Functional Vision Skills
for AAC Systems
Patricia A. Politano, M.A. CCC-SLP/L, ATP
Assistive Technology Unit, University of Illinois at Chicago
And
Janice E. Scharre, OD, MA, FCOVD, FAAO
Illinois Eye Institute, Illinois College of Optometry, Chicago, IL
ABSTRACT
This session will present functional vision information critical in the selection of a communication system. This will include vision issues which affect the arrangement of a display, how it is accessed and the optimal position of a display. Functional vision skills will be reviews in the context of their relationship to an individual's ability to utilize communication system. Through the use of case examples, strategies needed to maximize an individual's use of a communication system, given their functional vision skills, will be presented.
INTRODUCTION
Communication specialists are recognizing the need for functional vision information in the selection of augmentative and alternative communication systems (AAC). Vision plays a critical role in an individual’s ability to successfully access AAC systems. The optometrist can evaluate the patient’s visual efficiency and visual perceptual skills to provide information to the AAC evaluator which will aid in the determining the most appropriate AAC system for the individual. This presentation discusses different accessing methods and various symbol sets used with augmentative communication systems and the visual and visual perceptual skills needed to utilize these systems. In addition, different compensatory strategies are presented for some vision abnormalities.
There are various aspects of functional vision that are necessary for an individual to optimally use their visual system in communication. These include visual acuity, refractive error, binocular vision, oculomotor ability, accommodation, contrast sensitivity, color vision, and visual perceptual skills. For example, what level of visual acuity is needed in order to see the display set? Is a child with limited eye movement ability able to use an eye- pointing system for communication? Commonly seen visual abnormalities such as strabismus and nystagmus may adversely affect an individual’s ability to successfully access and/or use a communication system.
Individuals may be experiencing diplopia (double vision), or a visual field defect that will limit their full utilization of their visual field. This may dictate the placement of a device. In addition, in the case of nystagmus, many patients experience an area within their visual field where the nystagmoid movement is decreased; this would help determine the placement of a device, as well. Eye movement deficits may cause a loss of localization of the targets, loss of place, and confusion.
VISION ISSUES WITH DIFFERENT ACCESSING METHODS
Different accessing methods requires different skills. The vision skills needed for five accessing methods were studied. See the chart below.
|
ACCESS METHOD |
VISION SKILLS |
|
Touch |
• Need to maintain visual fixation on the target while moving hand to the desired square |
|
Eye Pointing |
• Need to be able to move eyes in all directions and shift gaze between objects/pictures/words and communication partner • Fatiguing if moving eyes and head together |
|
Chin/Head Pointer |
• Need to maintain fixation on the target while moving pointer to the desired square • Chin pointing requires downward gaze • Head pointer uses upward gaze when display is flat |
|
Optical Light Pointer |
• Need to calibrate so eyes are in midline position when the light is on the target • Eyes move with head |
|
Scanning |
• Need to maintain visual fixation on target while moving to activate the switch • Eyes need to move separate from head if the switch is activated by head movement |
VISION ISSUES WITH DIFFERENT DISPLAYS
When designing or selecting communication displays, communication specialists routinely consider the visual acuity of the AAC user. A closer study of different communication displays and symbol sets revealed that it may be necessary to gather other functional vision information as well. For example, communication displays for scanning and optical light pointing often have red LEDs areas inside, under, around or beside the communication symbol. This additional color through out the display can make it difficult for individuals with figure—ground problems. Displays which utilize multiple colors to enhance the identification of individual symbols present problems for individuals who have difficulty with visual scanning and searching. Monochrome computer screens and LCD displays can present problems for individuals with visual scanning and searching problems as well.
It is also important to be aware that some symbol sets require specific vision skills. The identification or use of some icons require the individual to use color vision and other detailed symbols require the individual to have better visual acuity than that required to discriminate one whole symbol from another. For example, to discriminate between a smiling face and a sad face, the individual needs to clearly see the details within the face. To utilize some Bliss symbols, the user needs to be able to clearly see each detail of the symbol, and to utilize all the information in some multiple meaning icons, the user needs to see small details of the symbol as well.
COMPENSATORY STRATEGIES
Different compensatory strategies can maximize an individual’s ability to access a communication system. The following are examples of some vision issues common among individuals using AAC Systems and some intervention options to be considered:
|
PRESENTING VISION ISSUES |
INTERVENTION OPTIONS |
|
Poor eye-hand coordination |
• Cue to maintain fixation while • Utilize spaces, keyguards or raised |
|
Significantly reduced field of vision |
• Position display in best visual field • Consider positioning devices vertically to minimize width of display |
|
Nystagmus |
• Identify null point. Consider null point when determining optimal position for the display. |
|
Difficulty visually scan all the symbols on a display |
• Utilize color to block off groups • Use the same pattern of symbol arrangement on each display • Position reoccurring messages in the same location on each display used |
|
Difficulty with fine discrimination between similar symbols |
• When possible, enhance drawings with color. • Use high contrast displays |
DISCUSSION
It is important that vision information is obtained and incorporated into the considerations made in the selection and design of AAC systems. It is important for communication specialists to continue to increase their understanding of the impact of different vision problems and continue to consider the vision requirements of new and different AAC systems as they are developed and made commercially available for AAC users.