches, classroom materials or instructional methods are modified to accommodate the child’s limitations. The environment can also be altered or adapted. The therapist may work with the classroom teacher on behalf of the child to provide necessary supports. Adaptation and compensation techniques can include reducing classroom visual distractions, providing visual stimuli to direct attention and guide response, and modifying the input and output of computer programs. In daily living skills, adaptations to increase grooming, dressing, eating, and communication skills can be made. In play situations, toys can be made more accessible, and in work activities, adaptations can be made to promote copying, writing, and organizational skills. Box 12-1 outlines compensatory instruction guidelines.

Perceptual training programs use learning theories to remediate deficits or prerequisite skills and have been implemented in the public schools for more than 2 decades. Occupational therapists generally use activities from these approaches in combination with neurophysiologic and compensatory approaches.

Optometry and occupational therapy have common goals related to the effects of vision on performance.^72,125 When a visual dysfunction is identified, sometimes only environmental modifications (e.g., changes in lighting, desk height, or surface tilt) are needed to alleviate the problem. In many cases, glasses (lens therapy) are prescribed to reduce the stress of close work or to correct refractive errors. In other cases, optometric vision therapy may be prescribed by an optometrist and carried out collaboratively with an occupational therapist. Through vision therapy, optometrists provide structured visual experiences to enhance basic skills and perception. Vision training is well supported by evidence but should be performed only under supervision of an optometrist. Collaboration between the occupational therapist and the optometrist is supported by case studies and clinical judgment.

Intervention Strategies

For a child of any age, an important treatment strategy is education regarding the problem the child is experiencing.¹⁵⁰ The occupational therapist can help interpret the functional implications of the vision problem for the child and his or her parents, caregivers, and teachers. At times this can be the most helpful intervention for the child. This section presents intervention suggestions according to age groups. However, activities should be analyzed and then selected according to the child’s needs rather than according to his or her age group.

These activities illustrate both the developmental and compensatory approaches. Often activities combine approaches. For example, when classroom materials are adapted so that the print is larger and less visual information is presented (compensatory approach), the child might be better able to use visual-perceptual skills, with resulting improvement in those skills (developmental approach). For each age group, the focus of intervention is occupation in natural environments. The aim of occupational therapy intervention is to reduce activity limitations and enhance participation in everyday activities.¹⁴⁵

1. Adams, W., Sheslow, D. Wide range assessment of visual motor abilities manual. Wilmington, DE: Wide Range, Inc, 1995.

2. American Occupational Therapy Association (AOTA), Occupational therapy practice framework: Domain and process, 2nd ed. American Journal of Occupational Therapy, 2008;62:625–683.

3. Arguin, M., Cavanagh, P., Joanette, Y. Visual feature integration with an attention deficit. Brain and Cognition. 1994;24:44–56.

4. Ayres, A.J. Sensory Integration and the Child. Los Angeles: Western Psychological Services, 1979.

5. Batshaw, M.L., Pellegrino, L., Roizen, N. Children with handicaps: A medical primer, 6th ed. Baltimore: Brookes, 2007.

6. Beery, K.E., Beery, N.A. Developmental Test of Visual-Motor Integration with supplemental Developmental Tests of Visual Perception and Motor Coordination: Administration, Scoring, and Teaching Manual, 5th ed. Upper Saddle River, NJ: Pearson, 2004.

7. Bell, N. Visualizing and verbalizing for language comprehension and thinking. Paso Robles, CA: Academy of Reading Publishers, 1991.

8. Bell, B., Swinth, Y. Defining the role of occupational therapy to support literacy development. School System Special Interest Section Quarterly. 2005;12(3):1–4.

9. Benbow, M. Loops and other groups. Tucson, AZ: Therapy Skill Builders, 1990.

10. Birch, H.G. Brain damage in children: The biological and social aspects. New York: Williams & Wilkins, 1964.

11. Blanksby, B.S. Visual therapy: A theoretically based intervention program. Journal of Visual Impairment and Blindness. 1992;86:291–294.

12. Blaskey, P., Scheimen, M., Parisi, M., Ciner, E.B., Gallaway, M., Sleznick, R. The effectiveness of Irlen filters for improving reading performance: A pilot study. Journal of Learning Disabilities. 1990;23:604–612.

13. Borsting, E. Visual perception and reading. In: Garzia R., ed. Vision and reading. St. Louis: Mosby, 1996.

14. Bouldoukian, J., Wilkins, A.J., Evans, B.J.W. Randomised controlled trial of the effect of couloured overlays on the rate of reading of people with specific learning difficulties. Ophthalmic & Physiological Optics. 2002;22:55–60.

15. Bouska, M.J., Kauffman, N.A., Marcus, S.E. Disorders of the visual perception system. In Umphred D.A., Lazaro R.T., eds.: Neurological rehabilitation, 6th ed., St. Louis: Elsevier, 2006.

16. Bowers, P.G., Ishaik, G. RAN’s contributions to understanding reading disabilities. In: Swanson H.L., Harris K.R., Graham S., eds. Handbook of learning disabilities. New York: Guilford Press; 2003:140–157.

17. Breakey, A.S., Wilson, J.J., Wilson, B.C. Sensory and perceptual functions in the cerebral palsied. Journal of Nervous and Mental Diseases. 1994;158:70–77.

18. Deleted in proofs.

19. Bruininks, R.H., Bruininks, R. Bruininks-Oseretsky Test of Motor Proficiency, 2nd ed. BOT-2. Upper Saddle River, NJ: Pearson Assessment, 2005.

20. Burpee, J.D. Sensory integration and visual functions. In: Gentile M., ed. Functional visual behavior: A therapist’s guide to evaluation and treatment options. Bethesda, MD: American Occupational Therapy Association, 1997.

21. Burtner, P.A., Dukeminier, A., Ben, L., Qualls, C., Scott, K. Visual perceptual skills and related school functions in children with hemiplegic cerebral palsy. New Zealand Journal of Occupational Therapy. 2006;53(1):24–29.

22. Burtner, P.A., Wilhite, C., Bordegaray, J., Moedl, D., Roe, R.J., Savage, A.R. Critical review of visual perceptual tests frequently administered by pediatric therapists. Physical and Occupational Therapy in Pediatrics. 1997;17:39–61.

23. Caine, R.N., Caine, G., McClintic, C., Klimek, K. 12 Brain mind learning principles in action. Thousand Oaks, CA: Corwin Press, 2005.

24. Carbo, M. Reading Style Inventory (Revised). Roslyn, NY: National Reading Styles Institute, 1992.

25. Carbo, M. Reading styles times twenty. Educational Leadership. 1997;54:38–42.

26. Carbo, M. Becoming a great teacher of reading: Achieving high rapid reading gains with powerful, differentiated strategies. Thousand Oaks, CA: Corwin Press and National Association of Elementary School Principals, 2007.

27. Carbo, M. Best practices for achieving high, rapid reading gains. The Education Digest. 2008;73(7):57–61.

28. Cardona, M., Martinez, A.L., Hinojosa, J. Effectiveness of using a computer to improve attention to visual analysis activities of five preschool children with disabilities. Occupational Therapy International. 2000;7:42–56.

29. Caron, A., Caron, R. Processing of relational information as an index of infant risk. In: Friedman S., Sigman M., eds. Preterm birth and psychological development. New York: Academic Press, 1981.

30. Christenson, M.A., Rascho, B. Environmental cognition and age-related sensory change. Occupational Therapy Practice. 1989;1:28–35.

31. Cicerone, K.D. Evidence-based cognitive rehabilitation: Recommendations for clinical practice. Archives of Physical Medicine and Rehabilitation. 2000;81:1596–1615.

32. Ciner, E.B., Macks, B., Schanel-Klitsch, E. A cooperative demonstration project for early intervention vision services. Occupational Therapy Practice. 1991;3:42–56.

33. Clifton, R.K., Muir, D.W., Ashmead, D.H., Clarkson, M.G. Is visually guided reaching in early infancy a myth? Child Development. 1993;64:1099–1110.

34. Cohen, K.M. The development of strategies of visual search. In: Fisher D.F., Monty R.A., Senders J.W., eds. Eye movements: Cognition and visual perception. Hillsdale, NJ: Erlbaum, 1981.

35. Colarusso, R.P., Hammill, D.D. Motor-Free Visual Perception Test, 3rd ed. Novata, CA: Academic Therapy Publications, 2003.

36. Cooper, B.A. A model for implementing color contrast in the environment of the elderly. American Journal of Occupational Therapy. 1985;39:253–258.

37. Cratty, B.J. Perceptual and motor development in infants and children. New York: Macmillan, 1970.

38. Daly, C.J., Kelley, G.T., Krauss, A. Relationship between visual-motor integration and handwriting skills of children in kindergarten: A modified replication study. American Journal of Occupational Therapy. 2003;57:459–462.

39. Daniels, L.E., Ryley, C. Visual-perceptual and visual-motor performance in children with psychiatric disorders. Canadian Journal of Occupational Therapy. 1991;58(30):137–141.

40. Dankert, H.L., Davies, P.L., Gavin, W.J. Occupational therapy effects on visual-motor skills in preschool children. American Journal of Occupational Therapy. 2003;57:542–549.

41. de Boisferon, A.H., Bara, F., Gentaz, E., Cole, P. Preparation of young children to read: Effects of visual-haptic exploration of letters and visual perception of writing motions. L’Annee Psychologique. 2007;107:537–564.

42. D’Entremont, B., Hains, S.M.J., Muir, D.W. A demonstration of gaze following in 3-to-6 month olds. Infant Behavior and Development. 1997;20:569–572.

43. DeQuiros, J.B., Schranger, O.L. Neuropsychological fundamentals in learning disabilities. Novato, CA: Academic Therapy Publications, 1979.

44. Dunn, R., Griggs, S.A., Olson, J., Gorman, B., Beasley, M. A meta-analytic validation of the Dunn and Dunn learning styles model. Journal of Educational Research. 1995;88:353–363.

45. Durlach, N., Allen, G., Dorken, R., Garnett, R., Loomis, J., Templeman, J., et al. Virtual environments and the enhancement of spatial behavior. Presence: Teleoperators and Virtual Environments. 2000;9:593–616.

46. Dutton, G. Visual problems in children with damage to the brain. Visual Impairment Research–2002. 2002;4:113–121.

47. Dutton, G., Ballantyne, J., Boyd, G., Bradnam, M., Day, R., McCulloch, D., et al. Cortical visual dysfunction in children: A clinical study. Eye. 1996;10:302–309.

48. Enns, J.T., Cameron, S. Selective attention in young children: The relation between visual search, filtering, and priming. Journal of Experimental Child Psychology. 1987;44:38–63.

49. Farran, E.K., Cole, V.L. Perceptual grouping and distance estimates in typical and atypical development: Comparing performance across perception, drawing, and construction tasks. Brain & Cognition. 2008;68:157–165.

50. Fasotti, L., Kovacs, F., Eling, P., Brouwer, W.H. Time pressure management as a compensatory strategy training after closed head injury. Neuropsychological Rehabilitation. 2000;10:47–65.

51. Feder, K.P., Maynemer, A. Handwriting development, competency, and intervention. Developmental Medicine & Child Neurology. 2007;49:312–317.

52. Fegans, L.V., Merriwether, A. Visual discrimination of letter-like forms and its relationship to achievement over time in children with learning disabilities. Journal of Learning Disabilities. 1990;23:417–425.

53. Fox, T., Lincoln, N. Verbal mediation as a treatment strategy for children with non-verbal learning difficulties. International Journal of Therapy and Rehabilitation. 2008;15(7):315–320.

54. Gardner, M.F. Test of Pictures-Forms-Letters-Numbers-Spatial Orientation & Sequencing Skills. Burlington, CA: Psychological and Educational Publications, 1992.

55. Deleted in proofs.

56. Garzia, R. The relationship between visual efficiency problems and learning. In: Scheiman M.M., Rouse M.W., eds. Optometric management of learning-related vision problems. St. Louis: Mosby-Year Book, 1994.

57. Gentile, M. Functional visual behavior: A therapist’s guide to evaluation and treatment options. Bethesda, MD: American Occupational Therapy Association, 1997.

58. Gibson, E.J. Perceptual learning and the theory of word perception. Cognitive Psychology. 1991;2:351.

59. Gibson, E.J., Levin, H. The psychology of reading. Cambridge, MA: MIT Press, 1975.

60. Giles, D.C., Terrell, C.D. Visual sequential memory and spelling ability. Educational Psychology. 1997;17:245–253.

61. Gilfoyle, E., Grady, A., Moore, J. Children adapt, 2nd ed. Thorofare, NJ: Slack, 1990.

62. Glass, P. Development of visual function in preterm infants: Implications for early intervention. Infants and Young Children. 1993;6(1):11–20.

63. Goodale, M. Perception and action in the human visual system. In: Gazzaniga M.S., ed. The new cognitive neurosciences. 2nd ed. Cambridge, MA: MIT Press; 2000:365–377.

64. Goodale, M., Milner, L.S. Separate visual pathways for perception and action. Trends in Neuroscience. 1992;15:20–25.

65. Greene, L.J. Learning disabled and your child: A survival handbook. New York: Ballantine Books, 1987.

66. Griffin, J.R., Christensen, G.N., Wesson, M.D., Erickson, G.B. Optometric management of reading dysfunction. Boston: Butterworth-Heinemann, 1997.

67. Gulyas, B., Heywood, C.A., Popplewell, D.A., Roland, P.E., Cowey, A. A visual form discrimination from color or motion cues: Functional anatomy by positron emission tomography. Proceedings of the National Academy of Science USA. 1994;92:9965–9969.

68. Hammill, D.D., Pearson, N.A., Voress, J.K. Developmental Test of Visual Perception, 2nd ed. Austin, TX: Pro-Ed, 1993.

69. Hendry, S.H.C., Calkins, D.J. Neuronal chemistry and functional organization in the primate visual system. Trends in Neurosciences. 1998;21:244–349.

70. Hung, S.S., Fisher, A.G., Cermak, S.A. The performance of learning-disabled and normal young men on the test of visual-perceptual skills. American Journal of Occupational Therapy. 1987;41:790–797.

71. Hyvarinen, L. Assessment of visually impaired infants. Ophthalmology Clinics of North America. 1994;7:219–225.

72. Hyvarinen, L. Considerations in evaluation and treatment of the child with low vision. American Journal of Occupational Therapy. 1995;49:891–897.

73. Hyvarinen, L. Vision testing manual. La Salle, IL: Precision Vision, 1995.

74. Hyvarinen, L. Vision in children: Normal and abnormal. Medford, Ontario: Canadian Deaf, Blind and Rubella Association, 1988.

75. Ilg, F.L., Ames, L.B. School readiness. New York: Harper & Row, 1981.

76. Izard, C. Emotions and facial expressions: A perspective from differential emotions therapy. In: Russell J.A., Fernandez-Dols J.M., eds. The psychology of facial expression. New York: Cambridge University Press, 1997.

77. Jordan, B.A. Jordan Left-Right Reversal Test, 3rd ed. Los Angeles: Western Pscyhological Services, 1991.

78. Juel, C. Learning to read and write: A longitudinal study of 54 children from first through fourth grades. Journal of Educational Psychology. 1988;80:437–447.

79. Justice, L.M., Ezell, H.K. Descriptive analysis of written language awareness in children from low income households. Communication Disorders Quarterly. 2001;22:123–134.

80. Justice, L.M., Ezell, H.K. Use of storybook reading to increase print awareness in at-risk children. American Journal of Speech-Language Pathology. 2002;11:17–29.

81. Justice, L.M., Lankford, C. Preschool children’s visual attention to print during storybook reading: Pilot findings. Communication Disorders Quarterly. 2002;24(1):11–21.

82. Kandel, E.R., Schwartz, J.H., Jessell, T.M. Principles of neural science. New York: Elsevier Science, 1991.

83. Kavale, K. Meta-analysis of the relationship between visual perceptual skills and reading achievement. Journal of Learning Disabilities. 1982;15:42–51.

84. Kosslyn, S., Chabis, C.F., Marsolek, C.J., Koenig, O. Categorical versus coordinate spatial relations: Computational analyses and computer simulations. Journal of Experimental Psychology of Human Perceptual Performance. 1992;18:562–577.

85. Kulp, M., Earley, M., Mitchell, G., Timmerman, L., Frasco, C., Geiger, M., et al. Are visual perceptual skills related to mathematics ability in second through sixth grade children? Focus on Learning Problems in Mathematics, Optometry and Vision Science. 2004;80:431–436.

86. Kulp, M.T., Schmidt, P.P. Visual predictors of reading performance in kindergarten and first grade children. Optometry Vision Science. 1996;73:255–262.

87. Lee, S. A frame of reference for reversal errors in handwriting: A historical review of visual-perceptual theory. School System Special Interest Section Quarterly. 2006;13(1):1–4.

88. Leigh, R.J., Zee, D.S. Neurology of eye movements. Philadelphia: F.A. Davis, 1983.

89. Levine, M. Developmental variation and learning disorders. Cambridge, MA: Educators Publishing Service, 1987.

90. Levine, M., Hooper, S., Montgomery, J., et al. Learning disabilities: An interactive developmental paradigm. In: Lyon G.R., Gray D.B., Krasnegor N.A., Kavanagh J.F., eds. Better understanding learning disabilities: New views from research and their implications for education and public policy. Cambridge, MA: Educators Publishing Service, 1993.

91. Lukatela, G., Eaton, T., Lee, C., Turvey, M.T. Does visual word identification involve a sub-phonemic level? Cognition. 2001;78:B41–B52.

92. Luria, A. Higher cortical functions in man. New York: Basic Books, 1966.

93. Marr, D. Vision. San Francisco: Freeman, 1982.

94. Martin, N. Test of Visual Perceptual Skills, 3rd ed. Novato, CA: Academy Publishers, 2006.

95. McAvinue, L., O’Keeffe, F., McMackins, D., Robertson, I.H. Impaired sustained attention and error awareness in traumatic brain injury: Implications for sight. Neuropsychological Rehabilitation. 2005;15(5):569–587.

96. McCarty, M.E., Clifton, R.K., Ashmead, P.L., Lee, P., Goubet, N. How infants use vision for grasping objects. Child Development. 2001;72:973–987.

97. Menken, C., Cermak, S.A., Fisher, A.G. Evaluating the visual-perceptual skills of children with cerebral palsy. American Journal of Occupational Therapy. 1987;41(10):646–651.

98. Milner, A.D., Goodale, M.A. Visual pathways to perception and action. In: Hicks T.P., Molotchnikoff S., Ono T., eds. The visually responsive neuron: From basic neurophysiology to behavior. New York: Elsevier Science; 1993:317–337.

99. Muir, D.W., Nadel, J. Infant social perception. In: Slater A., ed. Perceptual development: Visual, auditory, and speech perception in infancy. East Sussex, UK: Psychology Press; 1998:247–286.

100. Necombe, F., Ratcliff, G., Disorders of spatial analysis. Boller, E., Grafman, J., eds. Handbook of neuropsychology, Vol. 2. New York: Elsevier Science, 1989.

101. Olsen, J.Z. Handwriting without tears: First grade printing teacher’s guide. Cabin John, MD: Handwriting Without Tears, 2008.

102. Optometric Extension Program Foundation. Santa Ana, CA: The Foundation, 2006.

103. Osterling, J., Dawson, G. Early recognition of children with autism: A study of first birthday videotapes. Journal of Autism and Developmental Disorders. 1994;24:247–257.

104. Parham, L.D. The relationship of sensory integrative development to achievement in elementary students: Four-year longitudinal patterns. Occupational Therapy Journal of Research. 1998;18:105–127.

105. Perov, A., Kozminsky, E. The effect of computer games practice on the development of visual perception skills in kindergarten children. Computers in the Schools. 1989;6(3/4):113–122.

106. Piaget, J. Development and learning. Ithaca, NY: Cornell University Press, 1964.

107. Pizur-Barnekow, K., Kraemer, G.W., Winters, J.M. Pilot study investigating infant vagal reactivity and visual behavior during object perception. American Journal of Occupational Therapy. 2008;62:198–205.

108. Quinn, P.C. Object and spatial categorization in young infants: “What” and “Where” in early visual perception. In: Slater A., ed. Perceptual development: Visual, auditory, and speech perception in infancy. Psychology Press, 1998.

109. Rafal, R.D., Posner, M.I. Cognitive theories of attention and the rehabilitation of attentional deficits. In: Meier M.J., Benton A.L., Diller L., eds. Neuropsychological rehabilitation. New York: Guilford Press, 1987.

110. Ratcliff, G. Perception and complex visual processes. In: Meier M.J., Benton A.L., Diller L., eds. Neuropsychological rehabilitation. New York: Guilford Press; 1987:182–201.

111. Raymond, J.E., Sorensen, R.E. Visual motion perception in children with dyslexia: Normal detection but abnormal integration. Visual Cognition. 1998;5:389–404.

112. Reid, D.T., Jutai, J. The Componential Assessment of Visual Perception manual. Toronto, Ontario: University of Toronto, Department of Occupational Therapy, 1994.

113. Reid, D.T., Jutai, J. A pilot study of perceived clinical usefulness of a new computer-based tool for assessment of visual perception in occupational therapy practice. Occupational Therapy International. 1997;4:81–98.

114. Reutzel, D.R., Smith, J.A. Accelerating struggling readers’ progress: A comparative analysis of expert opinion and current research recommendations. Reading and Writing Quarterly. 2004;20:63–89.

115. Ritty, J.M., Solan, H., Cool, S.J. Visual and sensory-motor functioning in the classroom: A preliminary report of ergonomic demands. Journal of the American Optometric Association. 1993;64(4):238–244.

116. Roder, B.J., Bushnell, E.W., Sasseville, A.M. Infant preferences for familiarity and novelty during the course of visual processing. Infancy. 2001;1(4):491–507.

117. Rogow, S.M. Visual perceptual problems of visually impaired children with developmental disabilities. Re:View. 1992;24(2):57–64.

118. Rogow, S.M., Rathwill, D. Seeing and knowing: An investigation of visual perception among children with severe visual impairments. Journal of Vision Rehabilitation. 1989;3(3):55–66.

119. Roley, S., Schneck, C. Sensory integration and the child with visual impairment and blindness. In: Smith Roley S., Blanche E., Schaff R., eds. Sensory integration and developmental disabilities. Tucson, AZ: Therapy Skill Builders, 2001.

120. Rose, S.A. Enhancing visual recognition memory in preterm infants. Developmental Psychology. 16(85), 1980.

121. Rosenhall, J., Johansson, E., Gilberg, C. Oculomotor findings in autistic children. Journal of Laryngeal Otology. 1988;102:435–439.

122. Rosner, J. Test of Visual Analysis Skills. Academic Therapy, 1999.

123. Sakata, H., Taira, M., Kusunoki, M., Murata, A., Tanaka, Y. The TINS lecture: The parietal association cortex in depth perception and visual control of hand action. Trends in Neurosciences. 1997;20(8):350–357.

124. Sands, S., Buchholz, E.S. The underutilization of computers to assist in the remediation of dyslexia. International Journal of Instructional Media. 1997;24(2):153–175.

125. Scheiman, M. Understanding and managing vision deficits: A guide for occupational therapists. Thorofare, NJ: Slack, 1997.

126. Scheiman, M., Gallaway, M., Coulter, R. Prevalence of vision and ocular disorders in a clinical pediatric population. Journal of the American Optometric Association. 1996;67:193–202.

127. Schneck, C.M. Intervention for visual perceptual problems. In: Case-Smith J., ed. Occupational therapy: Making a difference in the school system. Bethesda, MD: American Occupational Therapy Association, 1998.

128. Scholber, M., Mateer, C. Cognitive rehabilitation: An integrative neuropsychological approach. New York: Guilford Press, 2001.

129. Scott, L., McWhinnie, H., Taylor, L., Stevenson, M., Irons, P., Lewis, E., et al. Double-masked placebo-controlled trial of £9, precision spectral filters in children who use coloured overlays. Ophthalmic & Physiological Optics. 2002;14:365–370.

130. Seiderman, A.S., Marcus, S.E. 20/20 is not enough: The new world of vision. New York: Alfred A. Knopf, 1990.

131. Sergent, J. Judgments of relative position and distance on representations of spatial relations. Journal of Experimental Psychology: Human Perception and Performance. 1991;91:762–780.

132. Shaywitz, B.A. The Yale Center for the study of learning and attention: Longitudinal and neuro-biological studies. Learning Disabilities: A Multidisciplinary Journal. 1997;8:21–30.

133. Shaywitz, S.E. Dyslexia. New England Journal of Medicine. 1998;338:307–312.

134. Sigman, M., Parmelee, A. Visual preferences of four-month-old premature and full-term infants. Child Development. 1974;45:959–965.

135. Snow, C., Burns, M.S., Griffin, P. Preventing reading difficulties in young children. Washington, DC: National Academy Press, 1998.

136. Sortor, J., Kulp, M. Are the results of the Beery-Buktenica Developmental Test of Visual-Motor Integration and its subtest related to achievement test scores? Optometry and Vision Science. 2003;80:758–763.

137. Spelke, E.S., Cortelyou, A. Perceptual aspects of social knowing: Looking and listening in infancy. In: Lamb M.E., Sherrod L.R., eds. Infant social cognition: Empirical and theoretical considerations. Hillsdale, NJ: Erlbaum; 1981:61–83.

138. Stiers, P., De Cock, P., Vandenbussche, E. Separating visual perception and non-verbal intelligence in children with early brain injury. Brain and Development. 1999;21:397–406.

139. Stiles, S., Knox, R. Medical issues, treatments, and professionals. In: Holbrook M.C., ed. Children with visual impairments: A parent’s guide. Bethesda, MD: Woodbine House; 1996:21–48.

140. Suchoff, I.B. Visual-spatial development in the child, 2nd ed. New York: State University of New York, State College of Optometry, 1987.

141. Swinth, Y.L., Handley-Moore, D. Supplementary lesson 8: Handwriting, keyboarding, and literacy: What is the role of occupational therapy. In: Swinth Y.L., ed. Occupational therapy in school-based practice: Contemporary issues and trends. Bethesda, MD: American Occupational Therapy Association, 2004. [online course].

142. Teplin, S.W. Visual impairment in infants and young children. Infants and Young Children. 1995;8:18–51.

143. Thelan, D., Smith, L.B. A dynamic systems approach to the development of cognitions and action. Cambridge, MA: MIT Press, 1994.

144. Todd, V.R. Visual perceptual frame of reference: An information processing approach. In: Kramer P., Hinojosa J., eds. Frames of reference for pediatric occupational therapy. 2nd ed. Baltimore: Williams & Wilkins; 1999:205–256.

145. Toglia, J.P. Cognitive-perceptual retraining and rehabilitation. In: Crepeau E.B., Cohen E.S., Schell B.A.B., eds. Willard and Spackman’s occupational therapy. 10th ed. Philadelphia: Lippincott Williams & Wilkins; 2003:607–629.

146. Torgesen, J.K., Wagner, R.K., Rashotte, C.A. Longitudinal studies of phonological processing and reading. Journal of Learning Disabilities. 1994;27:276–286.

147. Tsai, C., Wilson, P.H., Wu, S.K. Role of visual-perceptual skills (non-motor) in children with developmental coordination disorder. Human Movement Science. 2008;27:649–664.

148. Tseng, M.H., Cermak, S.A. The influence of ergonomic factors and perceptual-motor abilities on handwriting performance. American Journal of Occupational Therapy. 1993;47:919–926.

149. Tseng, M.H., Murray, E.A. Differences in perceptual-motor measures in children with good and poor handwriting. Occupational Therapy Journal of Research. 1994;14:19–36.

150. Tsurumi, K., Todd, V. Tests of visual perception: What do they tell us? School System Special Interest Section Quarterly. 1998;5(4):1–4.

151. Turkewitz, G., Kenny, P.A. The role of developmental limitations of sensory input on sensory/perceptual organization. Developmental and Behavioral Pediatrics. 6(302), 1985.

152. Ulman, S. Visual routines. In: Pinker S., ed. Visual cognition. Cambridge: MIT Press; 1986:97–159.

153. Van der Geest, J.N., Kemner, C., Camfferman, G., Verbaten, M.N., Van Engeland, H. Looking at images with human figures: Comparison between autistic and normal children. Journal of Autism and Developmental Disorders. 2002;32(2):69–75.

154. Voyer, D., Voyer, S., Bryden, M.P. Magnitude of sex differences in spatial abilities: A meta-analysis and consideration of critical variables. Psychological Bulletin. 1995;117:250–270.

155. Wann, J., Kardirkamanathan, M. Variability in children’s handwriting: Computer diagnosis of writing difficulties. In: Wann J., Wing A., Sovik N., eds. Development of graphic skills: Research, perspectives, and educational implications. London: Academic Press; 1991:223–236.

156. Warren, M. Identification of visual scanning deficits in adults after CVA. American Journal of Occupational Therapy. 1990;44:391–399.

157. Warren, M. A hierarchical model for evaluation and treatment of visual perceptual dysfunction in adult acquired brain injury. I. American Journal of Occupational Therapy. 1993;47:42–54.

158. Warren, M. A hierarchical model for evaluation and treatment of visual perceptual dysfunction in adult acquired brain injury. II. American Journal of Occupational Therapy. 1993;47:55–66.

159. Weil, M.J., Cunningham-Amundson, S.J. Relationship between visuomotor and handwriting skills of children in kindergarten. American Journal of Occupational Therapy. 1994;48:982–988.

160. Westheimer, G., Levi, D.M. Depth attraction and repulsion of disparate foveal stimuli. Vision Research. 1987;27(8):1361–1368.

161. Williams, H. Perceptual and motor development. Englewood Cliffs, NJ: Prentice-Hall, 1983.

162. Willows, D.M., Terepocki, M. The relation of reversal errors to reading disabilities. In: Willows D.M., Kruk R.S., Corcois E., eds. Visual processes in reading and reading disabilities. Hillsdale, NJ: Erlbaum; 1993:265–286.

163. Ziviani, J. The development of graphmotor skills. In: Henderson A., Pehoski C., eds. Hand function in the child: Foundations for remediation. St. Louis: Mosby; 2006:184–193.

164. Ziviani, J., Hayes, A., Chant, D. Handwriting: A perceptual motor disturbance in children with myelomeningocele. Occupational Therapy Journal of Research. 1990;10:12–26.

165. Zoltan, B. Visual processing skills. Vision, perception, & cognition, 4th ed. Thorofare; NJ: Slack, 2007.