RESNA 28th Annual Conference - Atlanta, Georgia
Barry Romich, P.E., Katya Hill, Ph.D., CCC-SLP, Blaise Liffick, Ph.D.
Some people with disabilities use single switch interface(s) for controlling their assistive technology. Their overall performance of various functions (communication, computer access, etc.) is often a function of the switch(es), switch placement, and the ability to operate them. Traditional intervention approaches were based on subjective and qualitative evidence rather than quantitative performance measurement. Software has been developed to facilitate the collection of data on switch operation. The software prompts activation, release, and repetitive activation of the switch and presents averaged results. Results can be used for guiding both the choice and placement of a switch. The software supports evidence-based practice. It is available as a free download from a web site.
Keywords: switch, performance measurement, data collection, evidence-based practice
For many people with disabilities, assistive technology (AT) can be helpful in achieving their educational, vocational, and personal goals. Assistive technology can be used for augmentative and alternative communication (AAC), computer access, aids to daily living (ADL), and other functions. For some people, the human interface with AT can be direct selection, such as using a keyboard or otherwise pointing to targets and making selections directly using various means. Such methods generally result in the highest performance.
However, some people who need AT cannot use direct selection or cannot use it well. For some of these people the use of one or more single switches is required. The ability to use switches is then of obvious interest (1). Single switches can take many forms and can be activated in many ways. The most common form is the mechanical button with an internal micro-switch. Another form is the P-Switch, based on a piezoelectric element that can be mounted to detect slight movement, such as raising the eyebrow. The piezoelectric element is connected to a small interface box with a relay output. Biological sensors that detect intentional signals such as EMG (electromyographic), EEG (electroencephelographic), or EOG (electro-occular) sense an input signal that is detected and an output relay is activated.
Single switches can be used to control scanning, in which choices are made available in a time sequence and chosen upon switch activation (2). Choices can be made from an array by first scanning rows and then scanning elements within the chosen row. Single switches also can be used in codes, such as Morse Code, either in combination or by distinguishing short and long activations.
In the delivery of AT professional services, evidence-based practice (EBP) has become the normal expectation (3). EBP involves three components: 1) evaluation of external evidence, 2) measurement of personal performance, and 3) the knowledge and skills of the service provider. EBP results in the highest performance possible. This is important to people who use AT. For some areas of AT, such as AAC, performance can directly influence the quality of life experienced by the individual.
When a form of single switch is being considered for the human interface, significant issues surround the selection and positioning of the switch and the development of switch skills. In the evaluation of external evidence, one would seek information on the performance that has been reported in the research literature and experienced by others in considering the switch alternatives.
After determining the various switch options to be considered, each must be tried. It is common that the same switch can be used in many different ways. For example, a button switch could be mounted for activation by head movement or by pushing with the foot. Pushing with the foot could be implemented in many different ways. The switch could be mounted to the front, left, right, top, or bottom of the foot. The performance may be quite different among these choices.
In addition to the actual performance, other factors such as ease of use and fatigue must be considered. Initial performance may not be indicative of long term performance after skills are acquired. This is an area where the research and information on use by others may be helpful.
For all of these considerations, the measurement of performance using a switch can be valuable. Without performance measurement, it is unlikely that the best performance for an individual will be achieved.
One of the goals for this initiative was to eliminate barriers to use. One common barrier is cost. If development costs and distribution costs could be kept to a minimum, this barrier could be eliminated. The nature of what was needed seemed to match the needs and skills of a computer science class with a focus on disability issues. Millersville University of Pennsylvania had been awarded an NSF grant to establish such a program and thus became partners in this work. The students in the class were divided into six teams of two and given the task of implementing the defined function.
Single Switch Performance Test (SSPT) is a clinical tool to facilitate the measurement of performance using a single switch. SSPT is software to allow a PC to be used to practice switch use and collect switch use data. SSPT measures three parameters: 1) time to activate the switch, 2) time to release the switch, and 3) speed of repeated switch activation. The opening screen allows the selection of background information and also the specific test to be administered. Stimulus is provided by the computer and can be visual and/or auditory.
The switch is connected to the computer through a USB mouse. A standard mouse can be modified by adding a mini phone jack in parallel with the left mouse button. The USB mouse purchase and modification can be done locally using instructions available at the web site of the AAC Institute. A modified USB mouse can be purchased through the AAC Institute web site or from other sources.
The Practice Mode is intended to allow the switch user to get a feel for the activation of the switch prior to administering performance tests. Some switches have an audible click that can be heard. However, some individuals may have hearing impairment, some switches have no click, and/or the site (e.g., under the foot) and/or ambient noise may preclude any activation feedback. In Practice Mode audio and visual feedback indicates activation of the switch and is maintained until the switch is released.
SSPT provides for saving and/or printing the results of the test session. The report includes the name of the subject, the name of the test administrator, the version of SSPT used, and the date and time from the computer clock. This will allow test results to be compared across time.
Six teams of students produced six different approaches to meeting the specification. Each has advantages and disadvantages. At the time of submission of this paper, the Java-based approach has the attraction that it could be used on both Macintosh and PC platforms. Comparative analysis is ongoing.
SSPT is intentionally simple in order to keep the support to a minimum and to allow free distribution. SSPT is not comprehensive. For example, it does not allow consideration of the anticipation factor or measure or report errors. More comprehensive collection and analysis of performance data is possible. More comprehensive measurement of switch performance may be available in other products, such as COMPASS software (4).
The primary application for SSPT is as a clinical tool for measuring switch performance. Obvious values are comparing the performance using different switches and comparing the performance using different control sites and methods. This data results in an objective approach to switch selection and placement.
Another application for SSPT is the ongoing evaluation of switch performance. This data provides feedback and can offer guidance relative to the acquisition of switch skills. Analysis of this data can indicate which methods and techniques are producing the desired outcomes and also can indicate when achievable levels of performance have been reached.
The secondary application for SSPT is research and product performance testing. The common availability of this tool allows for the common collection of data. Little is presently known about how people with disabilities learn and use switches. Switch developers can use SSPT to test their devices and to help AT practitioners understand the performance that can be achieved.
SSPT is available as a free download from the web site of the AAC Institute: www.aacinstitute.org.
Barry Romich, P.E.
338 Meadville Street
Edinboro, PA 16412