IDRC - Celebrating 25 Years

1993 - 2018

Continuing Our Work During COVID-19

Read the letter regarding COVID-19 by IDRC Director, Jutta Treviranus.

Linda Petty, O.T.(C)
Assistant Manager, Adaptive Technology Resource Centre
University of Toronto
130 St. George St., Toronto
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Linda Buskin, SL-P
Communication and Assitive Technology Dept.
Bloorview Childrens Hospital
25 Buchan Ct., Willowdale ON
Voice: (416) 494-2222
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

A cross-over of knowledge is needed between traditional vision specialists and the parents, therapists and teachers of children with physical disabilities. Studies show some 75-90% of children with severe impairments have a visual impairment and that 30-60% of individuals with a diagnosis of cerebral palsy(C.P.) have some form of visual impairment such as visual acuity loss, eye muscle imbalances, visual field deficits, visual perceptual skill delays and processing problems (Beukelman & Mirenda 1992; Erhardt, 1990; Mirenda & Mathy-Laikko, 1989).

Computers and alternative and augmentative communication(AAC) aids are generally visually based and can be adapted for motor impairment, whereas software and hardware modifications for the blind require normal hand function for full keyboard operation. When visual deficits are added to physical disabilities, different considerations are required to assist in accessing and device use. The purpose of this paper is to provide clinicians and educators with an understanding of:

  • the impact of neurological impairments on ocular motor control
  • the implications of tactile dysfunction in the neurologically impaired client
  • the visual and physical demands of accessing computers and communication aids
  • the components of functional vision and the effects of their impairment on augmentative communication device/aid design
  • general strategies and adaptations for enhansing visualization of communication aids/devices, computer use and educational materials.


Muscle Tone Disturbances:Tone refers to the degree of muscle tension and its resultant resistance to stretching. Persistent extremes of muscle tone are termed hypotonicity for decreased or low tone and hypertonicity for increased tone. Muscle tone affects eye musculature, impacting on ocular-motor control.

Hypotonicity/Low Tone

Low tone can influence how well children direct their gaze, as the head is kept in a position to facilitate trunk support and postural control. Eye movement and field of vision may be limited by the hyperextended neck postion. In the child with C.P., a hypotonic trunk is frequently paired with increased tone in the upper and lower extremities. Seating and positioning strategies are used to compensate for low tone when sitting in a wheelchair. For less impaired children, ensure proper seating with the feet flat on the floor and forearms stabilized on a table surface when the child is to manipulate objects in midline. If asked to work with the arms unsupported, the child may slump to one side and the effort of maintaining posture in the chair may reduce attention to the task at hand. With the trunk and head supported in mid-line, the mild or severely involved child is able to direct their gaze more functionally, although they may limit head turning to look to the periphery so as not to lose head control (Levack, 1991).

Hypertonicity/Increased Tone

Certain muscles are maintained in an excited state of excessive tension and resistance to stretch. Although these "tight" muscles give the appearance of strength, in reality their hypertonic state limits efficient control and coordination of movement. Increased tone also affects the eye musculature, as follows.

Extensor Spasticity: A pattern of whole body extension is commonly seen in children under 7 years with spasticity. The extension is usually accompanied by neck hyperextension and the eyes held in elevation. In unsupported lying on the back, the child will not be able to direct their gaze straight up or down towards their feet. A wedge cushion behind the head/shoulders can break the pattern of hyperextension by giving a chin tuck postition. In this position, visual stimuli can be presented in mid to lower fields, with stimuli behind the child s back minimized to inhibit eye elevation. When the child is supported in standing the preferred range for visual motor activities is wide ranges out to the side at shoulder height. Arm movements to the side at shoulder level facilitate active trunk extension, normalizing postural tone and therefore providing the greatest freedom for the eyes. Work at an easel is used so the eyes are looking ahead or in a slight depression. In a seated position, support will optimally allow the child to dissociate eyes from head and head from trunk and upper limbs (Geniale, 1991).

Flexor Spasticity: With this pattern the child pulls forward with head and trunk and arm flexion when seated. The eyes tend to move into depression. This pattern limits the ability to look ahead and to reach out in any direction. By reducing the components of flexion in a position or task the child is given the best opportunities to use vision effectively. In standing visual stimuli or tasks are designed to get the child to look ahead. Surfaces at upper chest level or an easel are used for positioning, with materials away from the chest to prevent eye depression. In sitting, encourage moving the arms out to the side of the body in ranges up to shoulder height, such as to a tilted communication board placed on to the side of the wheelchair tray. Avoid arm movements above shoulder height to the front of the body as they increase flexor pull, e.g. the use of a computer touch screen at eye level. Reposition visually dependent tasks to shoulder height or below, using tilted surfaces to reduce the need to use head flexion to see items in close to the body. A head down position when lying on the back over a wedge provides good visualization and arm movement for activities at or above eye level (Geniale, 1991).

Common Reflexes and Associated Reactions

Asymmetrical Tonic Neck Reflex (ATNR): If this reflex is present, when the head is turned to one side, changes in muscle tone are seen in straightening of the limbs on the face side and bending of limbs on the skull side, in a fencer like posture. The eyes move toward the face side and elevate. This is used by children functionally in attempts to reach with the hand to one side. It can impair visual attention to the flexed side and lower visual fields on the face side. This reflex can be inhibited with head flexion (chin tucking) or maintaining the head and upper extremity tasks closer to midline.

Symmetrical Tonic Neck Reflex (STNR): When the head is flexed, bringing the chin to the chest, there may be a corresponding bending( flexion) of the arms and straightening (extension) of the legs. When the head is lifted upward, the arms will straighten and the legs extend. When a child is asked to look up at an object, they may use this reflex to raise their head by straightening their arms. It interferes with tasks like holding the head up to see a computer monitor while using the arms in a flexed position for keyboarding.

Associated Reactions: These are increases in spasticity in the affected parts of the body during the use of less affected body parts. These reactions are sometimes observed in children with minimal neurological impairment as well as severe spasticity, usually in distal body parts e.g. hands, feet and eyes. So fisting of the more effected hand may be seen when the other hand grasps a pen during writing. Associated reactions interfere with the use of vision as they cause an increase in ocular-motor problems, most commonly strabismus. Modifying the task or positioning the person so the task requires less effort and muscle tension can help alleviate the associated reaction. Use of the child s own visual skills in the task in patterns which inhibit increased muscle tone also inhibits the reaction. So if the child is influenced by flexor tone, elevating the writing activity on a slanted desktop so their gaze is elevated away from their body and supporting the more effected arm in an elevated, weightbearing postion to the side will normalize tone, decreasing associated reactions of strabismus and hand flexion (Geniale, 1991).


Intact reception of tactile input is required for the communication modalities of Braille, tactile symbols and touch/in-hand signing. These modalities are successfully used with a varietyof visually impaired populations, however, cannot be transferred to individuals with Cerebral Palsy and visual impairnents without the following considerations:
  • As the tactile system is so extensive and because it interacts with so many of the other sensory systems, damage to the nervous system as a whole often involves damage to the tactile system (Short-DeGraff, 1988).
  • Very little research has been reported on the tactile reception of children with the neuromotor dysfunction of C.P., however, atypical responses to tactile stimuli are noted. Hypersensitivity or hyposensitivity to tactile input or delayed or unusual responses to touch are observed in the C.P. population and documented more extensively in Sensory Integration research with less impaired individuals.(Fisher et al, 1991)
  • The motor control to position the hand and move it over a Braille text may be limited, particularly for long term needs of accessing numerous lines/pages of text. The sensory receptors are most concentrated in the fingertips, however, hand control to isolate and use this body part functionally for Braille is frequently limited by abnormal muscle tone. Other body parts with fewer receptors for touch may not be sensitive enough to substitute,e.g. a fisted hand presents only the back of the fingers with fewer neuro-receptors for touch than the finger tips. Mouthing is frequently seen in children with impaired development of visual skills and manual manipulation skills, as the mouth area is rich in sensory receptors. Touching objects to the face near thelips can become a habitual way of gathering tactile information about an object. Habitual mouthing would therefore indicate under developed tactile reception and/or manipulation skills in the hands (Goold & Hummell, 1993).
  • The development of the tactile system is affected if tactile input is limited and motor response comprimised, as the perception of sensation interacts with motor response(DeGangi.1994).
An interdiciplinary team evaluation of the client's ability to use tactile input for touchcommunication, tactile symbols or Braille is recommended for clients with multiple impairments.


The visual demands of direct selection with a finger/thumb or a control extender such as a mouth stick to an interface such as a regular or miniature keyboard or membrane surface, (with or without keyguard) necessitates:
  • adequate acuity to match range of reach and screen position
  • intact visual fields for area in which interface can be positioned
  • oculomotor skills for focusing on interface, scanning for selection, gaze shift and fixation on screen if needed and
  • cortical visual skills for interpretation of symbols/letters and interpreting the screen activity.

Direct selection with larger body site (e.g. fist/foot) for an enlarged keyboard or programable interface also requires:

  • adequate acuity to match the larger range of reach, distance to screen and
  • requires intact visual fields for area in which the interface can be positioned. Indirect selection through multiple switches or joystick, activated with upper or lower extremities or head movement for directional scanning or an on-screen keyboard requires
  • adequate acuity for screen/device visualization
  • intact visual fields for the area in which a device can be positioned
  • oculomotor skills for focusing on interface, tracking scan, locating selection, gaze shift between switches/joystick and device if needed.

Single switch selection with any body part to select from a scanning array requires:

  • adequate acuity for screen/device viewing
  • intact visual field for area in which device can be positioned
  • oculomotor skills for focusing on interface, tracking scan and locating the selection.
Switch activativation with any body part for one, two or three switch Morse code requires:
  • acuity for screen viewing only
  • intact field for area in which device can be positioned
  • oculomotor skills for following line of text/ word prediction
  • and cognitive skills for encoding text.


Visual acuity loss includes myopia (nearsightedness), hyperopia (farsightedness) and astigmatism (visual distortion due to a misshapen cornea). The impact on type and size of symbols, positioning of the display will depend on the severity of the loss and the use of corrective lenses.

Visual field deficit or loss restricts the visual field and impairs the individual's ability to scan and gain an integrated view of items presented. This will affect the arrangement and placement of a display, point of fixation and head control. Visual tracking skills may need to be trained for reading and communication display use.

Oculomotor problems includes eye muscle disorders such as strabismus, nystagmus, accommodative insufficiency, resulting in difficulties fixating, shifting and focussing, scanning and tracking a moving target, fatigue, reduced acuity. This impacts on many aspects of AAC system including scanning and following scanning lights, outputting a reliable eyepoint, location of the device, configuration of the display and spacing of items on the display.

Visual stability is affected as some conditions fluctuate daily, or deteriorate over time, for example nystagmus, cortical visual impairment.

Visual perceptual difficulties include difficulties with figure-ground perception,visual discrimination, visual closure, visual memory and visual sequencing. These will affect the type of visual symbols and the arrangement of symbols on a display.

Colour reception will vary with type of impairment so determine which colors are helpful to the individual user.

Light sensitivity varies with etiology of problem--retinal problems may require more low light, acuity problems may require increased illumination. (The ABC's of vison in AAC, Augmentative Communication News, Sept. 1994).


Functional vision can be enhanced through the manipulation of visual design aspects of communication displays and educational materials and the choice of features of computers/devices:

The use of colour and contrast can facilitate visual discrimination, figure-ground perception and scanning through the use of background to increase contrast (black/white provides strongest contrast), increasing the width/boldness of lines, using colour to add more meaning to a picture. Colour may also serve as an identifies and organizer.

Space and arrangement of a display can be altered to limit visual clutter by simplifying picture, using solid colours with high contrast, reducing details and complexity of figure-ground, reducing the number of items on a display and allowing white space between and/or around items on a display and allowing white space between and/or around items and groups of items to accommodate visual perceptual and oculomotor difficulties. Spacing and arrangement of items may also enable use of eye pointing as a means of selection.

Size and distance alterations include magnification or increase in size of items and the positioning of items or display at an appropriate visual distance and within visual fields.

Texture enhancements heighten the contrast, provide a more concrete representation, and provide important compensatory tactile information.

Manipulating lighting and eliminating glare involve the careful selection of type of lighting to meet individual needs, and the identification of sources of glare e.g. student's dirty glasses. Altering the angle of view can also reduce glare. Positioning of lighting is best from behind so that lighting comes over the student's shoulder with the addition of task or spot lighting if necessary.

Adding voice output is a powerful means of compensating for visual impairment and includes the use of auditory feedback after selection has been made as a confirmation to the student, as well as auditory prompts or cues (with or without visual display) before a selection is made.

Consideration of scanning features of a device include evaluation of the scanning patterns (e.g. linear, circular), and the visual presentation of scanning (LEDs, highlighting/darkening of areas which vary considerably between devices.

Screen Scanning Software allows customisation of scanning array on a computer making it applicable to students requiring tangible symbols (these can be superimposed on the screen), customized graphics, personalized vocabulary, auditory feedback and prompts.

Specialized Word Processing Software includes features to enhance vision such as variable sizes, fonts, colours and contrast of text against background. Spacing can be increased, auditory feedback at letter, word, sentence levels can be added, as well as word prediction with or without auditory feedback. Some software also provides reading of menus and dialogues boxes, etc. Screen reading or screen magnification software can be used if adequate control of the keyboard available and if feedback is needed on the whole desktop and multiple applications.


As noted in the body of this paper, vision is a multifaced area with important implications for many augmentative communication users and their support teams. Strong links with vision specialists and thorough assessment and investigation of all areas of visual skills are recommended to ensure maximum use of augmentative communication aids. In-depth exploration of technology and strategies to enhance remaining sight or aid in sight substitution will give each augmentative communication/computer user the maximum capacity to learn and communicate.


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  2. Beukelman, D.R. & Mirenda, P.(1992)."Augmentative and Alternative Communication. Management of Severe Communication Disorders in Children & Adults", York, PA: The Maple Press Co.
  3. Bobath, B., (1985). "Abnormal Postural Reflex Activity Caused By Brain Lesions", Rockville, MD, Aspen Publication.
  4. DeGangi, G., (1994). "Documenting Sensorimotor Progress: A Pediatric Therapist's Guide", Tuscon,AZ, Neuro-Developmental Treatment Association and Therapy Skill Builders, Publishers.
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  6. Fisher, A., Murray, E. & Bundy, A., (1991). "Sensory Integration Theory and Practice",Philadelphia, PA, F.A. Davis Co.
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  8. Geniale, T.,(1991). "The Management of the Child with Cerebral Palsy and Low Vision-- A Neurodevelopmental Therapy Perspective", The Royal New South Wales Institute for Deaf and Blind Children, Monograph Series No.2, North Rocks, Austrailia, North Rocks Press.
  9. Langley, B., & Lombardino, L. (1991). "Neurodevelopmental Strategies For Managing Communication Disorders In Children With Severe Motor Dysfunction", Austin, TX: PRO-ED.
  10. Levack, N. (1991)"Low Vision: A Resource Guide With Adaptations For Students With Visual Impairments". Austin, TX:Texas School for the Blind and Visually Impaired.
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  12. Short-DeGraff, M., (1988). "Human Development for Occupational and Physical Therapists", Baltimore, MD, Williams & Wilkins.