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Hello Richard.
 
I am interested to hear you mention the problems with symmetry, I have long been wondering about the ethics of the possibility of someone ending up with an Acquired Postural Deformity through the use of a switch or joystick in a location that requires the repetitive use of a posture that is "unbalanced". Sometimes though there would seem to be no practical option if someone is to achieve their mobility goals. Similarly some people chose to adopt a poor posture in order to remain functional.
 
I read the article by Linda Burkhart and it was informative, although is seems to concentrate on the lower range of cognitive ability. The situation with two switch scanning for a scanning wheelchair direction controller is even more complex than that for use with a communication aid.
 
Firstly, A communication aid is inherently a two dimensional scenario. The client uses MOVE to advance the highlighted word through either column or row and the CHOSE switch to make selections. There are no timing considerations and the visual and cognitive load are all focussed on the one device, the one physical area. With powered mobility, the client has to concentrate first on the wheelchair scanner - and recognise that the spatial layout of the lights on the scanner are a representation of the possibilities of the direction of movement within a much larger three dimensional volume of space, which is not necessarily an easy thing to do. Then having selected their required direction, they have change their focus of attention to the environment around them, literally changing their optical focus, and at the same time, engage with their CHOSE switch in order to initiate movement. Having achieved some movement in the required direction, they must then shift their focus of attention back to the scanning display and re-chose the next direction. This can be an extremely laborious and time consuming process, where the cognitive load is constantly shifting from one task to another and back again.
 
Secondly, the operation of the CHOSE switch now becomes a timed task. They must decide when they can press the switch and when they must release it. The consequences of mis timing can be frustration in not achieving their goal, or at the other extreme, damage to equipment or injury to themselves or others. With a communication aid, it doesn't matter how long they hold the CHOSE switch, the desired outcome will be the same. The situation with the MOVE switch is slightly different depending if the location highlight continues to move when the switch is held down, or if it requires a press-and-release to move from location to location. If the highlighted location continues to move when the MOVE switch is held down, then this again becomes a timed function in deciding when to let go.
 
Thirdly, where the client is already using two switch scanning for their communication aid access, this is invariably a "momentary" switch selection activity, (Simon's comments not withstanding), particularly for the CHOSE switch. With a scanning wheelchair controller, the pattern of movement must be re-learnt, as the CHOSE switch must now be held down for an extended period of time in order to maintain travel in the required direction. This is particularly difficult when the head is used to operate the switches as sometimes a "muscular impulse" is used to initiate an inertial movement of the head which may have no force behind it when it gets to the switch. This nevertheless operates the switch in a momentary manner. When you have to hold down the switch, you need to use continuous muscular force to maintain contact with and operation of the switch. Mobility switches often have a higher spring rate in them in order to ensure that they are less likely to stick in the ON position with all the possible consequences that were mentioned before. This then returns us to the problem of Acquired Postural Deformity where a task or effort is predominantly biased to one side or direction.
 
FInally, consider the situation where we integrate a communication aid onto a powered wheelchair with a scanning direction indicator using two switch scanning for both functions. When the client is communicating they must use a short press to CHOSE. When the client is driving they must remember to use their long press to CHOSE. This is an added cognitive load over and above the use of either device. There is also the problem of nomenclature. When using  a scanning wheelchair direction controller, the client must use their MOVE switch to CHOSE which direction they want to move, and then use their CHOSE switch to MOVE in that direction. I an not sure what the solution to this one is.
 
You or I without any physical or cognitive impairment can do all of the these things without much effort, much like driving a car. The situation is somewhat different for an eight year old with CP, possibly poor head control and a learning difficulty.
 
Sorry to have gone on a bit, but as Simon has said, there is very little of this written down anywhere.
 
All I need to do now is learn how to store it on the WIKI
 
Best regards,
 
Geoff Harbach. I.Eng  MIED  IIPEM
Registered Clinical Technologist
LEPMIS
Special Controls for Special People
Integrated Systems for an Integrated Life Style
on the Web LEPMIS.co.uk e-mail [log in to unmask]
 
 
 
 
 
In a message dated 23/06/2006 16:39:22 GMT Daylight Time, [log in to unmask] writes:

My own experience with head switching underlines the importance of symetry

in movement where at all possible. A CP boy of ten years drove his

wheelchair at school very sucessfully with three head switches for a period

of four years. He was symptom free thoughout. However, he later accessed his

VOCA using a single head switch, as prescribed by the speech therapist.

Within a short time he complained of neck pain, which prompted a fundimental

review of his access.

More multidisciplinary communication required!

Richard Taylor BDS B Eng. MSc.

Assistive Technologist

Registered Clinical Technologist

Bournemouth

----- Original Message -----

From: "Richard Walter" <[log in to unmask]>

To: <[log in to unmask]>

Sent: Thursday, June 22, 2006 11:59 PM

Subject: Re: Step Scanning with Head Switches

> I must admit to being a little confused (- becoming increasingly

> frequent these days).

>

> What do you usually set for a scanning mode using two switches?

>

>

> Generally step scanning removes the need for timing but the student does

> obviously need to be able to physically operate the two switches.

> Something to watch is that two switch scanning (especially head scanning

> can (does) have repercussions on the whole physical posture and tone of

> the student.

> I sometimes try the choose switch as a hand switch and the move switch

> as a single head switch.

> Most of our pupils if thy are using head switches have poor hand/arm

control

> Since the choose switch is used less frequently it can be operated by a

> less controlled movement.

>

> Actually very few of our pupils are capable of controlling scanning

> access but It is also much easier to assist scan in a step scanning mode.

> for example see Linda Burkhart's article on

> www.lburkhart.com/hand2sw4s.htm.

>

> Richard Walter

> Meldreth Manor School

>

> Judge Simon wrote:

> > It only occured to me today that Step Scanning has a big advantage over

any

> > other scanning method for head switching... So I documented it here:

> >

http://assistech.org.uk/doku.php?id=experiencebase:generalat:switch_scanning

> > _with_head_switches (-;

> >

> > No doubt it is only me that has just twigged this.

> >

> > Cheers

> >

> > Simon

> >

> > Clinical Scientist

> > ACT

> > 0121 627 1627 ex 53245

> >

>

 

Colin Clayton BSc, CEng, MIEE, MIPEM
Great Ormond Street Hospital for Children
The Wolfson Centre
Mecklenburgh Square
London WC1N 2AP
Tel: 020 7837 7618
Fax: 020 7833 9469
visit www.wisedx.com
email: [log in to unmask]