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
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
>
>
>