Popslide idea

Moritz Moeller mnm at dneg.com
Tue Mar 25 13:46:55 CET 2008

Casper Boemann wrote:

> Looking at it physiologically you might be able to explain a lot, but in 
> practice it's mch simpler to move the hand sideways. The y direction of the 
> slider is locked so moving the hand in an arc is not a problem.
> And if i had to make a movement in the y direction (if the the slider was 
> vertical) then i would have to move the entire arm. I don't know about you, 
> but I rest my hand on top of the mouse so moving my fingers doesn't help in 
> moving the mouse.

We did an experiment with 20 graphic designers at uni (this is about 12 
years back). It (among many other things) involved several interface 
mock-ups that favoured either horizontal or vertical operated sliders 
and grids as well as a drawing applications. We tested both for mouse 
and tablet usage. We recorded joint angle over time on all joints up to 
the shoulder as well. We also looked at precision archived in each case 
and time taken to do so.

We found that when moving stuff vertically, even those of them that 
always had their whole hand on the mouse (vs just the tips of their 
fingers) would swap to take the palm off and control fine movement with 
their finger joints and wrist. As far as I recall there was just one guy 
that never took his palm of the mouse (and he had the worst performance 
in terms of both speed and precision).
For horizontal movements those that used the palm would always keep the 
whole hand on the mouse.

We also found that when using interfaces that favoured vertical 
movements, the applicants showed less symptoms of stress in their right 
shoulder(blade) muscles because this joint was hardly used (i.e. the 
probability of a "mouse arm/shoulder" decreased by favouring vertical 

Similarly, when holding a pen and doing vertical movements, the 
applicants were using the finger /and/ wrist joint(s). While when doing 
horizontal ones, they mostly kept the finger joints locked and used the 
wrist and shoulder to move the pen.
If they were allowed to, all of them would rotate the tablets so they 
could draw horizontal lines doing vertical movements again. The majority 
of them also preferred to rotate the tablets when they had to operate 
horizontal sliders precisely.

Although 20 people is not very representative, the data we got from this 
at the time was as much more unambiguous than we expected in suggesting 
that vertical movements should be favoured for mouse and pen interfaces 
-- at least for graphic designers.

Regarding the locking of the y axis: it doesn't matter because you do 
need to use the shoulder joint to travel equal distance in x. Of course, 
if the UI had arc-movement compensation, this could be avoided. Might be 
another thing that is worth looking into.

My point was mainly about precision. The more you get to the end of the 
hand, the better the joints are capable of doing fine motor functions. 
Most people's shoulder joint is not.
This then means that you need more space to perform a horizontal 
movement using wrist and shoulder with the same precision than it is to 
do a vertical one using fingers and wrist.
And this is of course ignoring the potential physiological consequences 
touched on above ("mouse arm", RSI).

In any case, for people that find they nevertheless prefer horizontal, 
there could always be an option.


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