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Switch Scanning System

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The “normal” way to navigate around a Windows or Mac computer is with a keyboard and mouse. However, if you don't have the physical ability to move a mouse or type on a keyboard, you can use a feature included in Gus software called “switch/scanning".

Contents

What is a switch?

A switch is a simple device that has two states - on and off - just like a light switch.Switches come in a variety of different shapes and sizes and are operated in different ways. Usually this is through a push motion but you can also buy switches that you grasp, pull, suck or even blink into. The most common type of switch is the Jelly Bean Switch.

Who uses switches?

People who find it difficult to access the keyboard and the mouse can use a single switch or a combination of switches instead. Switches can help people with a variety of different physical disabilities, from mild conditions like RSI to complete paralysis.

They are also suitable for people with severe learning difficulties as they are a simple, understandable method of accessing a computer.

Assessing for switch access

The correct selection and positioning of a switch is extremely important and support should always be sought from an experienced assessor, occupational therapist or other specialist.


What are switches used for?

Although the switch itself is very simple we are fortunate to have very clever software that can do all sorts of amazing things with this humble access device.

The function of a switch could be broadly defined into two groups:

  • Primary Access Switching

This involves the use of a switch to operate a computer, communication aid, environmental control or a wheelchair. In Primary Access Switching, the user relies entirely on a switch or a number of switches to control this device.

  • Supplementary Access Switching

In these cases a switch plays a supplemental role in the access solution. The most common example is when a switch is used to replace the left mouse button because although the user can move the mouse, or mouse alternative such as a headpointer, they find it very difficult to operate the click button. See an animated demonstration (requires Flash).

How does switch scanning system work?

Switch/Scanning is comprised of two parts. The "switch" is a small device (see button) that detects very light pressure. When you press on it you will often hear a ‘click’ sound. This “switch” often has a short cord (3 foot) that is then plugged into a “switch interface”. The “switch interface” is a small USB device that is connected to the computer.

A common "switch"    "Swifty Switch interface"
A common "switch" "Swifty Switch interface"

The “switch” (see button) can be placed under a finger, toe or other body part that can be moved voluntarily to activate the switch. Once the "switch" is connected to the “switch interface” and the "scanning" mode is turned on. The user can make selections by simply activating (pressing) their switch.

The term "scanning" describes the manner in which items on the computer screen are sequentially highlighted, one after the other, until the user activates the switch to make their selection. In other words, the computer offers the user a series of choices which can be selected by pressing the switch.

Switch Scanning Methods

Single switch scanning

Image:Single_switch_scanning.jpg

Users who access a computer using a single-switch use a type of scanning called Autoscan. It is a suitable solution for people who struggle to operate two or more switches. Although a single switch is physcially easier to use than two switches it requires far greater concentration to keep up with the autoscan.

Two switch scanning

Switch A starts the scan. Switch B selects row or column. Switch A scans row or column. Switch B selects location. Press switch A to start the scan. The lights in the top row or the first column light. Hold down switch A to move the scan to the next row or column. You can also press and release the switch each time you want to move the scan to a new row or column. When you reach the row or column you want, press switch B. Then press and hold switch B to scan across or down. You can also press and release the switch until you reach the location you want. When you have reached the location you want, press switch B again. With this technique, switch 1 always moves you somewhere and switch 2 always chooses your locations.

Row/ column scanning

This is a more efficient switch scanning method for single- or multiple-switch users than a standard cell-by-cell scan. It is the most common scanning sequence. It typically involves highlighting one row after the other until the user presses their "switch" when the desired row is highlighted. Then the scanning sequence moves across the row, highlighting each item within the selected row until the user makes their selection again.

Row/Column, sometimes known as Group, scanning allows a lot of cells to be grouped together to lessen the amount of time, or switch presses, required to reach a target key. By grouping the cells together the amount of switch-presses or scan delays required to reach the same letter is reduced to just 10. That's a big difference but you can make the process even more efficient by changing the layout of the keyboard to match the user's frequency of use.

However, Row-column scanning is a very slow method of communication. Options for increasing text entry rate include 1) dynamically changing the configuration of the row-column matrix or 2) using rate-enhancement techniques like word prediction, but evidence suggests that increased cognitive load imposed by these methods on the user can result in little or no improvement in test generation rate. [1]

Related Links

wikipedia

video:

Ipad app for cerebral palsy patients

two switch scanning

References

  1. Adaptive one-switch row-column scanning Simpson, R.C. Koester, H.H.